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  • Correction to: Network-Strengthened Ti-6Al-4V/(TiC+TiB) Composites: Powder Metallurgy Processing and Enhanced Tensile Properties at Elevated Temperatures
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-23
    Shaolou Wei, Lujun Huang, Xinting Li, Yang Jiao, Wei Ren, Lin Geng

    In the original article, there is an error in Figure 1. The unit of Specific strength should be MPa/(g•cm-3). Following is the corrected figure:

    更新日期:2020-02-03
  • Correction to: Advancement in the Pressureless Sintering of CP Titanium Using High-Frequency Induction Heating
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-13
    Stella Raynova, Yan Collas, Fei Yang, Leandro Bolzoni

    The article “Advancement in the Pressureless Sintering of CP Titanium Using High-Frequency Induction Heating”, written by Stella Raynova, Yan Collas, Fei Yang, and Leandro Bolzoni was originally published Online First without Open Access. After publication in volume 50A, issue 10, page 4732 the author decided to opt for Open Choice and to make the article an Open Access publication. Therefore, the copyright of the article has been changed to © The Author(s) 2019 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made

    更新日期:2020-02-03
  • Correction to: Evolution of Substructure of a Non-equiatomic FeMnCrCo High Entropy Alloy Deformed at Ambient Temperature
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-10
    A. K. Chandan, S. Tripathy, M. Ghosh, S. G. Chowdhury

    In the original article, the second and third column headings are transposed in Table II.

    更新日期:2020-02-03
  • Heat Treatment Design to Modify the Martensite Misorientation and Obtain Superior Strength–Toughness Combinations
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-20
    D. M. Field, J. S. Montgomery, K. R. Limmer, K. Cho

    Abstract A heat treatment methodology is described for obtaining ultra-high strength (> 1700 MPa) and increased − 40 °C toughness (> 45 J/cm2) in a steel. Thermodynamic approach to design heat treatments is demonstrated and utilized to produce refinement of the prior austenite grain size leading to superior properties. The cleavage energy was shown to correlate to both prior austenite grain size, according to an inverse root relationship, as well as the density of high-angle martensite lath boundaries.

    更新日期:2020-02-03
  • Ablation Behavior of SiC/ZrB 2 Multilayer Coating Prepared by Plasma Spray Method
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-23
    Shahla Torabi, Zia Valefi, Naser Ehsani

    Abstract In this study, a SiC/ZrB2 multilayer coating with a functional gradient structure was prepared on graphite to increase the ablation resistance. The SiC coating as the inner layer was applied by the reactive melt infiltration method. Then, a ZrB2 outer layer coating was applied by argon gas shrouded plasma spray. The effect of the shielding gas flow rate on the amount of oxides and quality of the ZrB2 coating was studied. To evaluate the ablation resistance of the coatings, the specimens were exposed perpendicular to an oxy-propane flame for 60 second with a temperature of 2473 K and heat flux of 3000 kW/m2. The single-layer SiC coating showed 24.24 pct mass loss. The results indicated that applying the ZrB2 coating significantly improved the ablation resistance and reduced the mass ablation rate. In the plasma spray process, by applying the argon shrouding with a flow rate of 150 L/min, the oxidation of ZrB2 phase decreased from 41.6 to 4.8 pct. In addition, the weight loss and mass ablation rate decreased from 12.79 and 1.857 × 10−3 g/cm2/s to 0.12 pct and 0.0393 × 10−3 g/cm2/s, respectively. The improvement of the ablation resistance of the coating prepared by argon gas shrouded plasma spray could be attributed to the lower amount of oxides and pores in the as-sprayed coating and better cohesion of splats.

    更新日期:2020-02-03
  • Mesoscale Modeling of Dynamic Recrystallization: Multilevel Cellular Automaton Simulation Framework
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-06
    Fei Chen, Huajia Zhu, Haiming Zhang, Zhenshan Cui

    Abstract The main attraction of cellular automaton (CA) method used in computational material science lies on not only the simulation of recrystallization without the complicated differential equations calculation, but also the visualization of nucleation and grain growth during discontinuous recrystallization. In this work, by incorporating the idea of multilevel cellular space into the classical CA simulation framework and formulating cellular state transformation rules and data transfer rules between different levels of cellular space, the multilevel cellular automaton (MCA) model for dynamic recrystallization (DRX) is constructed for the first time. The developed MCA model includes a multilevel recrystallized nucleation (MRN) module and a full-field multilevel grain topological deformation (FMGTD) module. The thermal compression experiments of 316LN stainless steel are carried out, and the developed MCA model is applied to the numerical simulation of DRX for 316LN steel. The accuracy and reliability of this model are verified by comparing simulation results with experimental results. The influences of simulation parameters such as the number of levels N in the FMGTD module and the discrete strain increment on simulation results are discussed. The discrete cellular space area (i.e., grain topology mapping accuracy) in the MCA model increases with N but decreases with the discrete strain increment. The results show that the developed MCA model can not only describe the grain topological deformation in the DRX process more accurately but also more compatible with the physical mechanism of recrystallized nucleation. The calculation accuracy of the MCA model is higher than the existing CA model. Besides, the MCA model can be closer to the real deformation process while ensuring the high grain topology mapping accuracy and solve the problem of the loss of grain boundary area in the existing CA model.

    更新日期:2020-02-03
  • 3D Visualization of Top Surface Structure and Pores of 3D Printed Ti-6Al-4V Samples Manufactured with TiC Heterogeneous Nucleation Site Particles
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-23
    Yoshimi Watanabe, Masafumi Sato, Tadachika Chiba, Hisashi Sato, Naoko Sato, Shizuka Nakano

    Abstract In this study, the effects of TiC heterogeneous nucleation site particles on the formability and microstructure of additive manufactured (AMed) Ti-6Al-4V samples fabricated by selective laser melting are investigated. Laser confocal microscopy and X-ray computer tomography techniques have been applied to AMed samples for visualization of the top surface and pore structures in 3D. The density of AMed Ti-6Al-4V samples was found to be increased by the addition of TiC particles. It could be concluded that the addition of heterogeneous nucleation site particles is one of the key technologies to achieve higher formability, improved microstructure, and enhanced mechanical properties for AMed products.

    更新日期:2020-02-03
  • Unravelling Microstructure Evolution and Grain Boundary Misorientation in Coarse-Grained Heat-Affected Zone of EH420 Shipbuilding Steel Subject to Varied Welding Heat Inputs
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-10
    Xiaodong Zou, Jincheng Sun, Hiroyuki Matsuura, Cong Wang

    Abstract Microstructure evolution and grain boundary misorientation in coarse-grained heat-affected zone of EH420 shipbuilding steel have been investigated at different welding heat inputs. As heat input increases, main constituents transform from lath bainites to granular bainites, and to acicular ferrites as a result of reduced cooling rate. Corresponding fraction of high angle grain boundaries decreases from 28.24 to 20.04 pct as heat input is raised from 50 to 150 kJ/cm but reverses to 29.04 pct at 200 kJ/cm.

    更新日期:2020-02-03
  • Creep Deformation Behavior of a Novel Precipitate-Hardened Ni-Fe-Base Superalloy at 750 °C
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-06
    P. Zhang, Y. Yuan, Y. F. Gu, Y. Y. Dang, J. B. Yan, J. T. Lu, J. C. Wang

    Abstract The creep deformation behavior of a novel precipitate-hardened Ni-Fe-base superalloy in solutionized and aged states is investigated at 750 °C/80 to 120 MPa. We found that as creep deformation proceeds, creep curves of specimens in the two states either overlap or are parallel to each other. This study provides a new strategy to design the heat treatment scheme to achieve a good compromise between the strength and fabricability of superalloys for 700 °C-class advanced ultra-supercritical power plants.

    更新日期:2020-02-03
  • Nanostructured NiTi Shape Memory Alloy Via Ni/Ti Nanolamination
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-07
    Jintao Zhang, Hua Ding, Minghui Cai, Ning Zhang, Haitao Qu, Shuxia Li, Hongliang Hou, Peng Cao

    Abstract Ultrafine grained NiTi shape memory alloy was consolidated from Ni/Ti laminates via accumulative roll bonding (ARB) followed by hot isostatic pressing (HIP). Due to the extensive plastic deformation arising from ARB and the attainment of ultra-thin layers of both Ti and Ni laminates, the subsequent HIP processing time was significantly reduced. Differential scanning calorimetry (DSC) analysis confirms that the shape memory effect was obtained in the consolidated NiTi alloy.

