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  • Adaptation and self-healing effect of tribo-oxidizing in high-speed sliding friction on ceramic composite ZrB2-SiС
    Wear (IF 2.95) Pub Date : 2020-01-25
    N.L. Savchenko; Yu.A. Mirovoy; A.S. Buyakov; A.G. Burlachenko; M.A. Rudmin; I.N. Sevostyanova; S.P. Buyakova; S.Yu. Tarasov

    The objective of this work was to study adaptive mechanisms and behavior of ZrB2-20 vol.% SiC ultra high-temperature ceramics in low-speed and high-speed sliding against a high-speed steel disk. The worn surfaces of ceramic samples were examined and characterized for chemical composition and mechanical properties. Intense tribooxidation of the composite components as well as transfer layer generation was observed at sliding speeds as high as 11 m/s, 22 m/s and 37 m/s with the formation of at least two subsurface layers. The first one was a mechanically mixed (transfer) layer composed of an iron-containing borosilicate glass mixed with the tribooxidation products resulted from oxidizing both ceramics and steel components. The second underlying layer was a partially oxidized zirconium diboride. Such a combination of quasi-viscous transfer layer and partially ductile underlying layer allowed reducing friction, forming a smooth worn surface and protecting the ceramics against brittle subsurface fracture. Also the effect of self-healing of the subsurface defects by means of liquid borosilicate glass was observed during sliding friction. The results obtained were discussed in comparison to other adaptation mechanisms found in different materials during friction.

  • Experimental analysis of the wear coefficient of double-nut ball screws
    Wear (IF 2.95) Pub Date : 2020-01-24
    Chang-Guang Zhou; Hua-Xi Zhou; Hu-Tian Feng

    The wear coefficient is an important parameter that directly determines the wear rate of ball–raceway contact in ball screws and thus affects the degradation of the accuracy of ball screws and computer numerical control machine tools. However, few studies have experimentally studied the wear coefficient of ball screws. The present paper proposes a model for calculating the wear coefficient by considering the wear mechanism at the ball–raceway contact in ball screws. More importantly, a novel test method is implemented to measure the wear coefficient of seven double-nut ball screws, with total running of 48 million revolutions. Experimental results show two obvious wear stages and give wear coefficients that are several orders of magnitude lower than the empirical wear coefficient for continuous sliding friction between steel and steel, mainly owing to the special motion and wear mechanism of ball screws. The findings are important to the study of the degradation of the performance of ball screws due to wear.

  • Effect of temperature on wear mechanisms of an aluminium - Based abradable coating for aircraft engines after a dynamic interaction with a Ti6al4v blade
    Wear (IF 2.95) Pub Date : 2020-01-23
    Baptiste Martinet; Andrea Cappella; Sylvain Philippon; Claudio Montebello

    Small blade-casing clearances in aircraft engines reduce fuel consumption but increase the risks of contact interactions due to working conditions. These interactions cannot be avoided but their effects can be reduced by using abradable linings thermally sprayed inside the casings. To investigate these interactions and the mechanisms of wear deriving from them, a specific ballistic bench has been developed in order to perform representative tests of the low-pressure compressor environment (up to 270 °C) and enabling only one interaction between an aluminum-based abradable sample and a Ti6Al4V tool. Contact forces and incursion depth were measured for a nominal depth of cut of 100 μm and at a mean velocity of 125 m/s. It has been shown that the temperature affects mainly the abradable behaviour under these high-speed interactions. In addition, the wear resulting at high temperature is driven by a process that can be very different from the low temperature case.

  • Martensitic wear resistant steels alloyed with titanium
    Wear (IF 2.95) Pub Date : 2020-01-22
    A.G. Kostryzhev; C.R. Killmore; D. Yu; E.V. Pereloma

    The traditional approach to improving the abrasion wear resistance of martensitic steels is to increase their hardness via high carbon levels. However: (i) a higher hardness is usually accompanied by a lower toughness, negatively affecting the impact wear resistance, and (ii) increased carbon concentrations reduce weldability and complicate thermal cutting. This work explored microalloying with Ti as a method to simultaneously increase hardness and toughness via a concurrent precipitation of coarse TiMoVCN, fine TiC and fine Fe3C particles. Five plate steels containing <0.4C, <0.8Ti, Mn, Si, Cr, Mo and V (wt. %) were melted, cast, hot forged and heat treated to replicate an industrial processing technology. Dependences of mechanical properties on steel composition were studied using hardness, tensile, Charpy impact, pin-on-drum wear (two-body abrasion wear conditions) and impeller wear (two-body impact wear conditions) testing. Microstructure characterisation was carried out using optical and scanning electron microscopy. With an increase in Ti/C ratio: hardness and strength showed a dependence with a maximum; toughness a dependence with a minimum; and wear resistance (both abrasion and impact) a dependence with a maximum. The maximum wear resistance (at Ti/C = 0.314) did not correspond to either hardness (at Ti/C = 0.905) or toughness (at Ti/C = 0.018) maximum, but matched the highest tensile strength. The fracture development at the particle-matrix interface was found to govern the wear mechanism in the studied steels.

  • Experimental investigation of fretting wear of coated spring clip and inlet ring in land-based gas turbines at elevated temperature
    Wear (IF 2.95) Pub Date : 2020-01-22
    Akshat Sharma; Farshid Sadeghi; Atin Sharma

    The objectives of this investigation were to characterize the friction and fretting wear behavior of coated inlet ring and spring clip components used in land-based gas turbines at elevated (500 °C) temperature. In order to achieve the objective, a novel high temperature fretting wear apparatus (HTFWA) was designed and developed to simulate the conditions existing in a gas turbine. Sections of actual inlet ring and spring clip were cut from a gas turbine and used in the test apparatus. The test apparatus was used to investigate fretting wear of APS sprayed Cr3C2–NiCr (25% wt.), HVOF sprayed Cr3C2–NiCr (25% wt.), HVOF sprayed T-800 and APS sprayed PS400 coated inlet rings against HVOF sprayed Cr3C2–NiCr (25% wt.) coated spring clip. Fretting wear experiments were conducted with normal loads up to 400 N at a fixed displacement amplitude of 0.5 mm and frequency of 5Hz. A proximity probe was used for in-situ wear depth measurement at the spring clip and inlet ring contact pair. The results indicate that the combination of PS400 coating on inlet ring and HVOF Cr3C2–NiCr on spring clip wear the least as compared to other combinations in both running-in condition and under steady state regime. PS400 also demonstrated a 50% reduction in coefficient of friction as compared to other coatings at 500 °C. Further, a theoretical approach was developed to estimate the evolution of wear depth with sliding distance for a cylindrical contact configuration using Archard's wear law. The experimental and theoretical results were found to be in good agreement with each other.

  • Chip formation and tribological behavior in high-speed milling of IN718 with ceramic tools
    Wear (IF 2.95) Pub Date : 2020-01-21
    F. Molaiekiya; M. Aramesh; S.C. Veldhuis

    Advanced ceramics exhibit excellent mechanical properties at elevated temperatures suggesting them as plausible cutting tool materials for machining of heat-resistant superalloys. However, despite numerous efforts to date, relative brittleness of ceramic tools can result in chipping or catastrophic failure, especially during an intermittent process where excessive thermo-mechanical alteration occurs, like high-speed face milling. Previous studies by the authors revealed that in high-speed milling of inconel with SiAlON tools, after surpassing a certain cutting speed where extreme levels of strain rates and temperatures exist, the IN718 machinability transforms drastically, showing a significant reduction in cutting force, chipping and tool wear. Following this observation, in the current paper, an attempt has been made to further investigate the phenomena acting at the shear deformation zones through analysis of chip formation mechanisms and tool-workpiece tribosystem. Numerous characterization techniques have been used in this research, such as cutting force measurements, chip cross-section studies, SEM/EDS, TEM, and nanoindentation. Results suggest that a reduction in material flow strength occurs at the extreme conditions of the cut, showing similarities to fluid flow in TEM images of the tool face. Increasing the cutting speed generally facilitates chip formation; However, a rise in cutting force by further increasing the speed, and excessive generation of unstable built-up layers practically limits the cutting speed. Additional XPS studies show that variation in cutting speed also changes the frictional response of the tool-workpiece tribosystem by forming lubricious and thermal-barrier tribofilms.

  • Ultrasonic surface treatment for improving wind-blown sand erosion resistance of cementitious materials
    Wear (IF 2.95) Pub Date : 2020-01-21
    Y. Shi; Z.M. Shi

    In this study, we present a method that employed ultrasound to impose vibration on the surfaces of cementitious materials at the early stage of hydration to form a hardening layer and improve the surface hardness. The formation mechanism of the ultrasonic hardening layer (UHL) was analyzed, and the density and surface hardness of the UHL were measured. An experimental study was carried out to determine the effect of the UHL on improving the wind-blown sand erosion resistance of cementitious materials. Experimental data show that the UHL has a density 3.3% greater and a hardness 136% greater than that of the contrast samples after 28-days of curing. Wind-blown sand erosion tests data show that to the specimens with 28-days curing age, the UHL can improve the erosion resistance for 12.8–24.1% versus that of the contrast in a 30-min erosion procedure.

