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  • Influence of B4C coating on graphitization for diamond/WC-Fe-Ni composite
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-20
    Youhong Sun; Jinhao Wu; Linkai He; Baochang Liu; Chi Zhang; Qingnan Meng; Xuliang Zhang

    Diamond/WC-Fe-Ni composite is a potential composition for impregnated diamond drill bits. It is necessary to avoid the graphitization of the diamond from Fe and Ni under the powder metallurgy process. Boron carbide (B4C) was coated on diamond, and diamond/WC-Fe-Ni composites were consolidated by hot pressing at different temperatures. The influences of sintering temperature and interfacial structure on bending strength and wear behavior were investigated. The bending strength for diamond/WC-Fe-Ni composite was dependent on matrix densification and interfacial graphitization. Un-coated diamond was eroded by Fe-Ni matrix and partially converted to graphite during the sintering process at all sintering temperatures. In opposite, B4C coating was beneficial to matrix densification at a lower sintering temperature, and delayed the appearance of graphitization to around 1300 °C. Therefore, the diamond/WC-Fe-Ni composites with B4C coating exhibited larger bending strength and better wear behavior at a relative low sintering temperature.

    更新日期:2020-01-21
  • Effect of micro-blasting on the tribological properties of TiN/MT-TiCN/Al2O3/TiCNO coatings deposited by CVD
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-16
    Tongwei Shen; Lihui Zhu; Zhenyu Liu

    The effect of micro-blasting on the tribological properties of TiN/MT-TiCN/Al2O3/TiCNO coatings was studied. The multilayer coatings were deposited on cemented carbides by chemical vapor deposition. The microstructure, mechanical and tribological properties were investigated using X-ray diffraction, scanning electron microscopy (SEM), nano-mechanical testing system, scratch tester and reciprocating tribometer. The results show that micro-blasting significantly reduces the surface roughness and converts the residual tensile stress of Ti(C,N,O) top-layer and Al2O3 layer into compressive stress. Affected by the residual compressive stress, the hardness and adhesion strength are increased. More importantly, the friction coefficient is decreased attributed to the decreased surface roughness and improved hardness. Also, the wear resistance of micro-blasted TiN/MT-TiCN/Al2O3/TiCNO is superior due to higher hardness of Ti(C,N,O) top-layer, Al2O3 layer and adhesion strength of coatings. Especially for the total sliding time of 2 h, the wear volume and wear rate of micro-blasted coatings are 69.4% of as-deposited coatings, because micro-blasting helps to increase the adhesion strength and micro-cracking resistance, which play important roles in the improvement of wear resistance. Micro-blasting has a positive effect on the friction and wear properties of TiN/MT-TiCN/Al2O3/TiCNO multilayer coatings since the adverse impact of top-layer thinning is offset.

    更新日期:2020-01-17
  • Effect of Ni content and maceration metal on the microstructure and properties of WC based diamond composites
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-16
    Kai Zhang; Deguo Wang; Zhenquan Wang; Yang Li; Qin Zhou; Baolin Liu; Zhiqiao Wang

    The effects of Ni content and maceration metal on the microstructures and mechanical properties of the WC based diamond composites were investigated in an attempt to seek optimal Ni addition concentration and alloy type. The results indicate that the Cu-10Ni-5Mn-29Zn alloy is more suitable to be used as the matrix maceration metal of WC matrix materials. The bending strength of matrix samples increased up to approximately 10% upon 5 wt% Ni addition. The WC based diamond composite with 5 wt% Ni exhibited an optimal overall performance. The strengthening mechanisms of bending strength and diamond retention capabilities were revealed. The good diamond-holding and WC-holding capabilities and the reinforcement of toughness and the plastic of this Cu-10Ni-5Mn-29Zn alloy are the primary reasons for the excellent performance of composites.

    更新日期:2020-01-17
  • Oxidation behavior of Zr-Y alloyed Mo-Si-B based alloys
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-13
    Tao Yang; Xiping Guo

    Three Mo-Si-B based alloys (Mo-12Si-10B, Mo-12Si-10B-1Zr and Mo-12Si-10B-1Zr-0.3Y (at.%)) were fabricated to study the effects of Zr and especially further addition of Y on the oxidation behaviors of alloys at 1250 °C. Mo-12Si-10B alloy shows good oxidation resistance due to the formation of a protective SiO2 layer. However, as the result of the phase transformation of ZrO2, triggering the breaking up of the protective SiO2 layer, the addition of 1 at.% Zr (Mo-12Si-10B-1Zr alloy) leads to the catastrophic oxidation behavior. Further addition of 0.3 at.% Y (Mo-12Si-10B-1Zr-0.3Y alloy) eliminates this detrimental effect of Zr alloying by promoting the formation of monomorphic ZrSiO4 instead of polymorphic ZrO2 during oxidation. Besides, at the later oxidation stage (≥20 h), a continuous and compact Y2Si2O7 layer forms on the scale surface, further improving the oxidation resistance.

    更新日期:2020-01-14
  • 更新日期:2020-01-14
  • On the flow and work hardening behavior of tungsten heavy alloy 92W-5.5Ni-2.5Fe
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-13
    Ashutosh Panchal; K. Venugopal Reddy; P. Abdul Azeem; T.K. Nandy; A.K. Singh

    Present work describes flow and work hardening behavior of Tungsten Heavy Alloy 92W-5.5Ni-2.5Fe (wt%) in heat treated and swaged conditions. The morphology of W-grains in heat treated and swaged materials is equiaxed and elongated in longitudinal direction with same volume fraction, respectively. The swaged material depicts different contiguity values along transverse and longitudinal directions. The strength and elongation values in heat treated condition are smaller and larger than those of the swaged material. The difference in σYS and σUTS values is very small in swaged material. The true stress-true plastic strain curve of the alloy on log-log scale exhibits two slopes in heat treated condition and follows Ludwigson constitutive equation. This can be attributed to the differences in micro hardness values of W-grains and matrix phase. In contrast, the true stress-true plastic strain curve of the swaged alloy on log-log scale displays only single slope and follows Swift equation due to the presence of pre-strain in the material. Both the materials exhibit three typical stages (I, II and III) of work hardening and linear part of stage III follows KME model. The fracture surface of heat treated material consists of W-cleavage, W-W decohesion and matrix rupture in considerable proportions. In contrast, the swaged material displays the presence of mainly W-cleavage. The fraction of W-matrix failure is significantly small and more or less same in both the materials.

    更新日期:2020-01-14
  • In-situ metal binder-phase formation to make WC-FeNi Cermets with spark plasma sintering from WC, Fe, Ni, and carbon powders
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-13
    Corson L. Cramer; Alexander D. Preston; Kaka Ma; Peeyush Nandwana

    High-density WC-FeNi ceramic-metal (cermet) composites were fabricated using liquid-phase spark plasma sintering/field-assisted sintering technology (SPS/FAST) with in-situ formation of metal binder phase. The precursor materials were micron-sized powders of WC, Fe, Ni, and C. A low melting point from a eutectic reaction of the powders enabled the in-situ formation of FeNi alloy and facilitates liquid-phase sintering of the WC. The carbon powder was added to stabilize the formation of the binder phase. Electron backscatter diffraction (EBSD) was performed to measure grain size and orientation. The composite exhibited a 99% theoretical density and a microstructure consisting of rounded and contiguous WC grains. The average grain size is 10.5 μm. The composite has a maximum hardness of 16.1 GPa. This research provides a fast and cost-effective approach to fabricate hard metals.

    更新日期:2020-01-14
  • Effect of milling conditions and binder phase content on liquid phase sintering of heat treatable WC-Ni-Co-Cr-Al-Ti cemented carbides
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-13
    Tomas Soria Biurrun; Belen Lopez Ezquerra; Lorena Lozada Cabezas; Jose M. Sánchez Moreno

    The binder phase of WC based cemented carbides has been alloyed by adding two different aluminium compounds, AlN and TiAl3, to mixtures comprised of WC, Ni, Co and Cr3C2 powders. A more efficient alloying effect is obtained by TiAl3 additions likely due to its higher dissolution rate during liquid phase sintering. Shrinkage and melting phenomena are strongly affected by the energy of the milling process and the amount of metallic additions. The use of higher milling rotation speed induces higher oxidation of the powder mixtures and the subsequent formation of a higher volume fraction of alumina particles after sintering. Densification and WC grain growth are hindered by increasing the Al addition. Thus, full densification of alloys with higher Al additions require the use of HIP after standard vacuum sintering cycles. As-HIPed WC-Ni-Co-Cr-Al-Ti samples present a binder phase with precipitation of gamma prime similar to that found in as-cast Ni superalloys. The size, volume fraction and morphology of these precipitates has been modified by applying a standard solution treatment (1150 °C-2 h) followed by fast air cooling and subsequent aging at 600 °C and different dwelling times. Age hardening effects have been confirmed in the composition consisting of WC-12 wt% Co-12 wt% Ni-1.7 wt% Cr3C2-5 wt% TiAl3 after 100 h at this temperature.