    更新日期:2020-02-03
  • Recrystallization and Grain Growth Simulations for Multiple-Pass Rolling and Annealing of U-10Mo
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
    William Frazier, Chao Wang, Zhijie Xu, Nicole Overman, Shenyang Hu, Vineet V. Joshi

    Abstract A simulation model of recrystallization and grain growth has been developed to investigate grain structure evolution during deformation and heat treatment in polycrystalline U-10 wt pct Mo (U-10Mo) fuel. Experimentally obtained U-10Mo post-homogenization microstructures were used as input for closed-loop simulations of multiple rolling passes, intermediate heating, and final annealing. Finite element model calculations of deformation and Potts model simulations of recrystallization and grain growth were used to iteratively inform each subsequent stage of simulation. The model was then applied to predict the grain structure evolution during multiple-pass hot rolling and annealing of U-10Mo and benchmarked against experimentally observed U-10Mo recrystallization behavior. The results showed that our model was able to capture the coupling between deformation and recrystallization as a function of microstructure, including particle stimulated nucleation and recrystallization nucleation on grain boundaries. Additionally, we have achieved reasonable quantitative agreement with U-10Mo recrystallization and grain growth behavior.

    更新日期:2020-01-31
  • Microstructural Investigation of the Impact Weld Interface of Pseudo Single Grained Cu and Ag
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-26
    Taeseon Lee, Menglin Zhu, Taylor Dittrich, Jinwoo Hwang, Anupam Vivek, Glenn S. Daehn

    The microstructure of the impact weld interface of pseudo single grained copper and silver is investigated. Electron backscattered diffraction shows severe plastic deformation at the weld interface and suggests that the cooling rate of the interface is fast enough to avoid conventional eutectic lamellar structure in localized melted zones. Scanning transmission electron microscopy, along with nano-diffraction and compositional analysis, demonstrates that impact welding can achieve metallurgical bonding in the solid-state without forming an amorphous structure.

    更新日期:2020-01-06
  • Correlation Between Microstructural Architecture and Mechanical Behavior of Single-Walled Carbon Nanotube-Aluminum Composites
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-27
    Yan Shi, Yang Lu, Zihong Ni, Lei Zhao, Zhiqiang Li, Ding-Bang Xiong, Jin Zou, Qiang Guo

    Abstract Single-walled carbon nanotube (SWCNT)-aluminum (Al) composites with three distinct microstructural architectures (nanolaminated structure with relatively weak interfacial bonding, partial laminated structure with strong interfacial bonding, and disordered microstructure) were fabricated. Tensile test revealed that partial laminated composite possessed the highest yield and tensile strengths with an almost identical uniform elongation among the three composites, which were rationalized by grain refinement of Al matrix, effective load-sharing of SWCNTs, and enhanced interface-dislocation interactions in partial laminated composite.

    更新日期:2020-01-06
  • Study of Residual Stresses in Additively Manufactured Ti-6Al-4V by Neutron Diffraction Measurements
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-11
    David Gloaguen, Baptiste Girault, Bruno Courant, Pierre-Antoine Dubos, Marie-José Moya, François Edy, Joana Rebelo Kornmeier

    Abstract Neutron diffraction is a powerful non-destructive volumetric evaluation method for the analysis of the internal stress state in components processed by laser powder bed fusion (LPBF). High cooling rates and heterogeneous distribution of temperature during additive manufacturing lead to large residual stress fields. Residual stresses developed during the building process have unquestionably an important influence on the mechanical performance and potentially lead to delamination from the support structures, shape distortion but also crack formation. In the present work, neutron measurements have been carried out on cube-shaped samples prepared by LPBF from a Ti-6Al-4V powder bed. A series of miscellaneous positions (center, edge, and corner) over three different depths (close substrate, middle, and close surface) have been analyzed by neutron diffraction so as to systematically characterize the full stress tensor. The influence of shear stresses and second-order residual stresses on the stress tensor analysis is also discussed in this work.

    更新日期:2020-01-06
  • Testing Model Structure Through a Unification of Some Modern Parametric Models of Creep: An Application to 316H Stainless Steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-11
    M. Evans

    Abstract It is important to be able to predict the creep life of materials used in power plants and in aeroengines. This paper develops a new parametric creep model that extends those put forward by Wilshire and Yang et al. by having them as restricted or special cases of a new generalized model. When this generalized model was applied to failure time data on 316H stainless steel it was found that neither of these established parametric models explained the greatest variation in the experimentally obtained times to failure. Instead, a version of this generalized model was most compatible with the experimental data. It was further found that the activation energy for this material changed at a normalized stress of 0.41 due to a change from the domination of dislocation movement within grains to movement within grain boundaries. Finally, when the generalized model was used to predict failure times beyond 5000 hours (using only the shorter test times), the new generalized model had better predictive capability at most temperatures.

    更新日期:2020-01-06
  • Processing and Characterization of Extremely Hard and Strong Cu-(0-15 wt pct)Al Alloys
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-26
    Mahammad Ali Shaik, Brahma Raju Golla, Suresh Babu Pitchuka

    The present work investigates the microstructure development and mechanical properties of mechanically alloyed and hot-pressed copper (Cu)-X wt pct aluminum (Al) (X = 0, 3, 5, 10, 15) alloys. The morphology of the ball-milled Cu-Al powders changed from coarse flaky structure to small hard agglomerates with the addition of Al. It was observed that the density of Cu-Al samples varied between ~ 95 and 98 pct of theoretical density (ρth) after hot pressing (Temperature: 500 °C, Pressure: 500 MPa, Time: 30 min). The crystallite size of Cu-Al samples decreased for both the milled powders and hot-pressed samples. The XRD and SEM-EDS analyses of the hot-pressed samples confirmed the presence of α-Cu solid solution phases for the Cu alloyed with Al up to 5 wt pct. On the other hand, further addition of Al to Cu leads to the formation of both intermetallic compound (Cu9Al4) and solid solution phase. The nano-indentation tests indicated a significant increase in hardness (2.4 to 7.9 GPa) and elastic modulus (121.1 to 177.4 GPa) of Cu-Al alloys. The Cu-Al alloys were measured with very high compressive strength (813.8 to 1120.2 MPa) and the compressive strain varied in the range of 29.81 to 5.81 pct.

    更新日期:2020-01-06
  • A Data-Driven Scheme for Quantitative Analysis of Texture
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-01
    Yafei Wang, Chenfan Yu, Leilei Xing, Kailun Li, Jinhan Chen, Wei Liu, Jing Ma, Zhijian Shen

    Texture is the orientation distribution of crystallites in polycrystalline materials. Given the discrete orientations, Schaeben suggested to adopt statistics for quantitative analysis of texture from discrete orientations, and he also conceived a clustering algorithm to facilitate the applications of statistical methods (H. Schaeben, J Appl Crystal 26:112–121, 1993). This data-driven scheme becomes more urgent and more necessary for the oncoming fourth paradigm: data-intensive scientific discovery, which follows after experimental science, theoretical science, and computational science paradigm. This research adopts a density-based clustering algorithm, DBSCAN, to process the orientation data from an austenitic stainless steel 316 L sample fabricated by selective laser melting. It is validated that the algorithm can robustly identify the orientation cluster (or texture component or preferred orientation). The statistical methods can successfully quantify the features of the identified orientation cluster with quantified uncertainty (statistical significance), which is often lacked in the general method of orientation distribution function. It is believed that this data-driven scheme can be applied to the many aspects of texture analysis.

    更新日期:2020-01-06
  • First-Principles Investigation of Thermodynamic Decomposition of Interfacial Oxides in Hot Compression Bonding
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-11
    Honglin Zhang, Xing-Qiu Chen, Bin Xu, Mingyue Sun, Dianzhong Li

    The removal of interfacial oxides is essential in solid-state bonding to obtain high-performance joints. A recent work reported that the dissolution of MnCr2O4 at the hot compression bonding (HCB) interface of 316LN stainless steel improved the mechanical properties of joints. The evolution behaviors of interfacial oxides behind it should be further understood. In this study, the thermodynamic stability of MnCr2O4 and decomposition mechanisms of interfacial oxides in HCB was studied by combining the first-principles calculations with thermodynamics approach. The results obtained within GGA + U method were compared with experiments and in a good agreement with previous calculated results. The predicted stability region of MnCr2O4 was built by drawing the Mn-Cr-O phase diagram. The transition of its possibly coexisting binary oxides was understood in detail with respect to the environmental conditions. The interfacial oxides evolution in HCB process was proposed based on the variation of oxygen chemical potential. It predicted that MnCr2O4 forms during the heating period of HCB with the presence of binary oxides of Mn and Cr. All possible interfacial oxides decompose into metal phases and oxygen atoms when \( \Delta \mu_{\text{O}} \) is below − 386.97 kJ/mol.