  • High performance polymer composites - Influence of processing technique on the fiber length and performance properties
    Wear (IF 2.95) Pub Date : 2020-01-19
    Umesh Marathe; Jayashree Bijwe

    High performance polymer composites, (especially short fiber reinforced) have gained immense importance in the field of tribo-materials, especially for dry bearings. Among various key parameters controlling the final performance, the processing technique is the one, which is least investigated. Injection molding leads to a uniform dispersion and distribution of fibers but at the cost of an excessive reduction in the aspect ratio of fibers. Compression molding of short fibers retains their aspect ratio to a greater extent, but at the cost of inefficient dispersion of fibre strands. Interestingly, both the factors viz. High aspect ratio of fibers and excellent dispersion are important for deciding the performance of composites. In this work, two composites (Poly aryl ether ketone - 50 wt%, short glass fibres (length – 3 mm)– 30 wt % and synthetic graphite - 20 wt%) were molded by injection (I) and compression (C) molding. These were tribo-investigated in adhesive and abrasive wear modes in identical conditions. Based on thermal degradation of composites at 600 °C, the final fibre length was observed as 200–300 μm and 1.5 mm for I and C composites respectively. Both the composites showed low specific wear rate (K0) (∼10-16 m3/Nm) and coefficient of friction (μ) (∼0.03–0.05). Similarly, for abrasive wear, K0 and μ were observed ∼10-10 m3/Nm and ∼0.5–0.7 respectively. μ of I composite was lower in all conditions. The composite C was superior to the I in wear performance in adhesive wear, but not in abrasive wear. Worn surface analysis was done to understand the wear mechanisms.

  • Analytical wear model and its application for the wear simulation in automotive bush chain drive systems
    Wear (IF 2.95) Pub Date : 2020-01-16
    Robert Tandler; Niels Bohn; Ulrich Gabbert; Elmar Woschke

    The wear of automotive chain drive systems after high mileages is numerically calculated based on Fleischer’s energetic wear equation. This equation is embedded in a FE-model, consisting of one single chain link only. Their time-variant positions and acting forces are taken from a multi-body simulation. A focus is on ensuring the quality of the FE-model and the contact between pin and bush, where here a penalty approach has provided a stable solution schema. The parameters of the wear model are derived from measurements. After each time increment the wear results in a changed surface geometry, which is used for the simulation of the next time increment. The enormous computation time is reduced by the development of a convenient extrapolation factor. The complex simulation approach is applied to the chain drive of a test vehicle after a mileage of about 50000 km. The comparison of the simulated and measured data demonstrates an agreeing correlation.

  • Analysis and prediction of TBM disc cutter wear when tunneling in hard rock strata: A case study of a metro tunnel excavation in Shenzhen, China
    Wear (IF 2.95) Pub Date : 2020-01-16
    Weilin Su; Xinggao Li; Dalong Jin; Yi Yang; Ruicheng Qin; Xuyang Wang

    Disc cutter wear is the result of dynamic contact and friction between the tools and rocks in tunnel boring machine (TBM) tunneling. It can lead to a reduction in excavation efficiency, disruption of construction schedules, and extra costs. The geological indices, such as uniaxial compressive strength (UCS), Brazilian tensile strength (BTS) and Cerchar abrasion index (CAI), and the tunneling parameters, such as advance rate and rotation speed, were collected in the Shenzhen metro tunnel excavation project, and they have major effects on the cutter consumption rate. The wear data of 871 disc cutters over a 1592 m-long advance distance were analyzed. It was found that 87% of the disc cutters used were replaced due to normal wear, and the others were replaced due to abnormal wear. Flat wear mainly occurs for the disc cutters in the central area of the cutterhead, because they have a larger rotational resistance and eccentric loading due to their smaller rotational radius. The abnormal wear of the outer-area disc cutters mainly consists of forms of cutter ring cracking and bearing crushing owing to a higher rotation speed. A disc cutter wear prediction model was established to estimate the disc cutter consumption based on the plastic removal abrasiveness and motion analysis of the cutter rings. A rough linear correlation between the cumulative wear depth and the advance distance is found, and the wear rate varies during the tunneling progress due to the different geotechnical or construction parameters. The predicted wear is generally less than the actual wear, and the maximum prediction error is 49.4 mm. The predicted error is always larger for the disc cutters that have a high probability of non-uniform wear, especially for those in the outer area.

  • Wheel slip/Slide and low adhesion caused by fallen leaves
    Wear (IF 2.95) Pub Date : 2020-01-16
    H. Chen; T. Furuya; S. Fukagai; S. Saga; J. Ikoma; K. Kimura; J. Suzumura

    On the sloping section of a train service line located in mountainous areas, idling and skidding of the wheels caused by leaves that fall on the railhead in autumn often occurs, and this hinders the scheduled operation of the train. Although countermeasures such as spraying sand or ceramic particles onto the contact zone of wheel/rail are adopted, the effect is insufficient in late autumn. For clarifying the mechanism of the decrease in the adhesion between the wheel and the rail based on fallen leaves and acquiring information useful for practical implementation of countermeasures, the authors conducted a vehicle running test with driving and braking operations on a test line to investigate the occurrence of wheel slipping/sliding under various railhead states such as dry/wet leaves and dry/wet black accretion films, as well as the adhesion coefficient between the wheel and the rail when dry/wet black accretion films exist on the railhead. The results clarified that the wheel slipping/sliding was likely to occur under wet conditions, in particular frequently occur while wet black accretion films exist on the railhead, and then a low adhesion coefficient was recognized under the same conditions. Regarding the black accretion film formation process, the authors reproduced by a rail cooling device which can simulate atmospheric temperature in mountain area, and clarified that the tannin contained in the crushed fallen leaves has a reaction with steel comment of rail under wet (condensation, frost, light rain etc.) conditions and then black tannin iron was generated and adhere to the railhead. The countermeasure of wheel slip/slide should be focused on how to prevent the formation of the black accretion films or remove the black accretion films in the future work.

  • Effects of Co and W on the microstructure and wear behavior of NiCrAlMoTiFeNbX equimolar multicomponent-clad layers
    Wear (IF 2.95) Pub Date : 2020-01-11
    Yuan-Ching Lin; Yu-Yu Liu

    In this study, we used the gas tungsten arc welding (GTAW) process for cladding NiCrAlMoTiFeNbCo and NiCrAlMoTiFeNbW multicomponent alloys onto the surface of AISI 1020 low-carbon steel. The microstructures and the sliding wear resistance of the cladding layers were characterized. The experimental results indicated that a multiple-carbide particle composed of (Nb,Ti)C with a TiC-rich core and NbC shell, was synthesized in situ in both multicomponent cladding layers. The eutectic phase of Fe0.875Mo0.125 with the body-centered cubic structure (BCC) was present in the NiCrAlMoTiFeNbCo cladding layer, and the reinforcing phase of Fe2W with the hexagonal-closest-packed (HCP) structure was in the NiCrAlMoTiFeNbCW cladding layer. Wear test results revealed that the wear performance of the multicomponent cladding layers can significantly improve the wear resistance of the AISI 1020 low-carbon steel. The wear resistance of the NiCrAlMoTiFeNbW cladding layer exceeded that of the other cladding layer. The improvement in the wear resistance of the NiCrAlMoTiFeNbW cladding layer was attributable to the high hardness of the cladding layer and the Fe2W reinforcement in the cladding layer. The wear test results confirmed that the cladding layer with higher ratios of hardness to Young's modulus for both the matrix and the strengthening phase exhibited better wear resistance.

  • A study of Cr3C2-based HVOF- and HVAF-sprayed coatings: Abrasion, dry particle erosion and cavitation erosion resistance
    Wear (IF 2.95) Pub Date : 2020-01-11
    V. Matikainen; H. Koivuluoto; P. Vuoristo

    Material and spray process selection are the key factors in the tailoring of thermal sprayed coatings for demanding industrial applications. In this study, four commercial Cr3C2-based feedstock materials were sprayed with gas-fuelled high-velocity oxygen-fuel (HVOF) and modern high-velocity air-fuel (HVAF) spray processes. Two materials with standard Cr3C2–25NiCr composition (porous and dense), a Cr3C2–50NiCrMoNb and Cr3C2–37WC–18NiCoCr materials were sprayed in addition to the reference WC-10Co4Cr material. The Cr3C2–50NiCrMoNb had a higher content of the Ni-based metal matrix compared to standard Cr3C2–25NiCr composition for added corrosion resistance, while the Cr3C2–37WC–18NiCoCr material contained additional tungsten carbide (WC) particles to improve the wear resistance. In abrasion and dry particle erosion, the Cr3C2–50NiCrMoNb coatings showed a higher degree of plastic deformation and increased material loss, whereas the Cr3C2–37WC–18NiCoCr coating had wear resistance between the standard Cr3C2–25NiCr and reference WC-10Co4Cr coatings. In cavitation erosion, the lower carbide content of Cr3C2–50NiCrMoNb coatings turned out to improve the resistance against fatigue wear due to higher fracture toughness. Overall, the HVAF sprayed coatings had higher elastic modulus, higher fracture toughness, equal or higher abrasion and erosion resistance, and higher cavitation erosion resistance compared to the HVOF sprayed counterparts.