    更新日期:2020-01-14
  • Comparative study of the microstructures and mechanical properties of laser metal deposited and vacuum arc melted refractory NbMoTαa medium-entropy alloy
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-11
    Qingyu Li; Hang Zhang; Dichen Li; Zihao Chen; Fu Wang; Mengjie Wu

    NbMoTa refractory medium-entropy alloy (MEA) was fabricated by laser metal deposition (LMD) and vacuum arc melting (VAM) respectively. The crystal structures of NbMoTa MEA under two processes are all single-phase solid solution of BCC structure. Compared with the MEA formed by VAM, the NbMoTa MEA formed by LMD has smaller grain size and component microscopic segregation. Due to the difference in cooling rate, cellular and columnar substructures are demonstrated within the grain of LMDed MEA while the substructure within the grain of VAMed alloy is typical dendritic. However, the refinement of the grains in LMDed MEA does not lead to improvements in mechanical properties. In this study, the theoretical yield strength of NbMoTa MEA is calculated through solid solution strengthening (SSS) theory. The theoretical value is consistent with the experimental value measured under VAM, which is higher than the experimental value of LMDed MEA. The main reason for this result is that there are some metallurgical defects like porosities and intergranular cracks appeared in the LMDed MEA. The EDS test showed there is no elemental segregation seen at both sides of the crack. The reason for the intergranular cracks can be attributed to the high residual thermal stress caused by the rapid solidification characteristic of LMD process.

    更新日期:2020-01-13
  • Evaluation of the mechanical properties of WC-FeAl composite coating fabricated by laser cladding method
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    Alireza Mostajeran; Reza Shoja-Razavi; Morteza Hadi; Mohammad Erfanmanesh; Masoud Barekat; Mohammad Savaghebi Firouzabadi

    WC-Co coating, which is a subcategory of Tungsten Carbide-based coatings, is prominent among a variety of industries. However, because of its expense, poisoning, and low corrosion resistance of Cobalt in acidic environments, alternative compositions have been designed. One of these alternatives is the Iron Aluminide intermetallic compound which can replace Cobalt. This study investigates laser cladding of WC-FeAl powder on a 321 Stainless-Steel substrate. WC-FeAl powders were synthesized by mechanical alloying of initial Aluminum and Iron powders, milled for 20 h, followed by an hour of annealing at 800 degrees Celsius. Then, the annealed particles were mechanically alloyed with WC powders for 50 h. The result of the X-ray diffraction (XRD) analysis showed that no brittle and destructive phase was formed during synthesis. Subsequently, powders were coated on the stainless-steel substrate by laser cladding method. Effect of the main parameters of the laser cladding, including laser power, laser probe velocity, and powder spray rate, on the coating properties, such as porosity, geometry, thickness and, dilution were studied. Results indicate that with a higher power of the laser, the penetration depth and the width of the coating increased. Besides, with a higher velocity of the laser probe, dilution and penetration depth decreased. Furthermore, the Higher rate of powder spray led to a thicker coating. The optimum parameters of different samples were 250 W power, 4 mm/s probe velocity, and 400 mg/s powder spray rate. Evaluation of the mechanical properties indicated that the 1600 Vickers hardness, 5.7 MPa.m1/2 fracture toughness, and 355 GPa Young's modulus were obtained. Besides, The evaluation of the mechanical properties of the coating showed that the hardness, fracture toughness, and elasticity modulus are 1600 V, 5.7 MPa.m1/2, and 355 GPa respectively. Obtained results revealed that in comparison with the WC-FeAl composite coating with 500 ppm additional Boron and WC-Co coating both fabricated by thermal spray coating, for the WC-FeAl coating studied in this investigation, respectively the hardness is 1.16 and 1.21 times higher and the fracture toughness is 2.5 and 2.8 times higher. As well, Young's modulus of the coating was 1.56 times higher than the WC-Co coating made by the laser cladding method.

    更新日期:2020-01-11
  • Surface damage during transient thermal load of 50% thickness reduced W-2% (Vol.) Y2O3 sheet with different recrystallization volume fraction
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    Xiang Zan; Jie Yan; Haitao Sun; Kang Wang; Youyun Lian; Xiaoyue Tan; Laima Luo; Xiang Liu; Yucheng Wu

    Thermal shock damage of tungsten as a plasma facing material (PFM) depends on thermal shock power density level, duration and repeated time, and microstructure of the sample. The recrystallization process will degrade the mechanical property of material and thus change the its thermal shock resistance. The effects of recrystallization volume fraction on thermal shock response of W-Y2O3 under different power density levels (0.22–0.44 GW/m2) has been systematically studied. Electron beam pulse of duration of 1 ms with 100 recycles was used to simulate the transient thermal load of fusion device. The changes of morphology, distance, depth, width of crack and surface roughness on the rolling direction-normal direction (RD-ND) surfaces of W-Y2O3 samples with different recrystallization volume fraction were investigated. The results showed that recrystallization process have significant influence on the thermal shock resistance of W-Y2O3 samples. For the rolled sample, crack depth, width and surface roughness increased with the increased of power density level while crack distance decreased. The partially and fully recrystallized samples showed significant wider crack networks and severe surface modification.

    更新日期:2020-01-11
  • Annealing induced shrinkage-fill effect of tungsten‑potassium alloys with trace titanium doping
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    Longqing Chen; Wenbin Qiu; Hao Deng; Xiaoliang Yang; Yangyipeng Song; Xudong Cui; Jun Zhu; Jun Tang

    The shrinkages presented in sintering process of tungsten alloys are extremely detrimental to their practical applications in fusion reactors. Positively in this work, we effectively reduced the shrinkages via synergistically applying Ti-doping and annealing process on tungsten‑potassium (WK) alloys. This shrinkage-fill effect only works in the one with trace amount of titanium doping, such as 0.05 wt%Ti or 0.5 wt%Ti. Due to such effect, the compressive strength was improved by ~18%. Based on morphological and elementary analyses, we speculated that the Ti-rich particles along the grain boundaries of WK alloys were activated and migrated into shrinkages during annealing. Further Ti doping (e.g. 1wt.%Ti) led to nanoscale grain refinement in WK alloys, which almost doubled the compressive strength. In this case, an unconventional grain-refinement model was proposed. Furthermore, anomalous grain growth was observed in WK-3wt.%Ti, which was attributed to the formation of Ti-rich regions and the corresponding raise of energy in grain boundaries. The fabricating strategies in this work may benefit the design of refractory tungsten alloys with less shrinkages and ultra-fine grains.

    更新日期:2020-01-11
  • Gradient cemented carbide with β-phase free surface layer formed by nitrogen source AlN
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    Tianen Yang; Ji Xiong; Guoliang Niu; Lei Liu; Qidi Luo; Duquan Zuo; Haibao Wang; Zhenghua Deng

    Using AlN as nitrogen source, the gradient cemented carbide with β-phase free surface layer was fabricated in situ by one-step vacuum sintering. The β-phase free layer was explored by phase characterization, elemental-distribution analysis, microstructure and fracture observation. The results indicated that it was feasible to obtain β-phase free layer when utilizing AlN as the nitrogen source. The AlN decomposition fell appreciably to lower temperature in the presence of binder Co and Ni under vacuum sintering. The thickness of β-phase free layer could be tailored by controlling AlN contents, and the nitride former Al remained in the β-phase free layer. When applying nitrogen source AlN, the relative Ti content in the subsurface layer was lower than that with the conventional nitrogen source Ti(C,N) or TiN. By contrast, Co enrichment in the β-phase free layer is less significant than Ni as a result of higher solidification temperature. WC phases were much coarser averagely in the β-phase free layer than in the bulk, which was considered to be favorable for resisting against fracture. The β-phase free layer containing Al played a substantially improved role on the transverse rupture strength when AlN addition was 0.6 wt% and 1.2 wt%, while it is detrimental to the transverse rupture strength due to the formation of the intermetallic phase of Al and binder when AlN addition was 1.8 wt%.

    更新日期:2020-01-11
  • Abrasive wear behavior of WC-10Co-4Cr cladding deposited by TIG welding process
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    Jasbir Singh; Lalit Thakur; Surjit Angra

    The aim of the present study is to fabricate a highly wear resistant WC-10Co-4Cr cladding on AISI 304 using the TIG welding process. The effect of current and speed on the microstructure, hardness, and abrasive wear of cladding was investigated. Tribological behaviour of the claddings slided against SiC emery paper was examined using pin-on-disc tribometer. FESEM, XRD and EDS spectrums were used to analyse the microstructure of cladding. Different parametric combination of current and speed has been used to produce the variation in heat input during the cladding. Process parameters, such as current and speed influence the solidification time which results in different kind of microstructure. The results revealed that the TIG cladding deposited at low heat input produces a hard and wear resistance cladding. Increase in hardness and wear resistance was attributed to the partially melted WC grains reinforced in CoCr matrix. SEM images showed the formation of wear tracks on the surface of worn out cladding. The wear tracks was formed due to the plastic deformation and extrusion of CoCr matrix. However, the cladding developed at low heat input shows relatively smooth surface with lesser depth of wear tracks.

    更新日期:2020-01-11
  • Sintering behavior of molybdenum‑copper and tungsten‑copper alloys by using ultrafine molybdenum and tungsten powders as raw materials
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    He Zhang; Wei-Cheng Cao; Chun-Yang Bu; Kai He; Kuo-Chih Chou; Guo-Hua Zhang

    In this paper, high quality Mo-(10–40) wt% Cu and W-(10–40) wt% Cu alloys were prepared by powder metallurgy using the ultrafine molybdenum and tungsten powders as raw materials. The molybdenum powder with the size of 100–200 nm and tungsten powder with the size of 50–100 nm were prepared by a two-step reduction-process composed of an insufficient carbothermal reduction reaction and the following deep reduction reaction by hydrogen. From the experimental results, it was concluded that at the sintering temperature of 1200 °C to 1300 °C, relative densities of the Mo-(10–40) wt% Cu and W-(10–40) wt% Cu sintered blocks can reach >98%, and at the same time, excellent physical and mechanical properties were achieved. Meanwhile, the larger the content of copper in the alloy, the lower the temperature required for densification. At 1300 °C, the relative density, microhardness and thermal conductivity of the Mo-10 wt% Cu and W-10 wt% Cu sintered blocks are 98.83% and 99.36%, 167 HV and 283 HV, 138.38 W·m−1·k−1 and 154.15 W·m−1·k−1, respectively. Whereas, at 1200 °C, the relative density, microhardness and thermal conductivity of the Mo-40 wt% Cu and W-40 wt% Cu sintered block are 99.68% and 98.87%, 150 HV and 207 HV, 138.38 W·m−1·k−1 and 154.15 W·m−1·k−1, respectively. The present method was much more convenient relative to the traditional infiltration method.