    更新日期:2020-01-06
  • A Novel Rolling Approach to Refining the Microstructure and Enhancing the Mechanical Strength of Pure Aluminium
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-22
    Marta Orłowska, Krzysztof Topolski, Małgorzata Lewandowska

    Abstract In the present study, a novel rolling method is proposed, which is called Multi-Rotational Flat Rolling (MRFR). The novelty of this work is the application of this special method of flat rolling to severely deform metal. The rolling is performed so as to preserve the square shape of the transverse section of the sample. During the process, the transverse-sectional area of the workpiece is gradually reduced, while the sample length is simultaneously increased. The experiment was carried out on commercially pure aluminium. An annealed sample was subjected MRFR up to the attainment of a maximum fourfold reduction in the transverse-sectional area. A microstructure analysis showed that the process resulted in a material having a refined microstructure of less than 1 µm. Nevertheless, the majority of the grain boundaries (over 70 pct) were of the low-angle type. As a result of the grain refinement and the increase in dislocation density, a clear improvement in the strength of the deformed material was observed. The increase in yield stress was 157 pct, the increase in ultimate tensile strength was about 56 pct, while the decrease in the value of elongation to failure was 12.8 pct.

    更新日期:2020-01-06
  • Exploring Correlations Between Properties Using Artificial Neural Networks
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-10-30
    Yiming Zhang, Julian R. G. Evans, Shoufeng Yang

    Abstract The traditional aim of materials science is to establish the causal relationships between composition, processing, structure, and properties with the intention that, eventually, these relationships will make it possible to design materials to meet specifications. This paper explores another approach. If properties are related to structure at different scales, there may be relationships between properties that can be discerned and used to make predictions so that knowledge of some properties in a compositional field can be used to predict others. We use the physical properties of the elements as a dataset because it is expected to be both extensive and reliable and we explore this method by showing how it can be applied to predict the polarizability of the elements from other properties.

    更新日期:2020-01-06
  • Combined Effects of High Undercooling and Large Cooling Rate on the Microstructure Evolution and Hardening Mechanism of Rapidly Solidified Ti-Al Alloys
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-03
    Z. C. Luo, H. P. Wang

    Abstract Controlling the microstructure evolution of Ti-(47, 50, 54) at. pct Al alloys by combining the effects of high undercooling and large cooling rate has been investigated. The calculated undercooling and cooling rates of the three component alloy droplets increase as power functions with the decreasing alloy droplet diameter D. With decreasing D, the microstructure of Ti-47 at. pct Al alloy evolves from dendritic dendrites to equiaxed dendrites, and the main microstructure of Ti-50 at. pct Al alloy transforms from a lamellar microstructure to a non-lamellar microstructure, while that of Ti-54 at. pct Al alloy appears as an interweaving microstructure. The α2 phase with a superlattice structure and the α2n phase with a nonsuperlattice structure are confirmed by transmission electron microscopy, and the large difference of Al contents leads to formation of the α2 phase and the α2n phase. Atomic images show that the interface of the α2n phase and γ phase is coherent. The α2n phase precipitates from the γ phase during cooling. The combined effects of high undercooling and large cooling rate suppress the transformation of the α phase to (α2 + γ) phases. The Young’s modulus first increases and then decreases with decreasing D, while the nanohardness is controlled by the combined factors of the microstructure morphology, phase composition, phase ratio, and grain refinement. As for the microhardness, grain refinement dominates the hardening of the Ti-54 at. pct Al alloys, while the combined factors dominate the hardening of Ti-(47, 50) at. pct Al alloys.

    更新日期:2020-01-04
  • Temperature Dependence of Elastic–Plastic Properties of Fine-Pitch SAC 0307 Solder Joint Using Nanoindentation Approach
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-03
    Azman Jalar, Maria Abu Bakar, Roslina Ismail

    Abstract This paper highlights the advantages of using the nanoindentation approach over the conventional method for the mechanical characterization of components used in electronic packaging. The limitation of the conventional method has become more critical with the miniaturization of electronic packages, giving inadequate information regarding the mechanical properties of metallurgical interconnections. The load–displacement approach via nanoindentation was used in this study to determine the micromechanical properties of a fine-pitch solder joint subjected to aging for 1000 hours. This approach is more advantageous than tensile testing, as it focuses on the elastic behavior unlike that in conventional mechanical testing. The nanoindentation analysis results showed that the elastic–plastic behavior before failure can be assessed in a wide range of temperatures and thus help study the temperature dependence on the mechanical properties of fine-pitch solder joints. The characterization was done beyond the elastic range beforehand of conventional method. The modulus and hardness of the fine-pitch SAC 0307 solder joint decreased while its plastic and elastic behaviors became pronounced at higher aging temperatures. This implies that solder joints become weaker and less resilient with increasing temperature, at least for a duration of 1000 hours.

    更新日期:2020-01-04
  • Excess Solute Carbon and Tetragonality in As-Quenched Fe-1Mn-C (C:0.07 to 0.8 Mass Pct) Martensite
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-03
    Naoki Maruyama, Shinichiro Tabata, Hiroyuki Kawata

    The carbon distribution behavior and crystal structure of as-quenched martensite in Fe-1Mn-C (C: 0.07 to 0.8 mass pct) steels were quantitatively investigated by atom probe tomography (APT) and X-ray diffraction with Rietveld analysis. APT revealed that the martensite steels contained quantities of carbon in solid solution far beyond its solubility in body-centered cubic (bcc)-Fe in all the alloys investigated; the carbon atoms were non-homogeneously distributed as carbides or aggregates on dislocations due to autotempering. Tetragonality was observed in the steels with interstitial solute carbon concentrations in the range of 0.1 to 0.7 mass pct, but was not evident below 0.1 mass pct. The appearance and disappearance of tetragonality in the low-carbon steels may be explained by the disordered bcc ↔ ordered body-centered tetragonal (bct) mechanism, considering the partial tetragonality due to the heterogeneity of the interstitial solute carbon distribution. The existence of tetragonality in the autotempered low-carbon steels can alternatively be understood by a mechanism based on the kinetic decrease of tetragonality during cooling, where the microscopic strain release is the rate-controlling process. The excess carbon solubility in the autotempered low- and medium-carbon martensite is due to the existence of tetragonal distortions, owing to the slow kinetics of the tetragonality decrease during cooling.

    更新日期:2020-01-04
  • Numerical Prediction and Experimental Validation of the Microstructure of Bearing Steel Ball Formation in Warm Skew Rolling
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-03
    Yuanming Huo, Tao He, Baoyu Wang, Zhenhua Zheng, Yong Xue

    Direct deformation spheroidization (DDS) of carbides in warm conditions can improve the microstructure and performance of bearing steel. In this study, based on the carbide spheroidization mechanism, a set of multiaxial constitutive equations was developed to predict the microstructure evolution of bearing steel 52100 during warm skew rolling (SR). The derived multiaxial constitutive equations were implemented in DEFORM-3D software through a user subroutine. FE simulation of warm SR was performed to predict the formation and microstructure evolution of bearing steel balls (BSBs). The distribution of the normalized dislocation density, carbide phase transformation fraction and carbide spheroidization fraction within BSBs was predicted via FE simulation of warm SR. To validate the FE simulation results, warm SR experiments were conducted to produce BSB specimens with 30 mm diameter. The microstructure of BSB specimens was observed to analyze their microstructure distribution in the longitudinal and transversal sections. The predicted and experimental results were compared, and the results show that the predicted carbide spheroidization distribution agrees well with the experimental results. This indicates that the formation and microstructure of BSB during warm SR can be predicted well using the derived multiaxial constitutive equations.