  • On the impacts of grain refinement and strain-induced deformation on three-body abrasive wear responses of 18Cr–8Ni austenitic stainless steel
    Wear (IF 2.95) Pub Date : 2020-01-08
    C.Y. Hu; X.L. Wan; K.M. Wu; D.M. Xu; G.Q. Li; G. Xu; R.D.K. Misra

    The concept of phase reversion annealing involving cold deformation of metastable austenite to strain-induced martensite, followed by annealing was adopted to obtain fine grained 18Cr–8Ni austenitic stainless steel. The primary objective of the present study was to elucidate the wear performance of fine-grained austenitic stainless steel through three-body abrasive wear tests at room and high temperatures and compare with the coarse-grained counterpart. The quartzite stones (quartz content over 90 wt%) with diameter 5–15 mm and hardness of 1100HV were used as the abrasive in three-body abrasive wear tests. The study demonstrated that the microstructure consisting of near defect-free and equiaxed fine austenite grains with high yield strength and elongation exhibited superior wear resistance at high temperature (250 °C), which is attributed strain-induced deformation in fine austenite grains. The wear mechanism varied as a function of distance from the center of the steel sample and was characterized by microploughing and microcutting.

  • Influence of surface roughness and phosphate coating on galling resistance of medium-grade carbon steel
    Wear (IF 2.95) Pub Date : 2020-01-03
    B. Podgornik; F. Kafexhiu; A. Nevosad; E. Badisch

    The aim of this research work was to investigate the influence of surface roughness and presence of phosphate coating on the galling resistance of medium-grade carbon steel. Galling resistance was evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation, surface quality, and volume of adhered material, analysed by load-scanner test rig as a function of load. Results of the investigation show that best galling resistance is not provided by very smooth surfaces but with semi rough ones (Ra = 0.21–0.28 μm), obtained by fine turning. Furthermore, by phosphating and formation of low-friction Mn–P coating superior galling resistance for medium-grade carbon steel is provided, at the same time diminishing effect of surface roughness.

  • Casting temperature dependent wear and corrosion behavior of 304 stainless steel reinforced A356 aluminium matrix bimetal composites fabricated by vacuum-assisted melt infiltration casting
    Wear (IF 2.95) Pub Date : 2020-01-03
    Ridvan Gecu; Ahmet Karaaslan

    This study aims to determine optimum casting temperature to achieve maximum wear and corrosion resistance in 304 stainless steel (SS) reinforced A356 matrix bimetal composites, which have been developed for use where conventional ceramic reinforced metal matrix composites have been used. Vacuum-assisted melt infiltration casting technique was used to manufacture bimetal composites at the various casting temperatures from 630 °C to 880 °C. The composite samples were subjected to dry sliding ball-on-disc tests using Al2O3 ball and immersion test in 3.5% NaCl solution for 7–21 days. θ (Fe4Al13) and η (Fe2Al5) phases developed at A356/304 interfaces and thickened with increasing temperature. Abrasion and adhesion as predominant wear mechanisms were observed in worn surface examinations, while pitting and galvanic corrosion occurred in corroded surfaces. The most suitable casting temperature was found to be 730 °C, considering the wear and corrosion properties of produced bimetal composites under certain conditions.

  • A high-performance copper-based brake pad for high-speed railway trains and its surface substance evolution and wear mechanism at high temperature
    Wear (IF 2.95) Pub Date : 2020-01-02
    Peng Zhang; Lin Zhang; Dongbin Wei; Peifang Wu; Jingwu Cao; Cairang Shijia; Xuanhui Qu

    High temperature is one of the most basic challenges faced by copper-based brake pads in emergency braking of high-speed railway train. Here, a novel copper-based brake pad was prepared and its tribological properties in the temperature ranging of 400–800 °C were studied by pin-on-disc tribometer equipped with heating chamber. The results show that compared with commercial copper-based brake pad, self-designed copper-based brake pad exhibits higher mean friction coefficient and smaller fluctuation of friction coefficient under all test conditions. The friction coefficient of self-designed copper-based brake pad is in the range of 0.35–0.45 at the temperatures up to 600 °C. At 800 °C, the failure mechanism of copper-based brake pad is related to the properties of graphite and copper. Graphite on the friction surface disappears after severe oxidation, resulting in the loss of lubrication of friction interface. Copper undergoes oxidation and softening. Oxidation makes copper unable to promote the formation of stable tribo-film, and the low-strength copper matrix after softening cannot effectively support the friction surface. Therefore, one of the key principles to design high-performance copper-based brake pad is to increase the oxidation resistance of graphite and the high temperature strength of copper matrix.

  • Complex eigenvalue analysis and parameters analysis to investigate the formation of railhead corrugation in sharp curves
    Wear (IF 2.95) Pub Date : 2019-12-28
    O. El Beshbichi; C. Wan; S. Bruni; E. Kassa

    Rail corrugation, a quasi-sinusoidal irregularity of the rail head, is a common issue experienced throughout the railway networks worldwide. It generally leads to high wheel-rail dynamic loads, increased noise emission, and poor ride comfort. Most commonly, rail corrugation is likely to develop on sharp curves. This paper aims to study the numerical feasibility of the prediction of self-excited vibrations for the study of rutting corrugation formation without excitation from initial rail roughness. A finite element model for the prediction of the self-excited vibrations of the leading wheelset-rails system in a sharp curve has been developed in ABAQUS. The friction coupling between the wheel and rail is taken into account. It is assumed that the lateral creep forces between wheel and rail are quasi-saturated. The proposed model is applied to investigate the effect of several structural factors on self-excited vibrations occurrence. The obtained numerical results match closely with the typical wavelength of rutting corrugation observed in the field sites and the experimental evidence on rutting corrugation. It has been found out that the interaction effect of the wheelset cross-section and the track gauge has a significant influence on self-excited vibrations. For a typical European wheelset cross-section, self-excited vibrations only occurred under the widened track gauge. For the studied Chinese wheelset, self-excited vibrations occurred, however, only under the standard track gauge. Therefore, following the assumptions underlying the analysis, wheelset cross-section might be an inhibitor factor at a particular track gauge. A parameter sensitivity analysis shows that the friction coefficient is linearly correlated with the system's instability and the frequency of the unstable modes of vibration.

  • Microstructures and intrinsic lubricity of in situ Ti3SiC2–TiSi2–TiC MAX phase composite fabricated by reactive spark plasma sintering (SPS)
    Wear (IF 2.95) Pub Date : 2019-12-28
    Carl Magnus; Daniel Cooper; Le Ma; William M. Rainforth

    MAX phase composite Ti3SiC2–TiSi2–TiC based on the Tin+1SiCn system was synthesized by spark plasma sintering (SPS) under vacuum sintering conditions. The microstructural evolution upon synthesis and Vickers indentation contact damaged were characterized using scanning electron microscopy (SEM) and optical microscopy (OM). Tribological behaviour of the SPSed MAX phase composite was investigated under dry sliding ambient conditions for evidence of intrinsic lubricity as well as to understand the influence of second phase TiC particles on the wear behaviour of this composite system. Further, the underlying wear mechanisms was elucidated via detailed analyses of the worn surfaces using Raman spectroscopy, SEM-EDS and transmission electron microscopy (TEM). Exhaustive analyses of the worn surface revealed evidence of solid lubrication. Transition in friction and wear is attributed to change in wear mechanism from tribo-oxidative to deformation-induced wear due to the disruption of the tribofilm architecture.

  • A new generalized philosophy and theory for rubber friction and wear
    Wear (IF 2.95) Pub Date : 2019-12-27
    Y. Fukahori; P. Gabriel; H. Liang; J.J.C. Busfield
  • Tailoring of surface topography for tribological purposes by controlled solid particle impacts
    Wear (IF 2.95) Pub Date : 2019-12-26
    Melentiev Ruslan; Fengzhou Fang

    This study proposes a novel, cost-efficient and productive technique, Tribo-blast, to tailor surface topography for tribological purposes. Tribo-blast is based on mask-less micro-blasting with spherical or angular particles and precisely controlled process parameters. This approach enables rapid fabrication of μ-pockets (5–50 μm) on free-form surfaces comprised of any material. A particle with a new 3D geometry—a spinning top—is proposed to match the shape and dimensions of the irregular craters formed in a metallic target by an angular particle at the normal impact angle. The results were experimentally validated on stainless steel 316L, Co–Cr–Mo and Ti–6Al–4V alloys. A simple analytical routine allowed for control over the size, area, concentration and homogeneity of randomly distributed angular and spherical μ-pockets with <20% error. The Abbott-Firestone curve and texture ratio can be tailored according to one's intended design. The bearing index of the tailored surface was more than two times that of the lapped surface, and fluid retention was increased one hundred times. Thus, this approach is considered to be more productive, cost-effective and simple than current micro-texturing techniques.