    更新日期:2020-01-11
  • Perspectives of metal-diamond composites additive manufacturing using SLM-SPS and other techniques for increased wear-impact resistance
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-10
    Ramin Rahmani; Miha Brojan; Maksim Antonov; Konda Gokuldoss Prashanth

    In this paper, a new route is introduced to fabricate parts with increased wear and impact resistance for use in tunneling and mining applications. A combination of selective laser melting (SLM) and spark plasma sintering (SPS) to 3D print functionally graded lattices (FGL) that are later filled with metal-diamond composites was used. It was demonstrated that a cellular lattice plays an important role in the consolidation of diamond particles. Impact-abrasive laboratory experiments with tribological device, developed in-house, were carried out to characterize the fabricated samples. The results show that the balance of nickel, molybdenum, and chromium significantly affects the performance of the fabricated specimens. The addition of a higher content of MoCr, Ni and coated diamond particles guarantees higher impact-abrasive resistance of the composite. Our experimental results show that the FGL structure allows a more accurate distribution of diamond particles (variable metal/refractory material content) across the structure and our finite element simulations showed increased ductility and impact absorption ability due to a more uniform distribution of stresses throughout the volume.

    更新日期:2020-01-11
  • High temperature tribology of heavily boron doped diamond films against steel
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-09
    A.V. Gaydaychuk; S.A. Linnik; S.P. Zenkin

    Despite the fact that Fe, Co, and Ni catalyze the phase transition of diamond into graphite, the question of the applicability of diamond as a functional coating of a metal-cutting tool is still open. For this reason, our work contains investigation of wear and friction of heavily boron doped diamond films against steel at elevated temperature, as well as influence of boron concentration on diamond film oxidation resistance. The obtained data indicated that minimum CoF value is achieved in the temperature range within 570–670 °C and strongly depends on boron concentration in coating (CoF decreases with increasing of boron concentration). Wear rate has the same dependence as the CoF, whereas oxidation resistance decreases with increasing of boron concentration. Besides, the presented results are first obtained for boron doped diamond films synthesized under high B/C ratio conditions (of up to 333 ppm).

    更新日期:2020-01-09
  • Evaluating crystal-orientation-dependent properties on polycrystalline tungsten: Example oxidation
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-08
    Karsten Schlueter; Martin Balden; Tiago da Silva

    Various material properties, like oxidation, depend on the surface orientation of crystals. Most evaluations are focused on a few crystal orientations or using single crystals. A software tool written in python is introduced to correlate the thickness of the tungsten (W) oxide layer, i.e., the oxidation rate, and the individual single crystal grains with their surface orientation of polycrystalline W. The results are visualized in an inverse pole figure, which represent the oxidation rates for all crystal orientations. The use of polycrystalline W samples allow to analyze many different crystal orientations in a single experiment. Recrystallized, polished and polycrystalline W samples were pre-characterized using electron backscatter diffraction in a scanning electron microscope (SEM). Subsequently, the samples were oxidized in a thermobalance. A confocal laser scanning microscope was used for measuring the height of the oxide layer, which is scaled to thickness of the oxide layer by using SEM images from focused ion beam prepared cross-sections. The previous data of oxidation of W in the temperature range of 720 K to 870 K were reanalyzed with the new analysis tool. At grain boundaries, the oxidation is influenced by the neighboring grains. To evaluate the magnitude of this effect on the oxidation, samples with different textures were oxidized and evaluated. The results for the different textures agree within the estimated error bars, demonstrating the effectiveness of the automated analysis method. W grains with 〈100〉 surface orientation presented the highest oxidation rate.

    更新日期:2020-01-08
  • 更新日期:2020-01-07
  • Composition of the Mo-Mo3Si alloys obtained via various methods
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-07
    Ivan Gnesin; Boris Gnesin

    The phase and chemical composition of an MoSi system alloy with a silicon content of 25 at.% was investigated via scanning electron microscopy, X-ray microanalysis, and X-ray diffraction. The samples were obtained by both sintering and melting of the components. The synthesis of Mo3Si from elemental Mo and Si via a sintering process at ≤1480 °C was significantly less complete than the synthesis of MoSi2, Mo5Si3 silicides via same process. To increase the efficiency of the synthesis, the reaction sintering of Mo3Si should be carried out at significantly higher temperatures than in the cases of MoSi2 and Mo5Si3 silicides synthesis. This offers a sufficiently phase-pure Mo3Si via reaction sintering at temperatures below the solidus. X-ray microanalysis data on Mo3Si chemical composition indicated a Mo3Si exists in a small compositional range. The average silicon content in Mo3Si was <25 at.%. In addition, experimental data indicated that the solubility of silicon in molybdenum may be higher than previously thought. Furthermore, the composition of the melt-quenched samples suggests that the solidus line for a Si solution in Mo may be retrograde.

    更新日期:2020-01-07
  • Fabrication of niobium carbide coating on niobium by interstitial carburization
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-07
    Ziyuan Zhao; Pengfei Hui; Fuyuan Liu; Yunhua Xu; Lisheng Zhong; Mingxuan Zhao

    Ceramic coatings on niobium substrates are fabricated by hot-pressing the niobium with cast iron at 1100 °C. The interstitial carbon atoms diffuse into the niobium, and NbC and Nb2C precipitate in the surface, forming a ceramic coating. The total volume fraction of the ceramic phases in the coating reaches 92%, and the grain size is in the range of 170–1000 nm. Both the volume fraction and the grain size of the ceramic phases decrease with increasing depth with respect to the coating surface, displaying a gradient microstructure. In the coating, the crystallographic orientations of NbC and Nb2C are randomly distributed. In the substrate, some isolated NbC and Nb2C nuclei exhibit the Kurdjumov–Sachs orientation relationship and the Porter orientation relationship with the matrix respectively, namely 11¯1101¯NbC//11¯0111¯Nb and 101¯00001Nb2C//11011¯5Nb. The coating remarkably improves the surface hardness of the niobium from 110 HV to 1600 HV, and it is strongly bonded with the substrate.

    更新日期:2020-01-07
  • Study of the welding procedure in nanostructured super-hard Fe- (Cr, Mo, W) - (C, B) hardfacing
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-02
    J. Gramajo; A. Gualco; H. Svoboda

    The optimization of the tribological properties of the surfaces by means of hardfacing techniques has made great progress in the metallurgical field in recent times. Alloys of the Fe-Cr-C and Fe-C-B type present excellent wear performance under severe conditions, where the incorporation of Nb, Mo and W improves the performance of severe abrasive wear. In this context, new semi-automatic welding consumables have been designed that deposit iron base material of high alloy, with complex carboborides of W, Mo and Cr which present very high hardness and resistant to abrasive wear. The purpose of this work was to compare microstructural variations coupons welded with one or two layers, with or without shielding gas. The chemical composition was measured on each coupon, the microstructure was characterized by X-ray diffraction and scanning electron microscopy. Dilution percentage was determined and Vickers microhardness profiles (HV2) were made on the different phases (HV0.025). It was found that the dilution with and without shielding gas were 26% and 19%. The hardness was 960 and 1100 HV2. An increase in hardness was observed in the recrystallized areas, as well as a higher percentage of carboborides in the last bead.

    更新日期:2020-01-02
  • Chemical mechanism of chemical mechanical polishing of tungsten cobalt cemented carbide inserts
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2020-01-02
    Meijiao Mao; Wentao Chen; Jingli Liu; Zihua Hu; Changjiang Qin

    To explore the chemical mechanism of tungsten‑cobalt cemented carbide inserts in H2O2-based polishing fluid. Before and after the YG8 cemented carbide inserts were corroded, surface phase, element and structure were characterized by XRD and SEM/EDS. The chemical mechanism of tungsten‑cobalt carbide inserts during chemical mechanical polishing (CMP) was analyzed. XPS was utilized to analyze the corrosion products formed on the surface of YG8 cemented carbide inserts during chemical reaction to determine the chemical reaction equation. In the H2O2 environment, the electrode potential of the Co layer at the boundary between the binder phase with larger crystal domains and the hard phase is greater than the electrode potential of the intermediate layer γ(Co-W-C solid solution) phase and WC, which creates a potential difference between the three, and occurs galvanic corrosion. The hard phase WC is protected as the cathode of the entire battery and has a tendency to stabilize. The Co layer at the phase boundary is the most anode feature to be corroded and dissolved first. The γ phase of the intermediate layer serves as the secondary anode feature and serves also as the cathode of the Co layer. When the Co layer at the phase boundary is corroded to a certain extent, a galvanic couple is formed between the γ phase and the testing phase WC to cause corrosion. In addition, the binder phase with smaller crystal domains directly forms galvanic corrosion with WC. The chemical products created on the surface of the blades are Co3O4 and WO3. However, Co3O4 and WO3 oxide films are small in size and have little effect on material removal during polishing. When the binder phase corrosion on the blades surface reaches a critical point, the stress exerted by the polishing abrasive is basically concentrated on the WC particle surface. The strength of the WC particles that have lost the supporting effect of the binder phase becomes low and the structure becomes brittle. Under the mechanical scratching and compressive stress of the abrasive particles of the polishing solution, the smaller WC particles are directly pulled out. The surface layer of the larger WC particles is broken into WC grains, and then the surface layer is mechanically removed.