    更新日期:2020-01-04
  • Devitrification of Mechanically Alloyed Fe-Nb System: Mössbauer Study of the Intermetallic Phases
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-03
    A. F. Manchón-Gordón, P. Svec, J. J. Ipus, M. Kowalczyk, J. S. Blázquez, C. F. Conde, A. Conde, P. Svec, T. Kulik

    Abstract Intermetallic phases in the Fe-Nb system have been obtained as products of the devitrification of a homogeneous amorphous Fe70Nb30 alloy prepared by mechanical alloying. Besides Fe2Nb Laves and Fe7Nb6 intermetallic phases, α-Fe phase has been detected by X-ray diffraction (XRD). Hyperfine parameters for both Fe2Nb and Fe7Nb6 intermetallics have been obtained from Mössbauer spectroscopy in correlation with phase identification from XRD results. Thermomagnetic measurements show changes in the Curie temperatures of the amorphous and Fe2Nb phases during the crystallization, due to compositional variations related to the developing of the α-Fe phase. Kinetics of the crystallization process has been analyzed using the classical Johnson-Mehl-Avrami-Kolmogorov kinetic theory in both isothermal and non-isothermal regimes.

    更新日期:2020-01-04
  • Solidification Characteristics and Segregation Behavior of Cu-15Ni-8Sn Alloy
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-02
    Zhongkai Guo, Jinchuan Jie, Shichao Liu, Jiaming Liu, Shipeng Yue, Yubo Zhang, Tingju Li

    The solidification characteristics and segregation behavior of Cu-15Ni-8Sn alloy were systematically investigated in the present study. The solidification characteristics were revealed with the assistance of a solidification quenching experiment, DTA analysis and Scheil simulation. The solidification microstructure of Cu-15Ni-8Sn alloy was characterized by SEM, and the results indicated that the as-cast microstructure of Cu-15Ni-8Sn alloy mainly consists of Sn-depleted α-Cu(Ni,Sn) matrix, Sn-rich γ phase and lamellar (α + γ) structure. It has been demonstrated that the solidification process begins with the nucleation and growth of primary Sn-depleted α1 phase (\( L \to \alpha_{1} \) at 1114 °C) and terminates with the divorced eutectic reaction (\( L_{2} \to \alpha_{2} + \gamma \) at 868 °C). During the subsequent cooling process, the discontinuous precipitation (\( \alpha_{2} \to \alpha_{1} + \gamma \)) takes place in the temperature range from about 700 °C to 600 °C. In addition, the macrosegregation behavior of Sn in Cu-15Ni-8Sn alloy was investigated by adopting vertical unidirectional solidification and measuring the cooling curves at different positions. The results indicated that an inverse macrosegregation of Sn solute exists in the as-prepared ingot, which mainly segregates at the chill surface of the alloy ingot. Namely, the Sn content is higher than 8 wt pct at the chill surface and about 8 wt pct inside the ingot for Cu-15Ni-8Sn alloy.

    更新日期:2020-01-04
  • Influence of Pore Size and Crystallography on the Small Crack HCF Behavior of an A357-T6 Cast Aluminum Alloy
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-02
    I. Serrano-Munoz, S. Dancette, C. Verdu, J.-Y. Buffiere

    The high-cycle fatigue, small crack propagation behavior of an A357-T6 cast aluminum alloy is investigated. Laboratory X-ray micro-computed tomography \((\mu {\text {CT}})\) is used to assist in the manufacturing of two flat fatigue specimens containing subsurface shrinkage pores of different sizes (Pore 1 \(\sqrt{A} = 522\,\mu {\text {m}}\) against Pore 2 \(\sqrt{A} = 280\,\mu {\text {m}}\)). Surface crack monitoring is performed by means of optical microscopy and the cracked specimens are analyzed via scanning electron microscopy and electron backscatter diffraction techniques. The subsurface pores tend to induce intergranular crack nucleation, principally when the grain boundaries are oriented perpendicular to the loading direction. Pore 1 induces a fatigue life reduction of 500.000 cycles when compared to Pore 2. The crystallography is able to influence small crack propagation by slightly decelerating the crack growth rates as well as by altering the crack path topography. Tailoring of the crystallography for improved fatigue resistance requires an investigation of the optimal largest defect to grain size ratio.

    更新日期:2020-01-04
  • The Effect of Powder Characteristics on Build Quality of High-Purity Tungsten Produced via Laser Powder Bed Fusion (LPBF)
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2020-01-01
    A. C. Field, L. N. Carter, N. J. E. Adkins, M. M. Attallah, M. J. Gorley, M. Strangwood

    Abstract Two high-purity tungsten powders, produced via different manufacturing techniques, were characterized to determine size distribution, morphology, thermal properties, and flow characteristics and, thus, the likely suitability for Laser Powder Bed Fusion (LPBF) production. Specimens from duplicate builds were produced with the two powders and characterized for density, defect mechanisms, and thermal penetration into the substrate plate to compare apparent power densities. The first powder was a chemically reduced powder with irregular morphology and the second, a plasma spheroidized powder with highly spherical morphology. The latter was found to have tighter morphological control and size distribution, having a third of particles at the modal particle size in comparison to a fifth of the chemically reduced powder. This led to better flow characteristics, and an increase of 1.5 g cm−3 (1500 kg m−3) in the packing densities seen in the powder bed which corresponds to 57 pct theoretical density vs 50 pct theoretical density in the chemically reduced powder. As a result, the specimens produced from the plasma spheroidized powder had higher densities (97.3 vs 88.5 pct) and the dominant defect mechanism moved from lack of fusion dominated in the chemically reduced powder to cracking dominated in the plasma spheroidized. The plasma spheroidized powder also showed higher apparent power densities (effective absorptivities) as evidenced by an 80 pct deeper penetration of the laser into the substrate plate.

    更新日期:2020-01-01
  • Atomistic simulations of grain boundary migration in copper
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2006
    Bernd Schönfelder,G√ºnter Gottstein,Lasar S. Shvindlerman

    While the motion of twist boundaries can be readily studied by atomistic simulations with molecular dynamics (MD) under the action of an elastic driving force, the approach fails for tilt boundaries. This is due to the interaction of the elastic stress with the grain boundary (GB) structure, which causes plastic strain by GB sliding. A novel concept, the orientation correlated driving force, is introduced to circumvent this problem. It is shown that this concept can be successfully applied to the study of the migration of tilt boundaries. The migration behavior of several twist and tilt GBs was investigated. The transition from low-to high-angle boundaries can be captured, and a structural transition of tilt boundaries was found at high temperatures, which also affected the migration behavior. The results compare well with experimental results of the motion high-angle boundaries, but for low-angle boundaries, the agreement is poor.

    更新日期:2020-01-01
  • Microstructural Evolution of INCONEL® Alloy 740H® Fusion Welds During Creep
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    Daniel Henry Bechetti,John N. Dupont,John J. de Barbadillo,Brian Andrew Baker,Masashi Watanabe

    Electron microscopy techniques have been used to investigate the cause of premature creep failure in the fusion zone of INCONEL® Alloy 740H® (INCONEL and 740H are registered trademarks of Special Metals Corporation) welds. The reduced creep rupture lives of all-weld-metal and cross-weld creep specimens (relative to base metal specimens) have been attributed to the presence of large grain boundary regions that were denuded in fine γ′ but contained coarse, elongated particles. Investigation of creep rupture specimens has revealed four factors that influence the formation of these coarsened zones, and the large particles found within them have been identified as γ′. Comparisons of the microstructural characteristics of these zones to the characteristics that are typical of denuded zones formed by a variety of mechanisms identified in the literature have been made. It is concluded that the mechanism of γ′-denuded zone formation in alloy 740H is discontinuous coarsening of the γ′ phase. The discontinuous reaction is catalyzed by the grain boundary migration and sliding which occur during creep and likely promoted by the inhomogeneous weld metal microstructure that results from solute segregation during solidification. The increased susceptibility to the formation of the observed γ′-denuded zones in the weld metal as compared to the base metal is discussed in the context of differences in the contributions to the driving force for the discontinuous coarsening reaction.

    更新日期:2020-01-01
  • Cooling Slope Casting Process for Synthesis of Bulk Metallic Glass Based Composites with Semisolid Structure
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2010
    Advenit Makaya,Takuya Tamura,Kenji Miwa

    A process combining cooling slope casting and suction casting was developed to generate a semisolid structure in a Zr-based bulk metallic glass matrix composite. The melt was injected onto a cooling slope and subsequently vacuum sucked into a cylindrical copper mold placed at the end of the slope. The structure obtained for 4-mm-diameter specimens of composition Zr66.4Nb6.4Cu10.5Ni8.7Al8 consists of a dispersion of spheroidal and rosettelike bcc crystals in a glassy matrix. Various slope angles, slope lengths, and injection pressures were tested. The coarsest and most spheroidal crystal structure was obtained at short slope lengths and high injection pressures. Microstructure analysis suggests that the slope is the location of extensive crystal nucleation and possible fragmentation, while the microstructure’s morphological evolution seems to occur mainly in the mold. The semisolid structure is expected to confer improved mechanical properties and ductility to the composite material.