  • Erosion analysis of machine gun barrel and lifespan prediction under typical shooting conditions
    Wear (IF 2.95) Pub Date : 2019-12-26
    Xiaolong Li; Yong Zang; Lei Mu; Yong Lian; Qin Qin

    The operational lifespan of a conventional weapon, such as artillery or machine gun, highly depends on the performance of its barrel. The bore of a machine gun is exposed to erosion as the number of rounds fired increases, which results in continuous increases in barrel diameter and thus an undesired degradation in ballistic performance. In this study, a critical isothermal erosion model for a machine gun barrel is established, and a numerical simulation method is used to study the bore erosion under typical shooting conditions. The current study confirms the presence of thermal-chemical erosion as a predominant failure mechanism at the starting point of the barrel rifling. It is also noted that this thermal-chemical erosion zone expands with the increase in the number of shots fired. Increases in firing frequency, and ambient temperature, and a decrease in the interval between cartridges are found to aggravate the erosion of the barrel bore. By fitting the calculated results, a formula for predicting the maximum erosion at the starting point of the barrel rifling is constructed. The predicted results demonstrate acceptable deviations from the experimental ones, which verify the accuracy and feasibility of the newly developed method in predicting machine gun barrel lifespan.

  • Friction and wear performance of sliding bearing seat of reactor pressure vessel
    Wear (IF 2.95) Pub Date : 2019-12-24
    Lanwen Wang; Xuanyu Sheng

    This paper systematically studies the friction and wear properties between the friction plates and the support platform of the marine nuclear power plant reactor. The friction performance between SA508 steel and three different kinds of graphite is studied with a commercial reciprocating sliding friction and wear tester. The variation of friction coefficient of materials under different temperature and load is analyzed, and the wear mechanism is analyzed to decide whether these graphite materials can be applied to marine nuclear power station. The results show that in this experiment, the change trend of friction coefficient with time is increasing at first, then decreasing and finally increasing slowly; and the higher the temperature, the larger the friction coefficient; the larger the load, the smaller the friction coefficient. The wear rate of graphite materials increases with temperature and load. The wear mechanism of the material under low temperature and low load is mainly adhesion wear, accompanied by a small amount of abrasive wear, and as the temperature increases and the load increases, the abrasive wear will increase. The friction coefficient of the material exceeds the predetermined value under a certain temperature or load, so it cannot be applied to a marine nuclear power plant.

  • Wear reduction mechanisms within highly wear-resistant graphene- and other carbon-filled PTFE nanocomposites
    Wear (IF 2.95) Pub Date : 2019-12-24
    Suvrat Bhargava; Mary E. Makowiec; Thierry A. Blanchet

    In recent years, a few select carbonaceous fillers with nanometer-size dimensions, such as graphene platelets, activated carbon nanoparticles and carbon nanotubes, have been shown to reduce the wear rates of PTFE to levels approaching 10−7 mm3/Nm and below. X-ray diffraction (XRD) and attenuated total reflectance (ATR) mode IR spectroscopy are used to show that these highly effective fillers provide wear resistance to PTFE through shared mechanisms. These mechanisms are also shown to operate in highly wear-resistant composites of PTFE with nanometer-sized particles of α-phase alumina. Addition of these highly effective fillers to PTFE results in a greater resemblance of the crystalline structure of PTFE at room temperature with a tougher and higher temperature phase. When slid against steel countersurfaces under ambient conditions, these fillers embedded within the PTFE matrix also enable the formation of robust transfer films through the formation of metal chelates.

  • Wear performance investigation of PVD coated and uncoated carbide tools during high-speed machining of TiAl6V4 aerospace alloy
    Wear (IF 2.95) Pub Date : 2019-12-24
    M.S.I. Chowdhury; B. Bose; K. Yamamoto; L.S. Shuster; J. Paiva; G.S. Fox-Rabinovich; S.C. Veldhuis

    Selection of hard PVD coatings for the machining of Ti6Al4V alloy should be based on the dominant tool wear mechanism and tribological phenomena occurring at the chip-tool-workpiece interface. The present work investigates the effect of AlTiN and CrN hard coatings on the wear performance of cemented carbide cutting tools during high-speed finish turning of Ti6Al4V. The wear characteristics of the tools were evaluated by SEM and 3D wear volume measurements. The in-situ tribological performance of the coatings was characterized by chip morphology analysis, in combination with coefficient of friction measurements using a high temperature/heavy load tribometer that mimics actual machining conditions. Micro-mechanical characteristics of the coatings were also studied in detail. The results obtained show that the application of a CrN coating significantly improves tool performance due to a combination of the micro-mechanical properties of the coating and the tribological characteristics of the surface engineered layer.

  • Effect of electrical current density, apparent contact pressure, and sliding velocity on the electrical sliding wear behavior of Cu–Ti3AlC2 composites
    Wear (IF 2.95) Pub Date : 2019-12-23
    Hao Zhao; Yi Feng; Zijue Zhou; Gang Qian; Jingcheng Zhang; Xiaochen Huang; Xuebin Zhang

    The purpose of this research was to investigate the potential use of Cu–Ti3AlC2 composites sliding against a Cu–5%Ag alloy as a viable electrical contact couple. Sliding friction and wear tests were conducted in the presence of an electric current using a custom-designed block-on-ring wear testing apparatus. The electrical current density was 0-15 A/cm2 along with an apparent contact pressure of 1.25-7.5 N/cm2 and sliding velocities ranging from 2.5 to 15 m/s. The results indicate that friction coefficient, wear rate, and contact voltage drop measured for the sliding couple increases with an increase in the electrical current density. As the apparent contact pressure increases, the contact voltage drop of Cu–Ti3AlC2 composites increases gradually, while friction coefficient and wear rate first decrease and then increase. With an increase in the sliding velocity, the friction coefficient of the sliding pair decreases and the contact voltage drop increases gradually, while wear rate decreases first, then increases. Adhesive wear and arc erosion wear proposed as the main wear modes. A lubricating film was observed to form on the wear surfaces under each test condition, and that film apparently improves the tribological properties of the sliding couples.

  • The wear behaviour of remineralised human dental enamel: An in vitro study
    Wear (IF 2.95) Pub Date : 2019-12-21
    Joseph A. Arsecularatne; Mark J. Hoffman

    This paper investigates the wear behaviour of remineralised human dental enamel. Polished enamel flat surface samples were first demineralised in an acid solution and then remineralised in whole human saliva. They were opposed by enamel cusps in wear tests. Wear depth was measured by a profilometer and the wear surface and subsurface were examined by electron microscopy. The results show that the pores in the top surface layer collapse during wear and form a particle layer which is subsequently removed by ploughing/delamination. For enamel underneath, the dominating wear mechanism is delamination. Remineralised enamel is extremely vulnerable since the measured wear is approximately four times that for sound enamel.

  • Efficacy of surface microtexturing in enhancing the tribological performance of polymeric surfaces under starved lubricated conditions
    Wear (IF 2.95) Pub Date : 2019-12-19
    Reza Gheisari; Pixiang Lan; Andreas A. Polycarpou

    The efficacy of microtexturing on the tribological performance of Aromatic Thermosetting CoPolyester (ATSP) and Ultra High Molecular Weight Polyethylene (UHMWPE) were investigated under oil-lubricated starved conditions. Nominal contact pressures of 5.02 and 10.04 MPa were applied over a range of sliding velocities, 0.008–2.278 m/s. Static and kinetic coefficients of friction (COF) for untextured and textured surfaces were obtained and compared. Reduction in the average kinetic COF up to 29% for microtextured ATSP and 25% for microtextured UHMWPE were obtained. Static COF did not exhibit a notable change as a result of microtexturing. The core void volume was identified as a reliable indicator of the wear intensity of the dimples and consequently lubricant retention capacity for texturing. While both microtextured polymers illustrated reduction in the kinetic COF, only ATSP showed mechanical integrity for applications that experience high contact load under starved conditions. Microtextured UHMWPE experienced mechanical failure due to fluid pressure build up in the dimples under high load tests.

  • Measurement of fracture toughness of copper via constant-load microscratch with a spherical indenter
    Wear (IF 2.95) Pub Date : 2019-12-17
    Dong Zhang; Yuan Sun; Chenghui Gao; Ming Liu

    Fracture toughness can be measured by microscratch test from objective force and depth measurement, which is much convenient than indentation approach and conventional means, since initial notch or pre-crack is not required. Micro-scratch test was conducted on copper under a spherical probe of radius 105 μm and constant applied normal load with the aim of characterizing fracture toughness of copper by sliding technique with a sphere. Scratch variables such as normal load, lateral load, friction coefficient, and penetration depth were analyzed, and different methodologies for calculating fracture toughness were compared. Linear elastic fracture mechanics was found to be inapplicable to scratch of elastic-plastic material with sufficient plasticity under a spherical probe, while energetic size effect law can be successfully applied to characterize fracture toughness by microscratch test with a sphere abrading metallic material.