    更新日期:2020-01-02
  • Investigation on plastic deformation mechanism of ultra-coarse cemented carbide based on energy analysis
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-31
    Xuemei Liu; Chao Hou; Hao Lu; Huaxin Hu; Haibin Wang; Xiaoyan Song
    更新日期:2019-12-31
  • The effect of NiO catalyst on reduction, synthesis and binder content of TiC-Ni nanocomposite
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-17
    Danial Davoodi; Reza Miri; Amir Hossein Emami; Morteza Tayebi; Saman Salahshour

    In the present study, synthesis of TiC-Ni nanocomposite via magnesiothermic method was investigated. The effects of catalyst content on the mechanisms of TiO2 reduction and synthesis of TiC-Ni nanocomposite were evaluated. For this purpose, the powder mixture was milled at different NiO content. By adding 0.1–0.3 at.% NiO to the mixture and milling after combustion, it was found that the synthesis did not completely occur. In 0.4 at.% NiO to the mixture, the synthesis was completed and after leaching pure TiC was synthesis. Additionally, the effect of NiO on the binder content composite synthesis was examined. It was observed by increasing NiO content, combustion time decreased and Ni content in nanocomposite increased. TEM observations confirmed for 0.4 at.% NiO at initial powder pour TiC with spherical morphology and for >0.5 at.% NiO at initial powder TiC-Ni nanocomposite with semi- spherical morphology was synthesis.

    更新日期:2019-12-18
  • Micro-Raman and X-ray diffraction stress analysis of residual stresses in fatigue loaded leached polycrystalline diamond discs
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-17
    M. Vhareta; R.M. Erasmus; J.D. Comins

    Polycrystalline diamond (PCD) cylindrical tool-bits used in oil well drilling are susceptible to fracture due to the hostile environment of randomly occurring high impact loads. These tool-bits generally comprise of a PCD layer sintered onto a Co-cemented tungsten carbide substrate. The cobalt metallic phase primarily aids the formation of the diamond to diamond bonds, however during application the same cobalt expands much quicker than the diamond, breaking the very same bonds it helped to form in the first place, leading to premature failure of the tool bits. As the PCD is virtually a two-phase material comprised of cobalt and diamond, substantial volumes of the metallic phase can be removed through a leaching process without compromising the cohesiveness of the diamond matrix, with reported improved wear resistance and thermal stability. X-ray diffraction and Raman spectroscopy techniques were used to investigate residual stresses in leached polycrystalline diamond disc samples. A systematic investigation and evaluation of the average in-plane residual stress fields using the Raman technique showed a progressive shift of the residual stress state from a compressive stress state to an average tensile stress state as a function of increasing number of loading cycles. In contrast the X-ray diffraction method recorded compressive stresses for all the measurements even at the highest number of loading cycles. The apparent disagreement between the two sets of results were satisfactorily explained by considering the probing beam size and sampling depth for the two different but complementary techniques.

    更新日期:2019-12-18
  • Densified WCu composite fabricated via laser additive manufacturing
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-31
    Shuang Su, Yunzhuo Lu

    Tungsten-Copper (WCu) composites are promising materials for electrical and thermal applications. However, their fabrication remains limited using conventional techniques, such as powder metallurgy, which are not suitable for manufacturing densified complex WCu components. In this work, laser additive manufacturing (LAM) technology was introduced for fabricating W-25 wt%Cu composites. A densified WCu composite, free of apparent cracks and pores, is successfully synthesized using optimum process parameters of laser power 2000 W and laser scan speed 360 mm/min in an Ar atmosphere with less than 10 ppm O. The densification of WCu composites is owing to the sufficient wetting of solid W particles by the molten liquid Cu and the surface smoothing of the W particles. The good wetting of the solid W particles by the liquid Cu is due to the low oxygen content and the combined effect of increased capillary force and reduced friction force. The W grains are rounded, indicating some solution-reprecipitation of sharp particle edges originating from the increase in solubility from curvature effects.

    更新日期:2019-12-11
  • Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-24
    Xiangxing Deng, Núria Cinca, Dariusz Garbiec, José Manuel Torralba, Andrea García-Junceda

    Nanostructured Cr-based WC hardmetals are successfully sintered by spark plasma sintering. The wear behaviour of these Cr-based WC hardmetals with different C contents ranging from 5.57 wt% to 6.91 wt%, is evaluated performing sliding wear tests under two different wear conditions. This work analyses the influence of the C content on the wear performance through the study of the phase formation and WC grain size. The Cr-based hardmetal with 5.57 wt% C content exhibits a lower wear rate than Co-based WC hardmetals tested under similar dry ball-on-plate wear conditions, even considering that these Co-based WC hardmetals have higher WC content (90 wt%) than Cr-based WC hardmetals (83.2 wt%). The combination of a nanosized WC grain and the avoidance of brittle (Cr,Fe)7C3 or soft graphite phases leads to a superior wear performance. Thus, the use of Cr-based binders in the hardmetal industry, alternatively to Co-based binders, is promising in applications in which high wear resistance is needed.

    更新日期:2019-12-11
  • Investigation of wear resistance of drill bits with WC, Diamond-DLC, and TiAlSi coatings with respect to mechanical properties of rock
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-02
    Mostafa Piri, Hamid Hashemolhosseini, Reza Mikaeil, Mohammad Ataei, Alireza Baghbanan

    Drilling is an important engineering operation with extensive application in many fields of industry including mining engineering, oil and gas exploration and exploitation, civil engineering, groundwater management, etc. Drill bits must be able to endure enormous stresses that gradually wear them down during the drilling operation. In rock drilling, wear resistance is a key determinant of the drill bit lifetime and hence the drilling cost, thus basically affecting the choice of drilling method for any given rock type. With the advent of new wear-resistant materials, they can be used to improve the resistance of drill bits against wear and erosion. This study investigated the wear resistance of drill bits with tungsten carbide (WC) coating, DLC-Diamond coating, and titanium-silica‑aluminum (TiAlSi) coating when drilling in three types of hard rock, namely Khoshtinat Granite (A1), White Natanz Granite (A2) and Nehbandan Granite (A3). The drilling tests were performed on cuboid specimens using a drilling machine at rotation speeds of 850, 900 and 950 rpm and penetration rates of 12, 18 and 24 mm/min. The results showed that for any fixed drilling conditions, the wear rates of the TiAlSi drill bit in A1, A2, and A3 were respectively 48%, 52%, and 60% lower than those of the WC drill bit. In the same rocks, the Diamond-DLC drill bit also showed 42%, 44.25%, and 55% lower wear rates than the WC drill bit. in addition to the observed changes in wear rate of the drill bits, the surface roughness created by these drills represents the optimum performance of the TiAlSi drill bit. It was observed that, as the mechanical properties of the rock (uniaxial compressive strength, Mohs hardness, Schimazek's abrasivity index and Young's Modulus) increased, the tested drill bits showed wider differences in terms of wear resistance. As the TiAlSi drill bit had the lowest wear rate (27%) and after that, the Diamond-DLC drill bit showed a better wear (30%) performance than the WC drill bit (60%).

    更新日期:2019-12-11
  • Interdependence of slurry erosion wear performance and residual stress in WC-12wt%Co and WC-10wt%VC-12wt%Co HVOF coatings
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-25
    Andrew M. Venter, Vladimir Luzin, Deon Marais, Natasha Sacks, Enoch N. Ogunmuyiwa, Phil H. Shipway

    High-velocity-oxygen-fuel deposited WC-12wt%Co and WC-10wt%VC-12wt%Co hardmetal coatings are well anchored to the mild steel substrates, giving good mechanical integrity, as well as low porosity. The mechanical integrity has been investigated in terms of erosion performance and its influence on the residual stress state in the eroded regions. Wear slurry erosion tests reveal similar rates of erosion for both systems, that becomes more severe as the impact angle increases due to higher direct impact deformation normal to the surface. The 10wt%VC-12wt%Co coating renders slightly better erosion performance throughout. Stress evaluations using X-ray and neutron diffraction reveal substantial compressive residual stresses in the WC-phases for both coating compositions in their as-coated conditions. Within their erosion scars, the stresses become more compressive with erosion angle due to the increased impact component normal to the surface. It is concluded that the better wear performance of the WC-10wt%VC-12wt%Co coatings with impact angle, correlates with larger induced in-plane compressive stresses in the WC phase.

    更新日期:2019-12-11
  • Simulation, forming process and mechanical property of Cu-Sn-Ti/diamond composites fabricated by selective laser melting
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-04
    Jie Gan, Hui Gao, Shifeng Wen, Yan Zhou, Songcheng Tan, Longchen Duan

    Metal bond diamond abrasive tools with complex structure and high wear efficiency will be widely used in the geological drilling and mechanical processing industries, but are difficult to manufacture by traditional technology. In this paper, selective laser melting (SLM), as one of the additive manufacturing technologies, was used to fabricate Cu-Sn-Ti bonded diamond abrasive composites. Simulations, experiments and characterization were carried out to obtain the appropriate SLM process parameters. Results indicated that the optimal SLM parameters were laser power of 260 W, scanning speed of 300 mm/s and layer thickness of 0.09 mm. Furthermore, the wear resistant performance of SLM sample was compared with hot-pressed sintered sample in terms of mass loss rate, wear morphology and bonding condition. Results showed that diamond particles were seriously pulled-out from hot-pressed sintered sample while this hardly occurred from the wear surface of SLM sample, which was benefited from higher amounts of TiC around the diamond. Consequently, the bonding force to diamond was effectively improved for SLM sample. Therefore, SLM method cannot only fabricated sample with complex structures, but also with better performance. This study provides a novel approach for forming metal bonded diamond tools by SLM in the future.