    更新日期:2020-01-01
  • Systematic Phase-Field Study on Microstructure Formation During Brazing of Mar-M247 with a Si-Based AMS4782 Filler
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019
    Bernd Böttger,Matthias Apel,B. Daniels,Lukas Dankl,Thomas Göhler,Theresa Jokisch

    Although advanced solidification processes like high temperature brazing have gained more and more industrial importance, they still are often not well understood, and defining optimal process conditions for practical use in many cases can be achieved only by expensive experimental trial and error methods. On the other hand, the phase-field method has become more and more powerful for the simulation of solidification and phase transformations in technical alloys. This paper presents phase-field simulations for high temperature brazing of the Ni-base superalloy Mar-M247 using a Si-based AMS4782 filler. The applied phase-field model can be online-coupled to Calphad databases which deliver the thermodynamic and mobility data for this complex multicomponent multiphase alloy. Unknown or uncertain physical parameters like diffusion coefficients have been calibrated by comparing to optical micrographs and EDX element mappings obtained from laboratory braze experiments for the same material combination. By variation of the process conditions the effects of the brazing temperature, the brazing time, and the thickness of the braze gap on precipitation of brittle phases and formation of stray grains as well as changes in the microstructure of the base material itself have been systematically investigated. Results are presented and discussed.

    更新日期:2020-01-01
  • Microstructural evolution and superplastic deformation behavior of fine grain 5083Al
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1996
    Peter A Friedman,Amit Kumar Ghosh

    The microstructural evolution during superplastic deformation of a fine grain Al-4.7 pct Mg alloy (5083Al) has been studied quantitatively. Starting from an average grain size of 7 µm, grain growth was monitored in this alloy both under static annealing and with concurrent superplastic deformation at a high test temperature of 550°C. Grain size was averaged from measurements taken in longitudinal, transverse, and thickness directions and was found to grow faster during concurrent superplastic deformation than for static annealing. A grain growth law based on an additive nature between time-based and strain-based growth behavior was used to quantify the dynamics of concurrent grain growth. The extent of void formation during deformation was quantified as the area fraction of voids on L-S planes. This void fraction, referred to as the cavity area percent, was recorded at several levels of strain for specimens deformed at two different strain rates. A constitutive equation incorporating this grain growth data into the stress-strain rate data, determined during the early part of deformation, was generated and utilized to model the superplastic tensile behavior. This model was used in an effort to predict the stress-strain curves in uniaxial tension under constant and variable strain rate conditions. Particular attention was paid to the effects of a rapid prestrain rate on the overall superplastic response and hardening characteristics of this alloy.

    更新日期:2020-01-01
  • An Assessment of Milling Time on the Structure and Properties of a Nanostructured Ferritic Alloy (NFA)
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    Richard DiDomizio,Shenyan Huang,Laura Cerully Dial,Jan Ilavsky,Michael Larsen

    The tensile properties of a 14 wt pct chromium nanostructured ferritic alloy (NFA) are assessed as a function of attrition time. Small angle X-ray scattering results show quantitatively that the number density of precipitated oxides increases as a function of milling time. This difference in oxide density alone is not enough to describe the tensile behavior of the NFA as a function of temperature. As a result, a previously proposed root mean square strengthening model is applied to the current study where direct dispersion strengthening, grain boundary strengthening, dislocation forest hardening, and matrix hardening are all considered. When an optimization routine is conducted, the fitting results suggest that the precipitated oxides are soft obstacles to dislocation motion.

    更新日期:2020-01-01
  • Microstructural Characterization and Mechanical Properties Analysis of Weld Metals with Two Ni Contents During Post-Weld Heat Treatments
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2015
    Da-yong Wu,Xiu-lin Han,Hong-tao Tian,Bo Liao,Fu-ren Xiao

    This study designed post-weld heat treatments, including reheating and tempering, associated with hot bending to investigate the microstructures, toughness, and hardness of two weld metals with different Ni contents (<1 wt pct level). The results indicated that a high Ni content decreased the ferrite transformation temperature and increased the proportion of acicular ferrite (AF). Furthermore, a high Ni content promoted the martensite/austenite (M/A) constituent formation after reheating. The promotion of the M/A formation increased the number of cementite particles, and accelerated cementite coarsening during tempering. The large-angle grain boundary density from the AF improved the toughness despite the negative effect of cementite. The strengthening contributions were calculated, and the grain refinement was the greatest. The high Ni content decreased the effective grain size with a 2 deg tolerance angle, thus enhancing the grain refinement contribution.

    更新日期:2020-01-01
  • On the Modeling of the Diffraction Pattern from Metal Nanocrystals
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    Luca Gelisio,Paolo Scardi

    The powder diffraction patterns of spherical nanocrystals made of five different fcc metals were generated using atomistic models within a Molecular Dynamics simulation. Static and dynamic effects are interpreted and discussed within the framework of two different approaches, respectively, based on (1) a Reciprocal Space and (2) a Direct Space representation of diffraction. Chosen elements display a wide range of properties, especially related to material stiffness and elastic anisotropy, so to deeply challenge interpretation paradigms. The effect of the shape on static and dynamic features is also addressed.

    更新日期:2020-01-01
  • δ/γ Interface bondary sliding as a mechanism for strain accommodation during hot deformation in a duplex stainless steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2000
    A. Piñol-Juez,Amaia Iza-Mendia,Isabel. Gutiérrez

    AbstractIn the present work, the mechanical properties and the microstructural evolution of a duplex stainless steel in the as-cast and wrought conditions during deformation under hot-working conditions have been studied. Hot torsion tests, at strain rates of $$\dot \varepsilon $$ = 1 s−1, have been carried out using prepolished samples on which surface parallel scratches have been practiced. The observation of the surface of the samples shows a large displacement of the scratches produced by two different mechanisms, sliding on the δ/γ interface, and shearing of the ferrite. The displacements in the as-cast condition have been found to concentrate in a reduced set of ferrite/austenite interfaces leading to the formation of cracks along them. In the wrought material, the distribution of the sliding is more homogeneous over all the ferrite/austenite interfaces, and no damage has been produced. These behavioral differences between both materials have been related in the present work, to the characteristics of the corresponding microstructures, to the spatial phase distribution, and to the nature of the ferrite/austenite interface, among others.

    更新日期:2020-01-01
  • The mechanism of brittle fracture in a microalloyed steel: Part I. Inclusion-induced cleavage
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2000
    Douglas P. Fairchild,D. G. Howden,William A. T. Clark

    The cleavage resistance of two microalloyed steels (steels A and B) was studied using several tests, including the instrumented precracked Charpy and Charpy V-notch (CVN) techniques. Ductile-to-brittle transition temperatures were measured for the base-metal and simulated heat-affected zone (HAZ) microstructures. Steel B showed inferior cleavage resistance to steel A, and this could not be explained by differences in gross microstructure. Scanning electron fractography revealed that TiN inclusions were responsible for cleavage initiation in steel B. These inclusions were well bonded to the ferritic matrix. It is believed that a strong inclusion-matrix bond is a key factor in why TiN inclusions are potent cleavage initiators in steel. Strong bonding allows high stresses in a crack/notch-tip plastic zone to act on the inclusions without debonding the interface. Once an inclusion cleaves, the strong bond allows for transfer of the TiN crack into the ferritic matrix. It was estimated that only 0.0016 wt pct Ti was tied up in the offending inclusions in steel B. This indicates that extended times at high temperatures during the casting of such steels could produce TiN-related toughness deterioration at even modest Ti contents.