  • Wear minimization for highly loaded iron-based MMCs due to the formation of spongy-capillary texture on the friction surface
    Wear (IF 2.95) Pub Date : 2019-12-17
    Eugene E. Feldshtein; Larisa N. Dyachkova

    Worn surfaces of a wide range of metal matrix composites (MMCs) produced by various technologies were analyzed. High-resolution scanning electron microscope images at magnifications exceeding 3000 times were used for the analysis. This research considers the problem of formation of a specific spongy-capillary texture on friction surfaces of highly loaded iron-based MMCs. The texture provides a significant improvement of wear resistance. It was also found that the worn surfaces contain oil molecules in the iron matrix micropores as well as the copper phase or reinforcing particulates. MMCs components are transferred to the friction layer on the counter-body during friction. Interaction of the friction pair elements enhances a quick and effective running-up ability.

  • Experimental and FEM analysis of mar behavior on amorphous polymers
    Wear (IF 2.95) Pub Date : 2019-12-12
    Shuoran Du; Marouen Hamdi; Hung-Jue Sue

    Mar is a type of subtle surface damage caused by a sliding object barely visible to human eyes. This minor damage phenomenon has rarely been systematically studied. Significant research efforts for the fundamental understanding of mar behavior in polymers are still needed. In this study, the mar behavior of a series of model amorphous polymers, i.e., polymethylmethacrylate (PMMA), polycarbonate (PC), and polystyrene (PS), were investigated based on a modified ASTM/ISO scratch testing methodology and a corresponding finite element method (FEM) modeling. Furthermore, the mar-induced visibility and material parameter relationships were established through a systematic FEM parametric study. Experimental results show that PMMA has the highest mar visibility resistance, indicated by lower surface roughness variation and low contrast between marred region and the background. The numerical analysis showed that the maximum plastic principal strain (ε1p) and total dissipated plastic energy (Ep) can be considered for evaluating mar visibility resistance. Higher mar visibility resistance corresponds to lower ε1p and Ep values. Based on these two criteria, the parametric analysis shows that mar visibility resistance increases with lower modulus, higher yield stress, higher hardening slope, and lower softening slope. The usefulness of the present study for the preparation of mar resistant polymers is discussed.

  • A pin-on-disc study on the dry sliding behavior of a Cu-free friction material containing different types of natural graphite
    Wear (IF 2.95) Pub Date : 2019-12-11
    Mara Leonardi, Mattia Alemani, Giovanni Straffelini, Stefano Gialanella

    This research investigates the influence of graphite's granulometry on the dry sliding behavior of a copper-free friction material against pearlitic cast iron. Samples were designed and fabricated using three different types of commercial natural graphite. A sample without graphite was also considered as a reference. Tests were carried out with a pin-on-disc tribometer at room temperature (RT), at 400 °C, and at RT after the high temperature tests. The results show that both the shape and size of the graphite particles influence the coefficient of friction and the specific wear rate. The friction material featuring a lower particle size and equiaxed grains of natural graphite exhibits a better behavior, as compared to coarser graphite with plate-like grains. The results were obtained comparing specific characteristics (i.e., morphology and chemical composition) of the friction layers formed on each friction material under the different testing conditions.

  • Effect of pre-wear on the rolling contact fatigue property of D2 wheel steel
    Wear (IF 2.95) Pub Date : 2019-12-09
    Chun-peng Liu, Peng-tao Liu, Jin-zhi Pan, Chun-huan Chen, Rui-ming Ren

    In this work, the effect of pre-wear under air condition on the rolling contact fatigue life (RCF) of D2 wheel steel under oil lubrication was thoroughly studied based on the rolling wear experiment. The results show that dry pre-wear can improve the RCF life of wheel sample under oil lubrication during RCF process before the sample surface forms the fatigue wear cracks during pre-wear process. Dry pre-wear can change largely pre-wear surface, such as increasing surface layer dislocation density, refining ferrite grains, dissolving lamellar cemetite in pearlite, forming fibrous microstructure and reducing surface roughness. These microstructural changes contribute to an improvement of the surface strength and RCF life of samples. However, when fatigue wear occurs on the contact surface during pre-wear process. The fatigue wear crack causes the flaking of hardening layer, and is a RCF crack source to accelerate the formation of the RCF crack. It can lead to reduce the RCF life of the sample.

  • Sediment erosion in low specific speed francis turbines: A case study on effects and causes
    Wear (IF 2.95) Pub Date : 2019-12-06
    Saroj Gautam, Hari Prasad Neopane, Nirmal Acharya, Sailesh Chitrakar, Biraj Singh Thapa, Baoshan Zhu

    Hydraulic turbines experience severe operational and maintenance challenges when operated in sediment-laden water. The combined effect of erosive and abrasive wear in turbine components deteriorates their life and efficiency. The quantity and pattern of sediment erosion depends on the nature of the flow and the amount of hard minerals contained in water. Localized erosion patterns are observed mostly in guide vanes, runner blades and facing plates of Francis turbines due to different natures of fluid flow in those regions. Accelerating flow around the guide vanes and its shaft causes abrasive and erosive wear in its surface, which causes increase in the size of the clearance gap between the facing plates and the guide vanes. Flow leaving the clearance gap forms a vortex filament due to the leakage from high pressure side to the low-pressure side of the guide vane, which eventually strikes the rotating runner blades. This paper presents a case study of a power plant in India with low specific speed Francis turbines, which is severely affected by sediment erosion problems. A numerical analysis of the flow is conducted inside the turbine to study the causes of various erosion patterns in the turbine components. The results from the CFD are compared with the actual erosion in the turbines. Erosion in guide vanes and runner blades are taken into consideration in this paper, due to the complex flow phenomena around these regions. It is found that the leakage flow through the clearance gaps of guide vanes is the primary cause of erosion at the inlet of the runner blades. Furthermore, the effects of size and shape of quartz particles are studied which shows that erosion is directly proportional to these parameters.

  • Understanding the influences of pre-corrosion on the erosion-corrosion performance of pipeline steel
    Wear (IF 2.95) Pub Date : 2019-12-06
    Yunze Xu, Liang Liu, Qipiao Zhou, Xiaona Wang, Yi Huang

    The initiation and the dynamic progression of erosion-corrosion on a pre-corroded X65 pipeline steel surface was investigated using coupon electrodes and wire beam electrode (WBE). Results show that a concentrated erosion-corrosion region would appear on the steel surface after pre-corrosion which is significantly different from the scatter distributed impingement craters on a fine polished steel coupon. The initiation of localized erosion-corrosion on a pre-corroded steel surface is most probably induced by the instant interfacial chemical and electrochemical heterogeneity, and the instantaneous inhomogeneous sand impingements rather than the surface roughness increasing and the porous rust layer. The pre-corroded area having an initial intense sand impingements would propagate to a concentrated low-lying erosion-corrosion area and small cathodic regions would propagate to isolated islands in the low-lying area.

  • Wear of form taps in threading of Al-Si alloy parts: Mechanisms and measurements
    Wear (IF 2.95) Pub Date : 2019-12-06
    Rohan Kumar Barooah, A.F.M. Arif, J.M. Paiva, Simon Oomen-Hurst, S.C. Veldhuis

    Wear of form taps in machining of Al-12Si die-cast alloys has been a critical problem for automotive engine manufacturing. Poor quality of formed threads results in high rework cost, and scrap. This research is focused on investigating the wear mechanisms and quantify wear by developing new measurement metrics. In addition, a performance criterion has been proposed to limit machining and evaluate wear on form taps. Abrasion and Adhesion wear mechanisms have caused severe deterioration of lobes on the chamfered length of tap tools during form tapping. A detailed evaluation of the complexity of wear propagation has been presented for critical regions of a lobe in a form tap.

  • Solid particle erosion behavior of laminated ceramic structures
    Wear (IF 2.95) Pub Date : 2019-12-02
    Goffredo de Portu, Paola Pinasco, Cesare Melandri, Claudio Capiani, Cristina Guardamagna, Lorenzo Lorenzoni, Federico Cernuschi

    Often ceramics employed for structural applications have to operate in harsh environments withstanding also solid particle erosion phenomena. Enhanced surface toughness and wear resistance of ceramic components can be achieved by laminated hybrid composites owing to the compressive residual stresses that can be generated into the surface by suitably combining the thermo-physical features of the different materials. In this work the superior solid particle erosion resistance of symmetrical Al2O3 and Al2O3–ZrO2 laminated composites compared to homologous Al2O3 bulk material has been experimentally assessed. Furthermore, based on the experimental results an heuristic solid particle erosion model able to correctly predict the erosion rate when testing conditions change has been proposed.