    更新日期:2019-12-11
  • Study on process optimization of WC-Co50 cermet composite coating by laser cladding
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-17
    Pengfei Fan, Guan Zhang

    In order to optimize the process of tungsten carbide (WC)-reinforced Co50 cermet composite coating by laser cladding, Co-based coatings with 40 wt% WC were deposited on the surface of cone bit 15MnNi4Mo steel by 4 kW fiber laser. A single-factor experiment was designed to study the variation of the geometrical size, dilution rate and hardness of cladding layers with the change of various factors. Then, an orthogonal experiment was designed to study the optimal parameters for the laser cladding process by taking the hardness and dilution rate of the coatings as comprehensive indexes. Based on the results of the above experiments, the mathematical model of the relationship between the geometrical size of the cladding layers with the process parameters was established by regression analysis. In addition, the three-dimensional structure and microstructure of the coatings were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results revealed that with the increase of the laser power, the width of the cladding layer, the depth of the molten pool and the dilution rate gradually increased, while the coating height remained basically unchanged. Additionally, with the increase of the scanning speed, the coating height and the molten pool depth were relatively greatly reduced, while the coating width decreased little. Furthermore, with the increase of the powder feeding rate, the width of the cladding layer, the molten pool depth and the dilution rate gradually decreased, while the coating height gradually increased. The optimal process parameters are as follows: laser power of 2.4 kW, scanning speed of 7 mm/s, and powder feeding rate of 0.5 g/s. The mathematical model established by regression analysis fitted the width of the cladding layer best, and the minimum relative error was only 0.023%. The microstructure showed that metallurgical bonding was achieved between the coatings and substrates. Also, the coatings were compact and free of defects such as cracks and pores.

    更新日期:2019-12-11
  • Three-dimensional printing of hard materials
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-15
    E. Carreño-Morelli, P. Alveen, S. Moseley, M. Rodriguez-Arbaizar, K. Cardoso

    Tungsten cemented carbide parts have been produced by the “Solvent on Granule” 3D-Printing technique. It consists in growing layer-by-layer a green part by spreading a powder-polymer granule bed, followed by selective solvent jetting, and layer consolidation after solvent evaporation. The granules are prepared by wet blending, drying, milling and sieving to appropriate size range. The printed green parts are consolidated by thermal debinding and liquid phase sintering. Fully dense WC-Co test parts and a drill bit have been produced from presintered powder and elementary Co powder. The microstructures are equivalent to those of press and sintered parts. Good shape retention and tolerances are achieved.

    更新日期:2019-12-11
  • Design of alternative binders for hard materials
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-09
    M. de Nicolás, H. Besharatloo, P. Alvaredo, J.J. Roa, L. Llanes, E. Gordo

    In the last years, a special interest has emerged towards the total or partial substitution of traditional cemented carbides composing elements. In this study, a systematic methodology is presented and used to design iron-based binders for WC and Ti(C,N) ceramic phases. First, metal alloy phase diagrams were simulated by means of Thermo-Calc® software, combining several alloying elements (Ni, Al, Cr, Mo and C) to fulfil the following criteria: provide high corrosion resistance, least number of phases present at room temperature and solidus-liquidus temperatures below 1500 °C. Two final compositions were chosen: Fe15Ni10Cr and Fe15Cr10Al. Next step was to validate the critical temperatures by means of differential thermal analysis tests and, finally, high-temperature wetting experiments were conducted to measure the contact angle between molten metal and ceramic phases. Resultant metal-ceramic region was studied by means of field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and nanoindentation techniques. As a proof of concept, samples with 80 vol% of Ti(C,N) and WC ceramic phases were prepared for a basic characterization. Both ceramic reinforcements were compared, and the presented methodology could satisfactorily be validated as a design procedure of alternative binders for hard materials.

    更新日期:2019-12-11
  • A computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-25
    Martin A. Gren, Erik Fransson, Göran Wahnström

    Interfaces and surfaces often play a vital role for the properties of polycrystalline materials, such as cemented carbides, and the study of these planar defects is, therefore, of great importance. Cemented carbides (or hardmetals) is a unique class of materials where hard carbide (WC) grains, usually micrometer sized, are embedded in a more ductile metal binder phase (usually Co) in order to combine superb strength with high hardness, making them ideal as tool material in e.g. metal machining. In the manufacturing and industrial usage of cemented carbides temperatures reach high levels, especially in the former case where the material is sintered at temperatures where the binder phase is a liquid. This is a computational study of the temperature dependence of interface and surface energies in WC–Co cemented carbides upto and above the melting temperature of Co. We make use of an analytical bond order potential (ABOP) fitted to density functional theory (DFT) data in order to make the free energy calculations feasible. A variety of free energy methods are used: including quasi harmonic approximation, temperature and thermodynamic integration, and calculation of liquid surface tension and work of adhesion for phase boundaries. We present the temperature dependent interface and surface energies for some typical cases, data which should be useful as a supplement to other studies limited to 0 K.

    更新日期:2019-12-11
  • Effects of Mo2C, Ni binder and laser surface modification on WC inserts for turning Ti-6Al-4V
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-09
    R.M. Genga, P. Zeman, J. Brajer, N.L. Ofem, P. Rokebrand, L.A. Cornish, N. Nelwalani, A. Janse van Vuuren, C. Polese

    The effects of rapid pulse electric current sintering (PECS), Ni as a Co binder substitute, Mo2C additions and laser surface modification (LSM) on the microstructure, mechanical properties and machining performance during roughing and finishing turning of Ti-6Al-4 V were investigated. Additions of Mo2C reduced the carbide grain size from 0.65 ± 0.01 μm to 0.5 ± 0.01 μm in liquid phase sintered (LPS) WC-Co/Ni cermets, with the PECS manufactured WC-0.5Cr3C2–3.5Mo2C-10Co (wt%) having the highest hardness. The LSM technique produced a ~2.5 μm self-carbide coating, increasing the surface hardness of all the samples. LSM was done to improve abrasion, attrition and thermal wear resistance. Turning was done at cuttings speeds (vc) of 45–120 m/min, depths of cut (ap) of 0.25–2.0 mm and feeds of 0.15–0.2 mm/revolution, under lubricated conditions. The developed inserts were compared to TH10 (an industrial reference), and performance was assessed by cutting forces, tool wear and tool life. The liquid phase sintered WC-0.5Cr3C2-10Co (wt%) and WC-0.5Cr3C2–3.5Mo2C-10Co (wt%) inserts had longer tool lives than TH10 during roughing at a cutting speed (vc) of 45 m/min, depth of cut (ap) of 2 mm and feed of 0.2 mm/revolution, although TH10 had the best tool life during finishing (vc = 120 m/min, ap = 0.25 mm and feed =0.15 mm/revolution). Generally, LSM had a negligible effect on tool life, WC-Ni based inserts had the shortest tool lives and LPS inserts performed better than PECS inserts.

    更新日期:2019-12-11
  • High-temperature sliding wear, elastic modulus and transverse rupture strength of Ni bonded NbC and WC cermets
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-04
    R.M. Genga, P. Rokebrand, L.A. Cornish, N. Nelwalani, G. Brandt, N. Kelling, M. Woydt, A. Janse van Vuuren, C. Polese

    The effects of rapid pulse electric current sintering (PECS), substitution of WC by NbC and Co by Ni, and carbide additives (TiC and Mo2C) on the microstructure, elastic modulus, B3B transverse rupture strength (TRS) and high temperature sliding wear on WC-Co, WC-Ni, NbC-Co and NbC-Ni cermets were studied. Additions of x% Mo2C and y% TiC (where x and y were <10 wt%), coupled with PECS, significantly refined the NbC-Ni cermet's carbide grain size from ~5.0 μm to <0.8 μm, giving mechanical properties comparable to WC-Co and WC-Ni cermets: >14 GPa hardness and ~10 MPa.m1/2 fracture toughness (KIC) and ball-on-three-balls (B3B) TRS > 1600 MPa. The sintering techniques had negligible effect on the samples' elastic and shear modulus, and all WC-based samples had higher elastic modulus than all NbC-based samples (by ~120 GPa). High temperature sliding wear tests were carried out using a ball-on-disk tribometer, with a 10 N force, at a sliding speed of 1.34 m/s for 0.8 km (10 min) and 2.4 km (30 min), using 100Cr6 (AISI 52100) steel balls at 400 °C and 0% humidity. For the 2.4 km sliding distance, all the WC cermets had lower wear volumes than NbC cermets, with LPS WC-0.5Cr3C2-10Co having the lowest wear volume. Additions of TiC and Mo2C to NbC-12Ni improved the sliding wear resistance, with TiC having the greater effect, reducing the sample wear rate by over 30% from 15.1 × 10−6 mm3/N·m to 9.4 × 10−6 mm3/N·m after sliding distance of 2.4 km. Generally, the LPS samples had lower wear volumes than the corresponding SPS samples, due to higher K1c and TRS.