    更新日期:2020-01-01
  • Wear Behavior of Plasma Spray Deposited and Post Heat-Treated Hydroxyapatite (HA)-Based Composite Coating on Titanium Alloy (Ti-6Al-4V) Substrate
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2018
    R. V. Valli Kumari,Jyotsna Dutta Majumdar

    The present study concerns a detailed evaluation of wear resistance property of plasma spray deposited composite hydroxyapatite (HA)-based (HA-50 wt pct TiO2 and HA-10 wt pct ZrO2) bioactive coatings developed on Ti-6Al-4V substrate and studying the effect of heat treatment on it. Heat treatment of plasma spray deposited samples has been carried out at 650 °C for 2 hours (for HA-50 wt pct TiO2 coating) and at 750 °C for 2 hours (for HA-10 wt pct ZrO2 coating). There is significant deterioration in wear resistance for HA-50 wt pctTiO2 coating and a marginal deterioration in wear resistance for HA-10 wt pct ZrO2 coating in as-sprayed state (as compared to as-received Ti-6Al-4V) which is, however, improved after heat treatment. The coefficient of friction is marginally increased for both HA-50 wt pct TiO2 and HA-10 wt pct ZrO2 coatings in as-sprayed condition as compared to Ti-6Al-4V substrate. However, coefficient of friction is decreased for both HA-50 wt pct TiO2 and HA-10 wt pct ZrO2 coatings after heat-treated condition as compared to Ti-6Al-4V substrate. The maximum improvement in wear resistance property is, however, observed for HA-10 wt pct ZrO2 sample after heat treatment. The mechanism of wear has been investigated.

    更新日期:2020-01-01
  • Application of MIVM for Sn-Zn System in Vacuum Distillation
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    Lingxin Kong,Bin Yang,Baoqiang Xu,YiFu Li,Yuanshou Hu,Dachun Liu

    The activities of components of Sn-Zn system were predicted based on the molecular interaction volume model (MIVM). The separation coefficients and the vapor–liquid phase equilibrium of Sn-Zn system were also predicted using the MIVM. The predicted results indicated that the content of tin in the vapor phase was 0.000052 wt pct, while in the liquid phase, it was 99.98 wt pct at 1173 K (900 °C). Experimental investigations into the separation of Sn-Zn alloy by vacuum distillation were carried out for the proper interpretation of the predicted results. The effects of vacuum level (15 to 200 Pa), distillation temperatures [873  K to 1273  K (600 °C to 1000 °C)], and soaking time (20 to 60 minutes) were studied. The experimental results indicated that the content of tin in the vapor phase was 0.001 wt pct, while in the liquid phase, it was 99.98 wt pct at 1173 K (900 °C). The experimental results match well with the predicted data, suggesting that the MIVM is a suitable model for Sn-Zn system.

    更新日期:2020-01-01
  • Soldering of Mg Joints Using Zn-Al Solders
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2018
    T. Gancarz,Katarzyna Berent,Wojciech Skuza,Katarzyna Agnieszka Janik

    Magnesium has applications in the automotive and aerospace industries that can significantly contribute to greater fuel economy and environmental conservation. The Mg alloys used in the automotive industry could reduce mass by up to 70 pct, providing energy savings. However, alongside the advantages there are limitations and technological barriers to use Mg alloys. One of the advantages concerns phenomena occurring at the interface when joining materials investigated in this study, in regard to the effect of temperature and soldering time for pure Mg joints. Eutectic Zn-Al and Zn-Al alloys with 0.05 (wt pct) Li and 0.2 (wt pct) Na were used in the soldering process. The process was performed for 3, 5, and 8 minutes of contact, at temperatures of 425 °C, 450 °C, 475 °C, and 500 °C. Selected, solidified solder-substrate couples were cross-sectioned, and their interfacial microstructures were investigated by scanning electron microscopy. The experiment was designed to demonstrate the effect of time, temperature, and the addition of Li and Na on the kinetics of the dissolving Mg substrate. The addition of Li and Na to eutectic Zn-Al caused to improve mechanical properties. Higher temperatures led to reduced joint strength, which is caused by increased interfacial reaction.

    更新日期:2020-01-01
  • Computational modeling of through-thickness dynamic impact response in cross-rolled Ti-6Al-4V plates
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2002
    Bimal K. Kad,Scott E. Schoenfeld,Matthew S. Burkins

    The through-thickness ballistic impact response for extra-low-interstitial (ELI)-grade Ti-6Al-4V crossrolled and heat-treated plates is numerically simulated, taking into account specific material textures. Ballistic tests suggest that the incidence of material plugging is affected by specific thermal/mechanical processing paths above and below the β-transus temperature. Ti-6Al-4V polycrystalline aggregates are nominally textured via routine rolling-deformation and thermal-processing schedules in the α+β or β-phase fields. Thus, realistic processing textures, viz., the basal, transverse, as well as an idealized random texture, are simulated via a two-dimensional (2D) constitutive model for slip and twinning (treated here as pseudoslip) prescribed for the hcp single crystal. The polycrystal is constructed by incorporating the material theory into a finite-element model that explicitly represents a spatial distribution of single crystals. The polycrystalline mechanical response is examined with respect to macroscopic shear loading, such as that which may take place during dynamic punch-through processes. A ranking of the material textures is prescribed via numerically derived measures of external work performed. Results indicate that transverse textures generated by thermal/mechanical processing in the β-phase field are particularly susceptible to impact failures. Such microstructural and orientation-sensitive rankings are a keen marker of material performance and offer a refinement over the quasistatically generated Mil-A-4077 acceptance criterion for ballistic impact applications.

    更新日期:2020-01-01
  • Structure-property correlation of submerged-arc and gas-metal-arc weldments in HY-100 steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1987
    P S Deb,Kenneth D. Challenger,A. E. Therrien

    Structure-property relationships of two HY-100 steel weldments prepared by submerged arc (SAW) and gas metal arc (GMAW) welding processes using identical heat input (2.2 kJ mm-1) have been studied. It has been found that submerged arc welded (SAW) HY-100 steel weldments have a lower weld toughness than welds produced by the gas metal arc welding (GMAW) process. Optical, scanning, and transmission electron microscopy were used in conjunction with microhardness traverses to characterize and compare the various microconstituents that are present in the last weld pass of both weldments. TEM examination revealed the presence of coarse upper bainite, B-II bainite, and carbides in a highly dislocated ferrite matrix as well as in ferrite laths in the SAW weldment, while the GMAW weldment exhibited a typical fine low carbon lath martensite, autotempered martensite, and mixed B-II and B-III bainites which occasionally contained small regions of twinned martensite. The measured cooling rate in the SAW was found to be about 40 pct slower than that in GMAW. It was also found in the SAW that the weld metal inclusion number density was about 25 pct greater than that in GMAW. Micro-hardness traverses exhibited significantly lower hardness (about 50 HV) in the SAW weldment compared with GMAW, but the tempered weld metal microhardness in both the weldments was measured about the same, at 250 HV. The ductile-to-brittle transition temperature (DBTT) of both weldments was determined by Charpy impact test. Based on an average energy criterion, the DBTT of the SAW weldment was 323 K (50 °C) higher than that of the GMAW weldment. This difference in fracture resistance is due to the different weld metal microstructures. The different microstructures most probably result from differences in cooling rate subsequent to welding; however, the SAW weld also has a higher inclusion number density which could promote a higher transformation temperature for the austenite.

    更新日期:2020-01-01
  • Effect of Aluminum Content on Wear Resistance of Hot-Forged Multiphase Steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2016
    Masoud Ibrahim Mohamed,Ahmed Ismail Zaky Farahat,J. A. Al-jarrah

    A medium-carbon steel was alloyed with Mn, Cr, Si, and Al to obtain carbide-free bainite steel. The thermomechanics and chemistry of steel were used to produce medium carbon containing four phases: ferrite, pearlite, bainite, and chromium carbide. The morphologies of different phases were characterized and analyzed by using optical and scanning electron microscopes. An abrasive dry sliding wear (pin on ring) of two types of medium-carbon, hot-forged steels containing different aluminum contents was investigated at different pressures and sliding velocities. The sliding duration time was 30 minutes under dry sliding conditions. The wear rate of Alloy 1 and 2 revealed negligible wear rates at low velocity and pressure. On the other hand, the wear rate highly increased to maximum at maximum velocity and pressure for Alloy 1 and 2. Alloy steel 2 of 2 pct Al revealed a maximum wear rate of 720 mg/min compared with 160.8 mg/min for Alloy 1 contains 1 pct Al. Experimental results showed that increased aluminum content is directly proportional to the ferrite volume fraction, which greatly influences the wear resistance performance and mechanical properties of the two types of steel.