  • Performance and hydrodynamics analysis of a Toroid Wear Tester to predict erosion in slurry pipelines
    Wear (IF 2.95) Pub Date : 2019-11-27
    N.R. Sarker, D.E.S. Breakey, M.A. Islam, S. Sun, B.A. Fleck, R.S. Sanders

    Erosion analysis is crucial for the design, operation, and economic assessment of slurry pipelines. Since field-scale pipe tests are difficult to control, lab-scale experiments are frequently employed. However, these techniques produce hydrodynamic conditions dissimilar to pipe flow. The Toroid Wear Tester (TWT) is a lab-scale tester with several promising attributes, including hydrodynamics more similar to pipe flow than other wear testers. However, no detailed studies on TWT performance and hydrodynamics have been performed. This work evaluates the repeatability and parametric wear trends of a TWT, as well as the major differences between TWT and pipe-flow hydrodynamics. Different particle sizes (0.1–2 mm) were tested at varying speeds (1–3 m/s) and solids concentrations (5–30% by volume). Visualization experiments showed that only larger particle sizes or lower TWT speeds are suitable for generating sliding-bed-dominated erosion comparable to pipe flow. Visualizations are also used to obtain correction factors for the TWT data, showing that visualization is a critical component of TWT testing. In addition to previously observed particle–coupon contact time and particle degradation effects, normal load and coupon edge effects are identified as important. Despite these limitations, the TWT is a promising apparatus for ranking material wear resistance and, with careful interpretation, for making pipeline erosion predictions.

  • Research on synergistic lubrication effect of silver modified Cu–Ni-graphite composite
    Wear (IF 2.95) Pub Date : 2019-11-27
    Yiran Wang, Yimin Gao, Yefei Li, Mengting Li, Liang Sun, Wenyan Zhai, Kemin Li

    Cu–Ni-graphite composite is intended to be used as switch slide baseplates in the high-speed railways., The composite is modified by silver element to enhance the tribological properties. Pin-on-disk wear tests were conducted to evaluate the tribological properties. The synergistic lubrication effect generated when the silver-modified Cu–Ni-graphite composite slide against U75V steel. The results showed that the silver-modified Cu–Ni-graphite composite consists of α-Cu, graphite, and a silver phase. The higher graphite content in the composite corresponds to lower coefficient of friction and wear weight loss. Both the coefficient of friction and wear weight loss of the silver-modified composite are much lower than those of the unmodified Cu–Ni-graphite composite. The synergistic lubrication effect of graphite and silver in the composite decrease the friction coefficients and wear weight loss. Compared with the single graphite lubrication, the introduction of the silver phase efficiently enhances the lubricating property and decreases the microcutting and deformation effects. The wear mechanism of silver-modified Cu–Ni-graphite composite with 1–6 wt% graphite content consists of microcutting, oxidation wear, and adhesion wear. The delamination and fatigue wear are resisted at the higher graphite contents by the addition of the silver phase.

  • Wear analysis and prediction of rigid catenary contact wire and pantograph strip for railway system
    Wear (IF 2.95) Pub Date : 2019-11-26
    X.K. Wei, H.F. Meng, J.H. He, L.M. Jia, Z.G. Li

    With the rapid development of urban rail transit, the operation companies are plagued by the wear issue of metro pantograph-catenary (PAC) system in the last decades. Abnormal wear not only increases the maintenance cost but also seriously affects the stability and safety of the PAC system. In this paper, the models of calculating the wear rate are proposed in the first place, which can be used to approximately predict the wear of the contact wire (CW) and the pantograph strip (PS). After that, the wear distribution on the rigid catenary wire between two adjacent subway stations is analyzed. In addition, the layout of the CW is investigated and a calculation method for estimating and predicting the wear profile on the PS is proposed. The maintenance data recorded by GuangZhou Metro Line 2 and Beijing Metro Line 6 are introduced to validate the proposed models and prediction methods. It shows that the predicted results are in good consistency with the practical wear on the CW and also on the PS. With the help of the wear distribution on the CW, it provides with a reference to take effective measures to extend the service life of the CW and make a differentiated maintenance strategy. In the light of the proposed wear prediction method for PS, a more optimal layout of the CW can be designed to reduce the formation of deep grooves on the PS.

  • Understanding and treatment of squat defects in a railway network
    Wear (IF 2.95) Pub Date : 2019-11-26
    H. Zhu, H. Li, A. Al-Juboori, D. Wexler, C. Lu, A. McCusker, J. McLeod, S. Pannila, J. Barnes

    A comprehensive investigation of the Sydney Trains railway network has been carried out to control and minimize rail degradation, especially squat defects. Squat occurrence was analysed with respect to the parameters of traffic operation and track geometry. Detailed metallurgical examination of the ex-service rails revealed a possible connection between brittle White Etching Layers (WELs) and the occurrence of squats in the running band of the rail. Initiation of squats was found to be associated with the progression of surface cracks in the WELs. Furthermore, two distinguishable types of WELs were found, based on different track operational conditions. These are described as Thermally Produced WEL (TP-WEL) which was found in heavy braking regions, and Severe Deformation WEL (SD-WEL) which was found in track regions under steady traffic speeds. In addition to the explanations based on thermal phase transformation and severe plastic deformation, the arcing phenomenon associated with electrical leakage at the wheel/rail interface was considered an alternative formation mechanism of WELs observed on rails. A revised rail grinding strategy was proposed by considering the formation of WELs and addressing it thought more regular, relatively shallow grinding to effectively control squat defects.

  • Comprehensive investigation of the microstructure-property relationship of differently manufactured Co–Cr–C alloys at room and elevated temperature
    Wear (IF 2.95) Pub Date : 2019-11-22
    Julian Krell, Arne Röttger, Werner Theisen

    The purpose of this study was to investigate the influence of the microstructure on sliding wear and hardness of four different Co–Cr–C alloys at room and elevated temperature. Different microstructures were produced by applying three different processes. The hardness, hot hardness and wear loss at RT of these alloys correlates strongly with the carbide volume content. In sliding wear tests against an Al2O3 ball, abrasive wear occurs at room temperature. The size or geometric arrangement of the carbides or metal matrix plays a minor role at room temperature. At 600 °C the wear behaviour changes due to the softening matrix. In alloys with small free matrix path lengths, the highest wear rates occur due to micro-fatigue and micro-cracking. In hypoeutectic alloys with a high free matrix path length, the carbides lose their effectiveness due to the lack of support by the matrix. In these alloys, wear is dominated by the properties of the matrix. A hypereutectic casting alloy with large primary carbides shows the best wear results, as the carbides support themselves due to their size and retain their wear-reducing effect.

  • Improvement in the abrasive wear resistance of an aluminum alloy casting for a continuously-variable transmission using heat treatment and pulsed anodizing
    Wear (IF 2.95) Pub Date : 2019-11-21
    Ming-Hung Chiang, Chi-Chen Yeh, Chien-Liang Lee

    The purpose of this work was to investigate whether a modified anodizing process can successfully be applied to an ADC14 aluminum alloy casting to reduce its wear in a continuously-variable transmission component. The oxide film is formed by pulse anodizing after alloy heat treatment. The thickness and hardness of the oxide film were increased by adjusting the heat treatment temperature and by using an electrolyte composed of sulfuric acid, oxalic acid, and aluminum sulphate. The maximum thickness and hardness of the film were 18.3 μm and 442 HV, respectively. The film was produced by heat treating the casting at 350 °C, then pulse-anodizing it for 120 min. The wear loss of the oxide film was minimal under reciprocating, linear abrasion tests which lasted 5000 cycles. To validate the process in a practical application, the oxide film also exhibited good wear resistance when applied in a motorcycle engine that used a continuously-variable transmission. In addition, the engine horsepower was not compromised.

  • Tribological behavior of duplex-coating on Vanadis 10 cold work tool steel
    Wear (IF 2.95) Pub Date : 2019-11-20
    B.F. Zappelino, E.A. dos S. deAlmeida, A.P. Krelling, C.E. da Costa, L.C. Fontana, J.C.G. Milan

    Powder metallurgy Vanadis 10 has an extensive range of applications as dies for extrusion and cold drawing. The tool surface is exposed to different requests (mechanical, chemical and tribological) and demands surface treatments to prolong its life. Few studies investigate the surface modification to optimize the tribological behavior of Vanadis 10. In this study, the combination of cryogenic treatment, two conditions of pulsed plasma nitriding and multilayer TiCN/AlTiN/CrAlTiN/CrN film deposition were evaluated. Pin-on-disc sliding tests were carried out at 0.1 m/s sliding speed, applied load of 10 N and sliding distance of 1000 m. The average hardness of all experimental conditions with multilayer film (2000 HV0.1) was approximately 2 times greater than the hardness of sub-zero treated Vanadis 10 (964 HV0.1). Plasma nitriding promoted the formation of Fe3N-ε compound layer in both experimental conditions. Cracks were observed in this layer. Duplex treatment does not guarantee satisfactory substrate-coating adhesion, because it depends on plasma nitriding conditions. Cryogenic treatment samples followed by plasma nitriding at 5% N2, 75% H2 and 20% Ar, presented higher dry sliding wear resistance in all tested conditions. This treatment is recommended for applications where Vanadis 10 requires high resistance to dry sliding wear.