    更新日期:2019-12-11
  • Optimization of electrolyte concentration for surface modification of tantalum using plasma electrolytic nitridation
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-08
    S. Padervand, M. Amiri, M. Mousavi khoei

    Plasma Electrolytic Nitriding (PEN) is a cathodic atmospheric plasma process which has shown a promising deposition of metal coatings that exhibits a significant adhesion to the substrate as well as high deposition rates. The structure of tantalum alloy, microhardness and corrosion resistance behavior after cathodic plasma electrolytic nitriding (PEN) in electrolyte containing urea and distilled water were investigated. An Optical microscope (OM), X-ray diffractometer and scanning electron microscopy (SEM) were used to characterize the phase composition of the modified layer and its surface morphology. The corrosion resistance properties of nitrided tantalum alloy are investigated. It was shown that various electrolytes provided metallic tantalum (Ta), TaN0.43, TaN0.1, Ta4N, Ta4N5 and TaN phases and nitrogen solid solution in tantalum. The cathodic PEN with 78 wt% urea and 21.6 wt% distilled water had a microhardness of 1198.18 VHN, which was selected as the best sample in term of electrolyte composition.

    更新日期:2019-12-11
  • Thermophysical properties of refractory W-50.4%Re and Mo-39.5%Re thin alloy layers deposited on silicon and silica substrates
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-08
    Dominika Trefon-Radziejewska, Justyna Juszczyk, Austin Fleming, Jacek Podwórny, Mihai Chirtoc, Nicolas Horny, Adriana Wrona, Marcin Lis, Michał Mazur, Damian Wojcieszak, Danuta Kaczmarek, Jerzy Bodzenta

    The examined samples were W-Re and Mo-Re thin alloy layers with high content of Rhenium, applied in industry as protective coatings. The 550 nm of W-50.4%Re and 580 nm of Mo-39.5%Re alloys were deposited on crystalline silicon and amorphous silica substrates by magnetron sputtering method. For thermal characterization of investigated layers the scanning thermal microscopy (SThM) and high frequency photothermal radiometry (HF-PTR) measurements were carried out. The thermal methods were supported by the microstructural studies performed by the atomic force microscopy (AFM) and X-ray diffraction (XRD). The SThM method allowed determining the thermal conductivity (κ) of the alloy layers. From the HF-PTR the effective thermal conductivity (κeff) was determined directly. Estimation of the thermal boundary resistance (Rth) between particular alloy layer and its substrate enabled determination of the real κ of the layer with its thermal diffusivity (α) and effusivity (ε) from the HF-PTR fitting. The results showed, that W-Re and Mo-Re layers deposited on Si are characterized by higher κ, α, and ε values, and lower Rth in comparison to those deposited on SiO2. The κ values for W-Re and Mo-Re layers deposited on Si and SiO2 substrates were estimated in the range from 7 W·m−1 K−1 to 12 W·m−1 K−1, and 1.6 W·m−1 K−1 to 4 W·m−1 K−1, respectively. The correlation between the alloy layer structure, it's thermophysical properties and substrate structure was observed. The AFM and XRD measurements confirmed the short range order formation in Mo-Re layers deposited on Si.

    更新日期:2019-12-11
  • Recovery of rhenium from tungsten‑rhenium wire by alkali fusion in KOH-K2CO3 binary molten salt
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-08
    Longgang Ye, Zhen Ouyang, Yongming Chen, Shufen Liu

    Tungsten‑rhenium wire is used in thermocouple and lamp filament manufacturing due to its good thermal sensitivity and high temperature plasticity, and many waste wires are generated in processing and after use. This work focuses on the efficient recovery of high value rhenium from tungsten‑rhenium wire waste with a mass composition represented by W95Re5. The main steps for recovery include alkali fusion, recrystallization, hydrogen reducing and washing. First, WRe wire was decomposed by KOH-K2CO3 molten salt to produce potassium perrhenate, where the decomposition ratios of W and Re reached 99.36% and 99.80% using a mass ratio of salt to wire of 3:1, m(KOH) of 80% (m representing the mass fraction of KOH in binary salt), a temperature of 800 °C and a reaction time of 60 min. Then, the decomposed product was leached by water, and from the resulting lixivium high purity KReO4 crystals were obtained by segregation, which had a perfect rhombic dipyramid morphology and average size of 73.26 μm. Last, the material was reduced to Re powder at 350 °C with a H2 flow rate of 10 L/min. Re powder, with a purity of higher than 99.5% and fine grain size of 19.37 μm, was obtained after washing with acid and water. This method provided a potential economic process for the recovery of waste WRe wire.

    更新日期:2019-12-11
  • C3H6N6 doping effect of synthetic diamond under high pressure and high temperature
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-11
    Junzhuo Wang, Shangsheng Li, Meihua Hu, Taichao Su, Guangjin Gao, Mingming Guo, Yue You, Yuan Nie

    In this paper, large diamond crystals were successfully synthesized under 5.6 GPa at temperature 1513 and 1553 K with melamine (C3H6N6) additive. Fourier transform infrared spectroscopy (FTIR) indicated C3H6N6 is an ideal nitrogen source for large diamond crystal synthesized by temperature gradient method (TGM), but its hydrogen is not absorbed by diamond. With the increase of C3H6N6 content, the colour of diamond changed from yellow to green, and the highest nitrogen content of diamond is 2300 ppm. High synthesis temperature can effectively reduce the formation of defects and play a key role in the formation of C-centers during diamond growth. Surprisingly, diamond is likely to grow into twin crystal when the C3H6N6 content is 0.1 wt%. In the process of diamond growth, carbon atoms of C3H6N6 are likely to serve as carbon source to form plane dislocations, which eventually lead to the formation of twin diamond. Raman spectra show that there are few crystal defects in diamond synthesized with C3H6N6 as dopant.

    更新日期:2019-12-11
  • The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-10-09
    Qi Wang, Zongde Liu, Yongtian Wang, Xinyu Wang

    The effects of (0–60%) vol% (70 vol% ZrB2 + 30 vol% SiC) additions on microstructure and properties of NbMo substrate fabricated by hot-pressing were studied at room temperature. Types of formed phase were decided by the amount of ZrB2 and SiC additives. The effective eutectic phase was observed in 15 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo, which was attributed to the addition of SiC. 30 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo had the highest relative density of 98.69%. Compared with x ZrB2-NbMo composites, the addition of SiC could further improve the hardness of NbMoss in x (70% ZrB2 + 30% SiC)-NbMo when the value of x was same, and NbMoss in 60 vol% (70 vol% ZrB2 + 30 vol% SiC)-NbMo had the highest hardness of 6.82 GPa. Only the 15 vol% (70 vol% ZrB2 + 30 vol% SiC) addition could improve the compressive strength of NbMo matrix. The reasons for the low strength of 30, 45, 60 vol% (70% ZrB2 + 30% SiC)-NbMo were the lack of ductile phase and the large amount of hard phase production.

    更新日期:2019-12-11
  • The effect of hot isostatic pressing on thermal conductivity of additively manufactured pure tungsten
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-06
    Jinhan Chen, Kailun Li, Yafei Wang, Leilei Xing, Chenfan Yu, Hailong Liu, Jing Ma, Wei Liu, Zhijian Shen

    The crack-healing behaviors and microstructure evolution of pure tungsten produced by laser powder bed fusion (LPBF) were studied and compared before and after post hot isostatic pressing (post-HIP) treatment. An average thermal conductivity of 133 W·m−1·K−1 at room temperature (RT) was obtained after HIP, which was 16% higher than that of as-built sample (115 W·m−1·K−1). Although the HIP process had little effect on density, it resulted in a large grain size of >300 μm accompanied by a decrease in dislocation density and crack healing, which led to a substantial improvement of thermal conductivity of pure tungsten. The positive correlation between relative density and thermal conductivity of as-built tungsten was reported.

    更新日期:2019-12-11
  • Comparison of wear characteristics of diamond segments under different sawing modes in sawing hard stone
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-11
    Shuo Wang, Jinsheng Zhang, Peiyu Dong

    In this study, the wear characteristics of two kinds of diamond segments with different composition of matrix were compared and investigated under two sawing modes through an experiment. Diamond particles were studied through scanning electron microscopy and three dimensional imaging system. Then, the remaining height of diamond segments was measured by digital vernier caliper. The wear characteristics of diamond segments were analyzed from wear morphology, protrusion height of diamond particles and the remaining height of diamond segments. The motion of two sawing modes and their effects on trajectories were analyzed which presented that the rocking reciprocating sawing mode can reduce sawing length and sawing time compared with horizontal reciprocating sawing mode used daily in industry. The results of experiment demonstrated that the main wear mechanism attributed to diamond segments wear is the fracture and falling of diamond particles caused by heavy loads especially in rocking reciprocating sawing mode. The average protrusion height of diamond particles is related with loads and the bonding strength of matrix. However, diamond segments wear can be effectively reduced in rocking reciprocating sawing mode while cobalt-based segments were adopted because a higher bonding strength to diamond particles can be provided compared with iron-based segments. The matrix of segments can be abrased slower while sawing length and sawing time were reduced.

    更新日期:2019-12-11
  • Study of the milling parameters optimization in the direct carburization of WO3 by mechanical alloying
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-20
    Victor Ioan Stanciu, Véronique Vitry, Fabienne Delaunois
    更新日期:2019-12-11
  • An investigation into the effects of HIP after sintering of WC-ZrC-Co-Cr3C2 cemented carbides
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-28
    Tomas Soria, Belen Lopez, Lorena Lozada, Steven Moseley, Patricia Alveen, Marc Elsen, Andrea Müller-Grunz, Michael Magin, Ralph Useldinger, Jose M. Sánchez

    The sintering behaviour of cemented carbides based on WC-ZrC-Co-Cr3C2 powder mixtures have been analyzed by dilatometric and calorimetric methods for different cobalt contents and WC/ZrC ratios. As expected, powder oxide reduction in these compositions is mainly of carbothermic nature. However, depending on the milling conditions, some highly stable Zr-rich oxides are retained in the binder phase after sintering. Hot isostatic pressing (HIP) cycles have been successfully applied for closing residual porosity after vacuum sintering. For a fixed amount of binder phase and a WC/ZrC ratio, the hardness of these materials depends on the amount of residual porosity and WC grain growth control. The best combination of hardness and toughness is found for alloys with 8 wt%Co and WC/ZrC wt. ratios of 6.46. HIP treatments induce the formation of a compact and well adhered layer mainly comprised of Zr oxides and WC grains. The cobalt binder phase migrates from this layer towards the sample bulk likely due to the loss of wettability on these Zr rich oxides. Hot hardness is higher for the alloy with higher WC/ZrC ratio suggesting that this property depends on both the volume fraction of (ZrxW1-x)C and WC phases and their degree of contiguity.