    更新日期:2020-01-01
  • Load Partitioning and Strain-Induced Martensite Formation during Tensile Loading of a Metastable Austenitic Stainless Steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2009
    Peter Hedström,L. E. Lindgren,J. Almer,Ulrich Lienert,Jean Bernier,Mathieu Terner,Magnus Odén

    In-situ high-energy X-ray diffraction and material modeling are used to investigate the strain-rate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and α′ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower α′ martensite fraction observed at fracture for a strain rate of 10−2 s−1, as compared to 10−3 s−1. This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson–Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The α′ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to α′ martensite during loading.

    更新日期:2020-01-01
  • In Situ Thermo-magnetic Investigation of the Austenitic Phase During Tempering of a 13Cr6Ni2Mo Supermartensitic Stainless Steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    A. Bojack,Lie Zhao,P. F. Morris,Jilt Sietsma

    The formation of austenite during tempering of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) was investigated using an in situ thermo-magnetic technique to establish the kinetics of the martensite to austenite transformation and the stability of austenite. The austenite fraction was obtained from in situ magnetization measurements. It was found that during heating to the tempering temperature 1 to 2 vol pct of austenite, retained during quenching after the austenitization treatment, decomposed between 623 K and 753 K (350 °C and 480 °C). The activation energy for martensite to austenite transformation was found by JMAK-fitting to be 233 kJ/mol. This value is similar to the activation energy for Ni and Mn diffusion in iron and supports the assumption that partitioning of Ni and Mn to austenite are mainly rate determining for the austenite formation during tempering. This also indicates that the stability of austenite during cooling after tempering depends on these elements. With increasing tempering temperature the thermal stability of austenite is decreasing due to the lower concentrations of austenite-stabilizing elements in the increased fraction of austenite. After cooling from the tempering temperature the retained austenite was further partially decomposed during holding at room temperature. This appears to be related to previous martensite formation during cooling.

    更新日期:2020-01-01
  • Precipitation Modeling in Nitriding in Fe-M Binary System
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2016
    Yusaku Tomio,Goro Miyamoto,Tadashi Furuhara

    Precipitation of fine alloy nitrides near the specimen surface results in significant surface hardening in nitriding of alloyed steels. In this study, a simulation model of alloy nitride precipitation during nitriding is developed for Fe-M binary system based upon the Kampmann–Wagner numerical model in order to predict variations in the distribution of precipitates with depth. The model can predict the number density, average radius, and volume fraction of alloy nitrides as a function of depth from the surface and nitriding time. By a comparison with the experimental observation in a nitrided Fe-Cr alloy, it was found that the model can predict successfully the observed particle distribution from the surface into depth when appropriate solubility of CrN, interfacial energy between CrN and α, and nitrogen flux at the surface are selected.

    更新日期:2020-01-01
  • Effects of temperature and shot peening on S-N behavior of a PM Ni-base superalloy UDIMET 720
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2004
    Jian-shu Luo,Paul Bowen

    Fatigue S-N (stress vs life) curve behavior for a powder metallurgy (PM) Ni-base superalloy UDIMET 720 in both polished and shot-peened surface conditions was investigated at room temperature and 600 °C in air. Tests were carried out under four-point bending at a load ratio of 0.1 and a frequency of 10 Hz. At 600 °C, an offset S-N curve was found for both polished and shot-peened surface conditions. This offset S-N curve is deduced to be controlled by the location of crack nucleation sites. Observations and deductions of crack nucleation sites, crack nucleation life, crack closure, environmental attack, and cyclic softening and hardening have been used to explain the experimental results.

    更新日期:2020-01-01
  • Improvement of Drawability of Titanium-Stabilized Interstitial-Free Steel by Optimization of Process Parameters and Texture
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2008
    Kumkum Banerjee,Anil K. Verma,T. Venugopalan

    AbstractA detailed study on the effect of cold rolling and annealing temperature on the texture and drawability of Ti-stabilized interstitial-free (IF) steels have been made with a view to achieving high drawability. The presence of shear type and cold-deformation type of textures in the hot bands of 3.8-, 4.3- and 4.5-mm thickness has been attributed to finish rolling below the Ar3 temperature. The 4.5-mm hot band was selected for further studies as it showed a strong γ fiber. Cold rolling of the hot band was done in the range of 60 to 90 pct, followed by batch annealing in the range of 660 °C to 750 °C. For a particular annealing temperature, a maximum in the intensity of $$ {\left\{ {{\text{111}}} \right\}}{\left\langle {{\text{110}}} \right\rangle } $$ component, and in average normal anisotropy, an rm value was observed with the increase in cold reduction, followed by a drop with further cold reduction. The results are discussed in terms of orientation distribution function (ODF), recrystallization behavior, and precipitation of FeTiP, (Ti, Mn) S, and TiC particles. Fine FeTiP-type precipitates in the grains and at the grain boundaries in samples annealed at 660 °C, as well as samples associated with (Ti, Mn)S in samples annealed at 750 °C, were found to be detrimental for the development of beneficial γ fiber and improved drawability, while coarse FeTiP-type precipitates in 80 pct cold-reduced samples annealed at 680 °C and 710 °C resulted in maximum rm values of 2.29 and 2.25, respectively. The dissolution of TiC at an annealing temperature of 750 °C adversely affected drawability due to the solute drag effect of solute carbon. An optimized combination of cold reduction and annealing temperature has been established for achieving a uniform γ fiber along with high rm values.

    更新日期:2020-01-01
  • Microstructural evolution of a nanocrystalline Ti−47Al−3Cr alloy during annealing in the α+γ-phase field
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1999
    M. L. Öveçoglu,O. N. Senkov,N. Srisukhumbowornchai,F. H. Froes

    Prealloyed, gas-atomized (GA) Ti−47Al−3Cr alloy powder, containing about 70 pct of the α2 (Ti3Al) phase and 30 pct of the γ (TiAl) phase, was fully amorphized by mechanical alloying. The amorphous phase was stable during heating to 600°C, but decomposed at higher temperatures, with an exothermic reaction peak at 624°C as the material transformed to a mixture of α2 and γ and then to a fully γ structure at 722°C. A nanocrystalline compact with a mean grain size of 42 nm was obtained by hot isostatic pressing (HIP'ing) of the amorphous powder at 725°C. Isothermal annealing experiments were conducted in the two-phase α+γ field, at 1200°C, using holding times of 5, 10, 25, and 35 hours, followed by air cooling. The X-ray diffractometry and analytical transmission electron microscopy investigations carried out on annealed and air-cooled specimens revealed only the presence of the γ grains, which coarsened on annealing. Initially, the grains grew, followed by a saturation stage after annealing for 25 hours, with a saturation grain size of about 1 μm. This grain growth and saturation behavior can be described with a normal grain growth mechanism in which a permanent pinning force is taken into account. Twins formed in the γ grains as a result of annealing and air cooling and exhibited a common twinning plane of (111) with the matrix phase. The minimum γ grain size in which twinning occurred in the annealed specimens was determined to be 0.25 μm, which suggests that twinning is energetically unfavorable in the nanometer-sized grains.

    更新日期:2020-01-01
  • Interface stability during displacement reactions between Cu2O and Co1−XFeX alloys at 1223 K
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2002
    S. N. S. Reddy,Lovell B. Wiggins

    The stability of the reactive interface during the solid-state displacement reaction, Cu2O+Co1−XFeX=2Cu+(Co1−XFeX)O, is studied as a function of Co-Fe alloy composition at 1223 K. For X≤0.03, the reaction zone has a layered structure, and the cation diffusion in (Co, Fe)O is the rate-limiting step. The interface is unstable in the early stages of the reaction; the instability decreases with time as the oxide thickness increases, and the interface becomes planar at long times. The time required for the attainment of interface planarity increases with the value of X. The reaction kinetics are consistent with the available cation-diffusion data in (Co, Fe)O. For X≥0.045, the product zone is a composite of Cu+(Co, Fe)O, and the rate is limited by the oxygen transport in copper. The transition to interface instability occurs when the oxide can support a cation flux that exceeds the maximum possible oxygen flux in copper. During the reaction, composition gradients develop in (Co, Fe)O because of higher diffusion rates for iron than for cobalt.