  • Wheel wear analysis of motor and unpowered car of a high-speed train
    Wear (IF 2.95) Pub Date : 2019-11-19
    Zhiwei Wang, Ruichen Wang, David Crosbee, Paul Allen, Yunguang Ye, Weihua Zhang

    The wheel-wear characteristics of the motor and unpowered car of a high-speed train were investigated, for the first time, by a wheel-wear prediction model comprising a wheel-wear sub-model, an unpowered car dynamics sub-model, and a novel motor-car dynamics sub-model. The motor-car dynamics model considers the detailed structural characteristics and working mechanics of the traction transmission system. Assuming the real track parameters and track irregularities, it handles the nonlinear factors such as the traction characteristics, gear backlash, time-varying mesh stiffness, gear friction and wheel–rail contact. This study assessed the wheel-wear characteristics of a high-speed train by suitable performance indices (wheel-wear depth and contact patch energy). Finally, the model was validated by comparing the simulation results with those of field tests. The predicted and measured wheel wear were in good agreement. Both the wheel wear depth and contact energy were higher for the motor car than the unpowered car, because the traction torque on the wheelsets of the motor car increased the longitudinal creepage. During one re-profiling cycle, the transmission stability of the gear transmission system worsened with continuous wheel-wear. Furthermore, the proposed methods can assess the wheel wear and working status of the traction transmission system in the vehicle vibration environment of any rail vehicle.

  • Effects of carbon content and hardness on rolling contact fatigue resistance in heavily loaded pearlitic rail steels
    Wear (IF 2.95) Pub Date : 2019-11-15
    Masaharu Ueda, Kenji Matsuda

    To reproduce the rolling contact fatigue (RCF) damage of rail steel used in heavy haul railways and to clarify its possible mechanism, the RCF characteristics of pearlitic steel with different carbon content and initial hardness values are evaluated using a two-disk-type machine. The results indicate that the number of spalls and the crack depth decrease with increasing carbon content of pearlitic steel even when the initial hardness is almost the same level. Furthermore, an increase in the carbon content increases the hardness of the rolling contact surface, resulting in the suppression of the plastic flow development. Results also indicate that the crack inclination angle varies depending on the carbon content. According to these results, a possible mechanism for the suppression of fatigue crack propagation in higher carbon pearlitic steel is proposed on the basis of the fracture mechanics approach.

  • Analytical model for predicting false brinelling in bearings
    Wear (IF 2.95) Pub Date : 2019-11-15
    O. Brinji, K. Fallahnezhad, P.A. Meehan

    An analytical model is developed to simulate false brinelling in a bearing based on the theory of energy dissipation. This model is capable of predicting false brinelling damage when the bearings are under vibrating conditions. The bearing used in this simulation is a cylindrical roller bearing which is made of 52100 high carbon bearing quality steel (ASTM A295). The model provides a local prediction of false brinelling for the position of each roller of a cylindrical roller bearing. The model is validated using the modified 3D FE model and test-rig developed by the authors in previous work. The analytical model is shown to be far more time-efficient (by more than 10000 times) compared with the false brinelling 3D FE model. The model is used to compare the false brinelling damage in the inner and outer raceways, in both the lateral and axial directions of the bearing. The results showed that the wear marks on the outer raceway were approximately 5% shallower than the ones on the inner raceway; the volume of wear on the outer raceway was about 9% greater than the wear on the inner raceway. The model is also used to investigate the influence of the amplitude of the normal load and vibration on the wear damage caused by false brinelling. It is shown that the depth of wear increases when the normal load is decreased, and the vibration amplitude is increased. This change is particularly significant when the normal load (maximum contact pressure) on the bearing is less than 1000 N (800 MPa).

  • Dry sliding wear behaviour of thixoformed Al-5.7Si–2Cu-0.3 Mg alloys at high temperatures using Taguchi method
    Wear (IF 2.95) Pub Date : 2019-11-14
    M.A. Abdelgnei, M.Z. Omar, M.J. Ghazali, M.N. Mohammed, B. Rashid

    Present work focused on the impact of high temperature on the tribological properties for thixoformed Al-5.7Si–2Cu-0.3 Mg alloy. A pin-on-disc tribometer was used for dry sliding wear experiments that were executed according to Taguchi method. Wear behaviour was investigated under four process parameters at three levels: process (as-cast, thixoforming, and thixoforming-T6), load (10, 50, and 100 N), sliding temperature (25, 150, and 300 °C), and sliding distance (1000, 3000, and 5000 m). Microstructure was characterized and evaluated by optical microscopy, scanning electron microscopy with energy dispersive X-ray detector, and X-ray diffraction. Results revealed that the thixoformed-T6 alloy consisted of fine globular structure and equiaxed grains, which showed excellent wear resistance at elevated temperature. The experimental values, which were within the permissible limits for the volume loss and coefficient of friction, were congruent to the predicted values because both performed at the rates of 96% and 89%, respectively. Despite increasing wear resistance of the thixoformed-T6 alloy at a sliding temperature of 300 °C, applied load of 100 N, and sliding distance of 3000 m, the best coefficient of friction was attained by the thixoformed-T6 alloy at a sliding temperature of 150 °C, applied load of 100 N, and sliding distance of 5000 m. The dominant wear mechanisms in tribological tests included abrasion, adhesion, and minor delamination.

  • Wear induced ripplocation during dry sliding wear of TiC-based composite
    Wear (IF 2.95) Pub Date : 2019-11-13
    Carl Magnus, Ali Mostaed, William M. Rainforth

    Monolithic TiC and TiC composite containing 30 and 50 mol%SiC were consolidated and synthesized using spark plasma sintering (SPS) without sintering aids. The as-sintered bulk samples microstructural and dry sliding room-temperature tribological properties against Al2O3 were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman analyses. The role of mismatch in coefficient of thermal expansion (CTE) between TiC and SiC as well as cubic to hexagonal SiC phase transformation on the evolution of residual stresses in the composite was also investigated. The friction and wear properties of the monolithic TiC were superior to that of the composite with frictional heating-induced tribo-oxidation playing a dominant role in the wear mechanism. The increase in friction and wear of the composite is attributed to wear-induced stress-relaxation of the previously trapped residual stresses in the composite leading to extensive ripplocation of the TiC grains and consequent SiC grain pull-outs. Herein, we report for the first time on the wear-induced mechanical exfoliation of carbon, its subsequent decomposition into graphite and eventual deformation by micromechanism involving nucleation and propagation of ripples.

  • A hybrid model for wear prediction of a single revolute joint considering a time-varying lubrication condition
    Wear (IF 2.95) Pub Date : 2019-11-11
    Xinchen Zhuang, Sajad Saraygord Afshari, Tianxiang Yu, Xihui Liang

    Wear of revolute joints critically influences the service life and maintenance of certain types of machinery. As a result, many methods have been developed to investigate the wear of revolute joints based on the assumption of either dry contact or full-film lubrication. However, in real applications, a revolute joint may operate under different lubrication conditions during its lifecycle. In this paper, a hybrid model is proposed for wear prediction of a single revolute joint that may experience different lubrication conditions. Three lubrication conditions are considered: full-film lubrication, boundary lubrication, and dry contact. A time-varying wear coefficient is introduced to represent these different lubrication conditions. In our hybrid model, the Archard wear model is used. An adaptive finite element model is used to perform wear simulation of a single revolute joint by continuously updating the contact nodes. In the finite element model, two friction coefficients are used to take into account the change of lubrication conditions. To achieve more accurate predictions and reduce uncertainties of the wear coefficient, the Bayesian updating method is implemented using experimental wear data. The proposed approach is tested using wear experiments of a revolute joint used in an airplane cabin door. The journal material in this experiment is 0.45C steel and the bearing material is brass H58. A comparative study was also conducted between the proposed approach and two other methods. Results show that the proposed approach can more accurately predict the remaining useful life of a single revolute joint.

  • Improvement of tribological properties of sintered self-lubricating composites produced by surface Mo-enrichment
    Wear (IF 2.95) Pub Date : 2019-11-09
    Keli Vanessa Salvador Damin, Gabriel da Rosa Tasior, Alícia Correa Lucena, Tatiana Bendo, Gisele Hammes, Aloisio Nelmo Klein, José Daniel Biasoli de Mello, Cristiano Binder

    In powder metallurgy, a high-cost method that is widely used to increase the useful life of the mechanical components is the addition of alloying elements. A less-exploited process is surface enrichment by plasma, where the same result is obtained only on the surface of the component at a rather lower cost. This paper reports on the improvement of the tribological properties of powder injection molding (PIM) self-lubricating composites produced by surface Mo-enrichment. The tribological properties were evaluated in terms of the scuffing resistance, friction coefficient, and wear rate values of enriched and non-enriched specimens, and counter-bodies. Scanning electron microscopy with energy dispersive X-ray spectroscopy and μRaman spectroscopy were used to characterize the wear scars. The results showed that Mo enrichment increased the scuffing resistance by an impressive 2000%, with a 90% decrease in the wear rate of the specimens and counter-bodies. These results were ascribed to several factors, including the microstructural modification, hardness increase, and tribolayer formation.