    更新日期:2019-12-11
  • Influence of the processing route on the properties of Ti(C,N)-Fe15Ni cermets
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-08-06
    M. de Nicolás, H. Besharatloo, J.M. Wheeler, M. de Dios, P. Alvaredo, J.J. Roa, B. Ferrari, L. Llanes, E. Gordo

    This study aims to understand the influence of powder preparation and processing steps on the microstructure and properties of Ti(C,N)-Fe15Ni cermets with 70 and 80 vol% of ceramic phase. Two routes were used for powder preparation: (i) a colloidal approach, consisting of the preparation of stable aqueous suspensions of the powder particles and spray-drying to obtain easy-to-press granules, and (ii) conventional powder metallurgy route, consisting on wet ball milling of powders, with subsequent drying in rotary evaporator. The resultant powder mixtures were uniaxially pressed and sintered in high-vacuum at 1450 °C for 2 h. Sintered samples were characterized in terms of their density, porosity, microstructure (FESEM, image analysis), composition (EDX and XRD), small-scale hardness and sliding contact response by means of massive nanoindentation and nanoscratch testing. C content of the mixture powders was lower for conventional route, lost during milling. After sintering, all the materials, despite the processing route and composition, show C reduction, although that outflow is higher for the conventional powder metallurgy route, and more evident for the composition with higher binder content. As a result, COL samples exhibit a more homogeneous microstructural assemblage, higher small-scale hardness and mechanical integrity under sliding contact conditions. Compositions of materials must then be adjusted to adequate initial C addition with respect to the employed processing route, to account for the effects of the mixtures preparation stage.

    更新日期:2019-12-11
  • Process optimization and modeling of recycling Mo (VI) from spent Mo-Fe2O3/Al2O3 catalyst by roasting with sodium carbonate using response surface methodology (RSM)
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-25
    Ruyi He, Da Li, Kunpeng Yang, Zhongkai Yang, Tao Li, Baozeng Ren

    The oil-containing spent Mo-Fe2O3/Al2O3 catalyst can be deemed as an environmental threat and an attractive source of minerals that can reduce the consumption of natural resources. Herein, recovery of Mo from spent Mo-Fe2O3/Al2O3 catalyst was conducted by the Na2CO3 roast-leach process, response surface methodology (RSM) coupled with central composite design (CCD) was employed to optimize the roasting process and a polynomial equation was derived to predict the response. The three roasting independent variables the roasting temperature, the Na2CO3/sample weight ratio, and the roasting duration were investigated in the Na2CO3 roasting process while water-leaching parameters were identical. The predictions of model showed that the roasting temperature had a major effect on the response with respect to other parameters. According to analysis of variance (ANOVA), the proprosed model equation had shown satisfactory agreement with the experimental data with a correlation coefficient (R2) of 0.9811. The optimum conditions for Mo recovery were predicted to be as the roasting temperature of 771.2 °C, the Na2CO3/sample weight ratio of 2.09 and the roasting duration of 93.56 min. Under the optimum conditions, maximal value of Mo recovery rate was reached as 92.58%.

    更新日期:2019-12-11
  • Effect of strain path change on the through-thickness microstructure during tantalum rolling
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-30
    Yahui Liu, Shifeng Liu, Nan Lin, Jialin Zhu, Chao Deng, Qing Liu

    High purity tantalum was respectively processed by unidirectional rolling (UR) and clock rolling (CR), and the through-thickness microstructures were investigated by multiple characterization techniques including electron backscatter diffraction (EBSD), Vickers hardness (HV) and X-ray diffraction (XRD). Results show that the through-thickness stored energy distribution in CR specimens is more homogeneous than in UR specimens due to uniform texture distribution. {111} grains possess larger Schmid factors and the corresponding Schmid factor difference ratio than {100} grains, indicating the activation of uniserial slipping in {111} grains, which leads to inhomogeneous deformation and higher stored energy. Besides, X-ray line profile analysis (XLPA) suggests that the stored energy of {111} grains increases successively from the surface to center layer, regardless of strain paths, due to the influence of redundant friction on the surface layers. While the occurrence of multiple slipping in {100} grains leads to homogeneous deformation and lower stored energy.

    更新日期:2019-12-11
  • Crack healing and strength recovery of Al2O3/TiC/TiB2 ceramic tool materials
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-28
    Zhaoqiang Chen, Lianggang Ji, Niansheng Guo, Chonghai Xu, Shuai Zhang

    Because ceramic tool materials are sensitive to defects such as microcracks, this paper develops ceramic tool materials with crack healing function to solve this problem. In this paper, Al2O3/TiC/TiB2 ceramic tool materials were prepared by vacuum hot pressing sintering technology. Cracks of different lengths are prefabricated on the surface of the material through Vickers hardness tester. The crack healing of the material was studied by high temperature air heat treatment. According to the recovery of material strength after heat treatment and the change of microstructure, the crack healing effect of the material was judged. The effects of different heat treatment temperature, heat treatment time and crack length on the healing behavior of ceramic materials were mainly studied. Research shows that the surface crack of the material is completely filled and healed by oxidation products. The flexural strength of the specimen with pre-cracked surface is only 24.50% of that of the smooth specimen. After heat treatment at 700 °C for 60 min, the strength of the cracked specimen returns to 91.35% of that of the smooth specimen. The maximum effective crack length for crack healing of this ceramic material is 500 μm. Through micro-morphology and elemental analysis, it is found that the main mechanism of surface crack healing is the filling and healing of cracks by liquid phase oxidation products of titanium diboride, namely boron trioxide and titanium dioxide, thus restoring the flexural strength of the material.

    更新日期:2019-12-11
  • Effects of fine WC particle size on the microstructure and mechanical properties of WC-8Co cemented carbides with dual-scale and dual-morphology WC grains
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-28
    Qingjun Ding, Yong Zheng, Zheng Ke, GuoTao Zhang, Hao Wu, XiangYu Xu, Xuepeng Lu, Xinggen Zhu

    Dual-scale and dual-morphology WC grained WC-8Co cemented carbides comprising triangular or hexagonal fine WC grains and plate-like coarse WC grains were synthesized by vacuum sintering using Co, flaky graphite, WC, and coarse W as the starting materials. The effects of fine WC particle sizes on microstructure, relative densities, and mechanical properties of the dual-scale and dual-morphology WC grained cemented carbides were investigated. The results revealed that the growth of plate-like coarse WC grains was further promoted with the decrease in the particle size of the added fine WC; hence, their aspect ratio increased. In addition, added fine WC led to the separation of plate-like coarse WC grains so as to break their oriented arrangement and prevent their face contact; hence, plate-like coarse WC grains were completely covered by the Co binder phase. Moreover, the addition of smaller particle size of fine WC contributed to more uniform Co binder phase. When 0.4-μm WC powders was added, the aspect ratio of plate-like coarse WC grains was greater than that of plate-like WC grained cemented carbides without the addition of fine WC. The dual-scale and dual-morphology WC grained cemented carbides by adding 0.4-μm fine WC exhibited good comprehensive mechanical properties, with a transverse rupture strength of 3645 MPa, a Rockwell hardness of 91.5 HRA, and a fracture toughness of 12.3 MPa∙m1/2.

    更新日期:2019-12-11
  • Metal matrix composites for fabricating tooling
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-02
    Thembani Togwe, Azim Gökçe, Yanyu Chen, Randall M. German, Sundar Atre

    The objective of this work is to investigate the fabrication, microstructures and, properties of metal matrix composites (MMCs) net-shaped using a four-step hybrid manufacturing method. The manufacturing method consisted of soft tooling fabrication, slurry casting, debinding-sintering followed by metal infiltration. Firstly, silicone rubber molds were fabricated. Subsequently, WC-Co pellets and stainless steel powders were mixed with polymer-based binders and cast into these rubber molds. After solidification, the parts were removed from the rubber molds, and placed in a furnace for debinding and sintering. Finally, sintered parts were infiltrated with bronze and the ensuing microstructures and properties were evaluated. The dimensional changes and mechanical properties of these MMCs as a function of amount of infiltrant were also examined. The results showed that the wear resistance of the MMC parts was comparable to M2 and D2 steels. Demonstrations of the process for net-shaping MMCs were conducted by fabricating wear-resistant tooling. The implications for fabricating MMCs by directly 3D printing rubber molds soft tooling are presented.