  • Improvement in the wear resistance of a hypereutectoid rail via heat treatment
    Wear (IF 2.95) Pub Date : 2019-11-09
    Gustavo Tressia, Amilton Sinatora, Hélio Goldenstein, Mohammad Masoumi

    The rail, as the most important component in railways, needs to be routinely checked to maintain proper service conditions to prevent catastrophic accidents by any premature failure of the rail. The severe plastic deformation of rails due to cyclic wheel/rail contact forces forms a superficial deformed layer, referred to as the white etching layer, because of cementite decomposition and the formation of the carbon-supersaturated nanostructured ferrite phase. This supersaturated superficial layer is highly prone to the initiation and propagation of rolling contact fatigue cracks. However, it has been observed that transition carbides and cementite can precipitate when the first and third stages of tempering starts at approximately 150 and 400 °C, respectively, due to carbon ejection from the body-centered tetragonal structure. A controlled laboratory heat treatment was conducted on a used hypereutectoid rail at 200 and 500 °C. Then, the wear resistances of the heat-treated samples were compared with the as-received rail sample using pin-on-disc testing. A significant increase in the wear resistance of the sample treated at 200 °C confirmed the improvement in the wear resistance of used pearlitic rails, which is a great interest for railway industries.

  • Sliding wear and fatigue cracking damage mechanisms in reciprocal and unidirectional sliding of high-strength steels in dry contact
    Wear (IF 2.95) Pub Date : 2019-11-09
    Abdulbaset Mussa, Pavel Krakhmalev, Jens Bergström

    Rock drill components operate under tough contact conditions during rock drilling. Reciprocal and unidirectional motion under high contact stresses are the common contact conditions between interconnected components. It will result in component damage and often the observed surface damage of rock drill tools is due to wear and fatigue cracks. Nevertheless, the effects of the properties and structure of the mating materials on tribological performance, is not fully understood. The present study is dedicated to simulation and investigation of the wear mechanisms observed in reciprocal and unidirectional sliding of high strength steels for rock drill components. A high strength martensitic steel, 22NiCrMo12–F, commonly used in rock drills was tested in self-mating contact. Wear mechanisms were investigated by means of electron microscopy and wear damage was quantified by a 3D optical interferometer. Total damage, as a result of adhesive wear, severe plastic deformation and nucleation and propagation of fatigue cracks, was discussed in relation to test conditions and material properties. It was observed that the coefficient of friction decreased with increasing normal load. Moreover, the results showed that the type of motion had a significant influence on the worn volume and crack nucleation of the specimens in sliding contact. In addition, the reciprocal motion resulted in higher wear than unidirectional motion under the same test conditions.

  • Effect of temperature on microstructure, properties and sliding wear behavior of low alloy wear-resistant martensitic steel
    Wear (IF 2.95) Pub Date : 2019-11-09
    Chengru Li, Xiangtao Deng, Long Huang, Ye Jia, Zhaodong Wang

    Low alloy wear-resistant martensitic steels are increasingly prevalent in moderate-to-high temperature applications in machinery. In this study, the reciprocating sliding wear behavior of a designed low alloy martensitic steel (herein called HTP) against silicon nitride has been investigated within the temperature range of 300–500 °C and compared to similar results for another wear-resistant steel (NM400). A commercial high temperature friction and wear tester was used. The evolution of the microstructure and properties of HTP and their influence on the wear process was investigated as a function of temperature. Results have shown that as the tempering temperature was increased to 500 °C, the wear depth was significantly reduced. This is attributed to increasing the strength and hardness by 25%. As a result, high temperature wear resistance of the HTP was increased by a factor of 1.7 times relative to alloy NM400. By delaying the decrease of dislocation density and carbide precipitation during the tempering of the martensite, the transformation of microstructure from tempered martensite to tempered sorbite could be hindered, thereby improving the thermal strength of the HTP alloy's matrix. The material removal mechanisms was observed to change from fatigue spalling and abrasive wear to oxidative wear and plastic deformation when the temperature was increased from 300 °C to 500 °C.

  • Performance of wear resistant MCrAlY coatings with oxide dispersion strengthening
    Wear (IF 2.95) Pub Date : 2019-11-08
    Giovanni Bolelli, Christoph Vorkötter, Luca Lusvarghi, Stefania Morelli, Veronica Testa, Robert Vaßen
  • Geometrical aspects of nanofillers influence the tribological performance of Al-based nanocomposites
    Wear (IF 2.95) Pub Date : 2019-11-08
    Soroosh Mohammadi, Abbas Montazeri, Herbert M. Urbassek
  • Tribological analysis of a novel lubricant additive: Pyrone esters
    Wear (IF 2.95) Pub Date : 2019-11-06
    Derek White, Kyle Podolak, George A. Kraus, Sriram Sundararajan

    This work evaluates the friction and anti-wear properties under boundary lubrication of novel lubricity additives derived from 2-pyrone. Pyrone Esters (PEs) of varying carbon chain lengths were synthesized by reacting coumalic acid chloride with alcohols. Chemical composition was verified via NMR and mass spectroscopy while rheological behavior was characterized with a parallel plate rheometer. In comparison, a commercially available monoester was tested. For friction and wear testing, all additives were blended at 1% by weight into a mineral base oil. Neat oil served as the control. A custom reciprocating microtribometer and temperature controlled stage was used to generate wear scars and record the time-evolving friction response. Results showed that the addition of certain PEs reduced friction by up to 25% and mitigated wear by up to 60% in comparison to the neat oil. Subsequently, PE demonstrated its superb potential as an environmentally friendly base stock or lubricant additive.

  • Dry sliding wear behaviour of HVOF thermal sprayed WC-Co-Cr and WC-CrxCy-Ni coatings
    Wear (IF 2.95) Pub Date : 2019-11-06
    Bo Song, James W. Murray, Richard G. Wellman, Zdenek Pala, Tanvir Hussain

    High velocity oxy-fuel (HVOF) thermal spray process shown obvious advantages over other surface hardening techniques when depositing WC-based layers, such as the cladding, electrodeposition, chemical/physical vapour deposition (CVD/PVD) methods, due to its versatility, survivability of hardening phase and low cost. HVOF thermal sprayed WC-based coatings are widely used in components that operates in various environment (temperature, moisture, pressure and etc.) need excellent sliding, fretting, abrasion and erosion resistance. WC-CrxCy-Ni coating shows better wear performance than the WC-Co-Cr coating at high temperature but inferior wear performance at room temperature at lower loads according to literature; however, the wear performance and relevant mechanisms of these two coatings under higher loads has not been reported. To fill this knowledge gap, wear testing of HVOF thermal sprayed WC-CrxCy-Ni and WC-Co-Cr coatings under high loads (96, 240 and 318 N) against a sintered WC-Co (6 mm diameter) ball counter-body was studied in this paper. For WC-CrxCy-Ni coating, decarburization of CrxCy rather than WC, took place during spraying. While the decarburization of WC to W2C occurred in the WC-Co-Cr coating. The major hardening phase – WC, dominates the wear performance of the coatings given its high hardness and small size and Co also appears to be a superior binder phase than Ni. At the maximum load, the specific wear rate of WC-CrxCy-Ni coating when paired with WC-Co counter body was 17.92 × 10-7 mm3 N-1m-1, which is two times of the WC-Co-Cr coating (9.81 × 10-7 mm3 N-1m-1). The wear mechanism for WC-CrxCy-Ni coatings include abrasion of the matrix, cracking of the secondary carbide phase (expected to be brittle) and pulling out of WC particles. For WC-Co-Cr coatings, abrasion of the matrix was marginal, and cracking of the secondary carbide was not observed. The presence of CrxCy of lower hardness than the WC decreases the wear resistance of entire WC-based coating at room temperature, and improves oxidation resistance to the WC at high temperature due to the higher affinity of Cr to O. Hence, the secondary carbide hardening phase may be detrimental when considering the wear resistance application of HVOF thermal sprayed WC-based coatings.

  • Corrosive wear of multi-layer Fe-based coatings laser cladded from amorphous powders
    Wear (IF 2.95) Pub Date : 2019-11-04
    Xiulin Ji, Chanyuan Luo, Yong Sun, Jianhua Zhao
  • Effect of pressure in the transition between moderate and severe wear regimes in brake friction materials
    Wear (IF 2.95) Pub Date : 2019-11-03
    L.Y. Barros, J.C. Poletto, D. Buneder, P.D. Neis, N.F. Ferreira, R.P. Pavlak, L.T. Matozo

    The transition in wear regime is a tribological phenomenon observed in many materials, where a sudden change in wear regime (from moderate to severe) occurs when operating parameters (e.g. pressure or sliding velocity) are changed. However, this phenomenon is rarely explored in brake friction materials (BFMs). Severe wear regime for BFMs results in an increase in cost and leads to environmental issues due to the high amount of loss in material. This work aims to study the transition in BFM applying different levels of pressure, where a BFM was rubbed against a grey cast iron disc in a tribometer. The tribofilm deposited on the disc surface and the area ratio of contact plateaus of BFMs were analyzed. The coefficient of friction (COF) and the BFM's wear were also measured. The wear regime changed from moderate to severe at a limit pressure of 90 bar. At the severe wear regime, a sudden increase in the COF was observed, and the wear of the BFM was approximately 13 times higher than in the moderate wear regime. It was also seen a removal of the tribofilm deposited on the disc's surface and a reduction of contact plateaus over the BFM's surface.

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上海纽约大学William Glover