    更新日期:2019-12-11
  • Deformation and fracture of WC grains and grain boundaries in a WC-Co hardmetal during microcantilever bending tests
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-26
    Tamás Csanádi, Marek Vojtko, Ján Dusza

    The deformation and fracture behaviour of constituents of a WC-Co hardmetal were investigated by microcantilever bending technique. The compositions of FIB fabricated microcantilevers were: I) single grains of WC, II) WC grains of different orientations and III) the mixture of WC grains and Co phase. The crystallographic orientation of WC grains and the fracture surface of beams were studied by EBSD and SEM analyses, respectively. It was revealed that the elastic deformation depends mainly on the composition of the beams and the orientation of the WC grains. The Young's modulus of WC grains showed an orientation dependence with decreasing values from the basal (E~800 GPa) towards the prismatic orientations (E~500 GPa), which is in agreement with the theoretical predictions. The deformation behaviour of WC grains exhibited plasticity before their fracture with an average fracture strength of σ = 12.3 ± 3.8 GPa. It was found that the effect of dislocations and nanometre-sized defects (e.g. pores) plays an important role in the bending test of WC grains. Most of the WC/WC boundaries showed brittle failure with an average fracture strength of σ = 4.1 ± 2.5 GPa. It was concluded that the majority of the boundaries in the WC-Co composite are high energy WC/WC boundaries and their fracture strength is generally much lower than that of the WC grains.

    更新日期:2019-12-11
  • Effect of tungsten content on microstructure and mechanical properties of PCBN synthesized in cBN-Ti-Al-W system
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-03
    Mo Peicheng, Chen Chao, Jia Guang, Chen Jiarong, Xie Delong, Xiao Leyin, Pan Xiaoyi, Lin Feng

    Polycrystalline cubic boron nitride (PCBN) compacts were prepared using the mixture of cubic BN and Ti-Al-W powders at 5.5 GPa and 1550 °C for 10 min. The influence of different Tungsten (W) content on composition, microstructure, porosity, mechanical property and cutting performance of the PCBN is investigated. The results show that, with the addition of tungsten, the cubic boron nitride (cBN) crystals are connected with each other by the new product phases TiB2, TiN, Al3Ti and W2B under the pressure of 5.5 GPa and the temperature of 1550 °C. The rod-shaped crystals in the PCBN are expanded from the surface portion of the cBN. As the W content increases, the amount of rod-shaped crystals and the length-diameter ratios decrease in the system. When the tungsten content is 6 wt%, PCBN presents the best comprehensive performance and cutting performance, the porosity, the hardness, the flexural strength and the flank wear are 0.55%, 30.71 GPa, 972.3 MPa and 292 μm, respectively.

    更新日期:2019-12-11
  • Effect of Ni addition on the densification of TiC: A comparative study of conventional and microwave sintering
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-28
    Nivedhita Vasudevan, Nuzhet Nihaar Nasir Ahamed, Pavithra B, Ashwath Aravindhan, Balasivanandha Prabu Shanmugavel

    This study deals with the effect of conventional sintering and microwave sintering on the densification kinetics of Titanium Carbide (TiC) in the presence of Ni (1, 1.5, 2 wt%). TiC compacts were obtained after uniaxial pressing of powders synthesised by ball milling of Titanium and Carbon and sintering was done in the presence of Nickel. The samples prepared were subjected to conventional as well as microwave sintering. The XRD and SEM analysis were used for a study of the reaction of Ti and C powders upon addition of Ni, which reduced the sintering temperature to 1200 °C. The densification of TiC powders was due to the Ti-Ni eutectic system, the liquid phase formed at this temperature assisting the sintering process. The SEM images revealed the flake like structure of TiC in which the carbon diffused into Ti upon the addition of Ni, thereby supporting enhanced mass transfer. The XRD pattern showed the presence of Titanium Oxide (TiO2) along with TiC which resulted in non-uniform distribution of hardness. Maximum hardness was achieved in the conventional sintered compacts which gradually increased with increase in Ni addition. The presence of the oxide phase and the formation of micro cracks resulted in non-uniform hardness for microwave sintered compacts. The maximum hardness of conventional sintered compact (375 HLD) was nearly 1.5 times more than the maximum hardness of the microwave sintered compact (250 HLD). The density of the microwave sintered compact was found to be higher by 8% than with the conventionally sintered compact.

    更新日期:2019-12-11
  • Influence of microstructure on hardness and thermal conductivity of hardmetals
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-10
    A. Vornberger, J. Pötschke, T. Gestrich, M. Herrmann, A. Michaelis

    Hardmetals or cemented carbides are used in a wide range of applications due to their excellent mechanical properties. WC-Co hardmetals with the same room temperature hardness can be obtained by different combinations of the WC grain size and cobalt content. However, the thermal conductivity of such hardmetal grades is not equal. Applications such as cutting may require a certain combination of hardness and thermal conductivity, which means that a targeted adjustment is desirable. In this study a wide range of hardmetal grades was studied in respect of microstructure, hardness and thermal conductivity in the temperature range between 20 °C and 1000 °C. Results show that thermal conductivity is considerably influenced by Co content, WC grain size and Cr3C2 content. Furthermore, hardmetal grades with the same hardness at room temperature retain hardness very differently at elevated temperatures. For the selection of hardmetal grades for high temperature applications these findings help to choose the right composition in regard to Co content and WC grain size.

    更新日期:2019-12-11
  • Preparation of cemented carbide diamond films by gaseous boronizing pretreatment combines with self-assembly seeding process
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-10
    Liang Li, Qiuping Wei, Li Ma, Yijie Luo, Kechao Zhou, Mingkun Yi, Biao Deng, Yubo Chen

    In order to enhance the adhesion of cemented carbide diamond film and improve the cutting performance of cemented carbide diamond coating tools. This paper was the first to combine gaseous boronizing pretreatment with self-assembly seeding process to prepare diamond films on cemented carbide substrate. It not only eliminated the negative influence of cobalt (Co), but also improved the nucleation density of diamond. The gaseous boronizing pretreatment completed the boronation of the cemented carbide in a short time and obtained the CoWB phase which effectively prevented the diffusion of Co. By application of a self-assembly seeding process with the help of [2-(Methacryloyloxy) ethyl] trimethylammonium chloride (TMAEMC) highly improved the colloidal stability of nanodiamond (ND) particles. When the concentration of TMAEMC was 5 × 10−6 mol/l, the nucleation density of diamond was the highest. Rockwell indentation shows that the combination of gaseous boronizing pretreatment and TMAEMC self-assembly seeding process significantly improved the film-substrate adhesion. The reciprocating friction test shows that the diamond films prepared by this method had low friction coefficient and excellent wear resistance. Therefore, gaseous boronizing pretreatment combines with self-assembly seeding process is an effective way to achieve strong adhesion and high cutting performance of industrial diamond coating tools.

    更新日期:2019-12-11
  • In situ fabrication of TiC-NiCr cermets by selective laser melting
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-10
    Atefeh Aramian, Zohreh Sadeghian, Konda Gokuldoss Prashanth, Filippo Berto
    更新日期:2019-12-11
  • Determination of wear parameters and mechanisms of diamond/copper tools in marble stones cutting
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-12-10
    Hedayat Mohammad Soltani, Morteza Tayebi

    In this paper, a type of soft metal binder of diamond tools (diamond segments) that was consisted of 78% Brass (Cu10Zn) +16% Bronze (Cu10Sn) + %6Co was investigated. The first, it was approved that the binder is a soft metal binder by a hardness test for diamond tools in natural stones cutting. Then, the effective factors on grinding efficiency such as specific energy (SE), Cutting force (FC), metal binder removal rate (MRR), grinding ratio (G-ratio), wear resistance and Mean free path (MFP) were evaluated by different formula and equations. On the other hand, the effect of different wear mechanisms on the metal binder and diamond grits of the tool was evaluated by the cutting of a type of very hard marble stone that calls Cappochino Beige Marble (CBM). The existence of wears of abrasive, surface fatigue, impact and erosive were confirmed by scanning electron microscopic observations. According to hardness 73 HRB (hardness of the binder) and the wears, there is a short tools life for the diamond tool due to low wear resistance of the metal binder but, the cutting rate was high. Novelty statement The rising price of decorative stones will increase the final price of the stones and will overshadow the global market of decorative stones. The presence of cobalt, iron, chromium and nickel powders increases the price of diamond tools because of their high price. On the other hand, due to the higher temperature and time of hot press to produce these tools by the mentioned powders, it will also increase the price. Therefore, in this paper, brass and bronze alloy powders, which are much cheaper than cobalt, iron, chromium and nickel powders, have been used as main metal binder powders to reduce raw material prices and manufacturing process costs. On the other side, due to the creation of a softer metal binder compared with the more expensive and harder binder of cobalt, iron, chromium and nickel powders, it can be affected to increase the cutting speed because of increasing wear of the binder. Therefore, mathematical calculations are essential for the efficiency of the tools' cutting.

    更新日期:2019-12-11
  • Strain glass transition of cobalt phase in a cemented carbide
    Int. J. Refract. Met. Hard Mater. (IF 2.794) Pub Date : 2019-11-21
    S. Adjam, D. Mari, T. LaGrange

    Cemented carbides are hard materials used for the fabrication of cutting tools. They consist of hard micron or sub-micron carbide grains held together in a matrix of a tough metallic binder such as cobalt. The understanding and control of cobalt characteristics are of crucial importance to improve the mechanical properties of WC-Co cemented carbide materials. Indeed, cobalt controls the toughness of the material and its properties seem to condition the durability of cemented carbides. At low temperature, pure cobalt is normally found in hcp structure, while above 426 °C (700 K) it changes to fcc crystalline structure. Remarkably, in cemented carbides, cobalt appears even at low temperature as fcc, otherwise as a mixture of fcc and hcp. It is unsure if these crystal structures are due to the presence of internal stresses or due to W and C soluted atoms. However, this paper demonstrates that cobalt in WC-10wt.%Co cemented carbide may show some characteristics of a glass transition at around 669 °C (942 K) in the 1 Hz frequency range, inducing a glassy state to cobalt, which is of great interest from a fundamental point of view, however challenging to control in materials technology.

    更新日期:2019-12-11
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