    更新日期:2020-01-01
  • Solidification of Highly Undercooled Hypereutectic Ni-Ni3B Alloy Melt
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    Feng Liu,Junfeng Xu,Di Zhang,Zengyun Jian

    The solidification of undercooled Ni-4.5 wt pct B alloy melt was investigated by using the glass fluxing technique. The alloy melt was undercooled up to ΔTp ~ 245 K (245 °C), where a mixture of α-Ni dendrite, Ni3B dendrite, rod eutectic, and precipitates was obtained. If ΔTp < 175 K ± 10 K (175 °C ± 10 °C), the solidification pathway was found as primary transformation and eutectic transformation (L → Ni3B and L → Ni/Ni3B); if ΔTp ≥ 175 K ± 10 K (175 °C ± 10 °C), the pathway was found as metastable eutectic transformation, metastable phase decomposition, and residual liquid solidification (L → Ni/Ni23B6, Ni23B6 → Ni/Ni3B, and Lr → Ni/Ni3B). A high-speed video system was adopted to observe the solidification front of each transformation. It showed that for residual liquid solidification, the solidification front velocity is the same magnitude as that for eutectic transformation, but is an order of magnitude larger than for metastable eutectic transformation, which confirms the reaction as Lr → Ni/Ni3B; it also showed that this velocity decreases with increasing ΔTr, which can be explained by reduction of the residual liquid fraction and decrease of Ni23B6 decomposition rate.

    更新日期:2020-01-01
  • Cellular Precipitation at a 17-7 PH Stainless Steel Interphase Interface During Low-Temperature Nitridation
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    D. Wang,Frank Ernst,Harold Kahn,Arthur H. Heuer

    AbstractCellular precipitation of Cr-rich nitrides was observed at an austenite–ferrite interface in 17-7 PH stainless steel after low-temperature nitridation. Fine-scale lamellar rocksalt-structured nitride (MN1−x, M: randomly distributed Fe, Cr, and Al) was identified at the interfaces between austenite and ferrite by local-electrode atom-probe tomography and transmission electron microscopy. The small size and spacing of the nitride lamellae reflect the low mobility of substitutional atoms under the conditions of low-temperature nitridation. Nitrides of the same structure were formed within the ferrite grain as extremely small particles. The face-centered cubic nitride precipitates in the Bain orientation relationship with the ferrite.

    更新日期:2020-01-01
  • Phase transitions and microstructure of a laser-induced steel surface alloying
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1997
    Alex Glozman,Menachem Bamberger

    Alloying the surface of AISI 1045 steel with CrB by laser irradiation causes partial dissolution of the chromium boride in the melt and the formation of different borides of Fe and Cr in the treated layer. At a low laser scan velocity (0.01 m/s), the dissolution of CrB is almost complete, and the microstructure and properties of the top layer are uniform. At a higher scan velocity (0.05 m/s), a large number of CrB particles remain undissolved in the layer, and its properties are heterogeneous. The matrix consists of columns of iron boride, with up to 20 pct Cr dissolved in it, and between them a eutectic containing α-Fe and chromium-boride with dissolved Fe. Iron boride grows on a transitional layer of Cr2B coating the surface of residual CrB particles, which cannot serve as nucleation sites because of the incompatibility of their crystal structure with that of (Fe,Cr)2B.

    更新日期:2020-01-01
  • In situ studies of precipitate formationin Al-Pb monotectic solidification by X-ray transmission microscopy
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1997
    William F. Kaukler,Franz Rosenberger,Peter A. Curreri

    Al-1.5 wt pct Pb monotectic alloys were unidirectionally solidified. X-ray transmission microscope (XTM) observations, both during and after solidification, revealed various new morphological/compositional features in the melt and solid. In the melt, nonuniform lead-rich interfacial segregation layers and droplets were observed to form well ahead of the interface. In the solid, periodic striae formed at translation/solidification velocities as low as 6 × 10−6 m/s. The striae shape does not replicate that of the interface. The striae spacing decreases from 4 to 2 × 10−4 m with an increasing solidification rate between 6 and 16 × 10−6 m/s. High resolution postsolidification XTM examination reveals that these striae consist of Pb-rich particles of 2 to 3 × 10−6 m diameter. At translation/solidification velocities below 6 × 10−6 m/s, Pb incorporation into the solid occurs in the form of continuous fibers and strings of particles of about 5 × 10−6 m diameter. Bands, parallel to the interface, in which these fibers were aligned in the solidification direction, alternated with bands of poor fiber alignment. The width of these bands is comparable to the striae spacings obtained at the high solidification rates.

    更新日期:2020-01-01
  • Effects of Surface Oxide on the Nitridation Behavior of Aluminum Particles
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2014
    S. H. Kim,Jae Hong Noh,Jae-Pyoung Ahn,Jae-Chul Lee,Jung Hoon Kwon,Jaegab Lee,H. R. Yang,Kon Bae Lee

    A detailed transmission electron microscopy study coupled with electron energy loss spectroscopy was conducted on AlN formed by the direct nitridation of Al particles under nitrogen atmosphere. The nitridation mechanism comprised two steps: the formation of AlN shell on Al particles and the growth of AlN with a lath type in Al droplets. Here, we found that the surface oxide layer of the Al particles acted as a channel layer, which supplied nitrogen in the atomic state to liquid Al, after being transformed into a thin AlON layer during the initial nitridation. In the Al particles, the inward growth of AlN with a shell structure occurred at the sub layer of the AlON layer. On the other hand, the extracted liquid Al droplets formed after the cracking of the AlN shell rested on the Al particles surrounded by the AlON layer. The nitridation of the droplets began at the interface between the Al particle and droplet and not at the free surface and grew outward from the droplet. Herein, based on the observation of the AlON layer formation, we propose a new mechanism for the nitridation of Al particles.

    更新日期:2020-01-01
  • The effect of consolidation temperature on microstructure and mechanical properties in powder metallurgy-processed 2XXX aluminum alloy composites reinforced with SiC particulates
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1997
    Keesam Shin,Dongsup Chung,Sunghak Lee

    The effects of consolidation temperature on the development of microstructure and resulting mechanical properties of 2XXX aluminum composites were studied in an effort to fabricate composites with enhanced properties. Type 2009 and 2124 aluminum composites reinforced with 15 pct SiC particulates were produced at four different consolidation temperatures, i.e., 560 °C, 580 °C, 600 °C, and 620 °C, followed by extrusion at 450 °C. The 2124 Al-SiCp composites consolidated at 560 °C showed the most homogeneous and the finest microstructures with the best mechanical properties, which were even better than the whisker-reinforced counterparts. All the results of the tensile tests, hardness tests, in situ scanning electron microscope (SEM) observations of the fracture process, and the apparent fracture toughness indicated that the prominent mechanical property improvement observed in the 2124 Al-SiCp was associated largely with the reduction of volume fraction of the detrimental coarse and brittle manganese-containing particles, as well as grain refinement. The detrimental manganese-containing particles that were routinely observed in the 2124 Al-SiC composites were very effectively refined by the reduction of consolidation temperature, and they rather contributed to the overall mechanical properties of the composites through Orowan-type strengthening and grain growth inhibition.

    更新日期:2020-01-01
  • Effects of aluminum content on the mechanical properties of a 9Cr-0.5Mo-1.8W steel
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 1997
    Hiroo Naoi,Masahiro Ohgami,Xj Liu,T. Fujita

    The effects of aluminum content on mechanical properties of a 9Cr-0.5Mo-1.8W steel have been investigated. It was found that aluminum addition had a beneficial effect on toughness, but significantly reduced the creep resistance of the steel, especially on the long-term side. Examination of the microstructure and precipitation characteristics revealed that almost all of the aluminum added existed as AIN-type nitrides after normalizing and tempering. The undissolved AIN in high aluminum steels resulted in a dramatic refinement of prior austenite grains, which contributed to the improvement of toughness and was also partially responsible for the decreased creep rupture strength. The formation of AIN suppressed the precipitation of VN-type nitride; AIN also provided formation sites for Nb(C, N) and M23C6 type, which had an equivalent effect to the coalescence of these precipitates on AIN, resulting in the reduction of precipitate density and, therefore, decreased creep resistance.

    更新日期:2020-01-01
  • The gibbs-thomson effect in dilute binary systems
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2002
    Ma Qian

    A constructed molar Gibbs energy diagram was used to introduce a general description of the Gibbs-Thomson effect in dilute binary system. The analysis was based on the assumption that the common tangent approach is applicable to the solid-solid systems analyzed. The solubility of a precipitate, which was commonly referred to as the composition of the matrix in equilibrium with the precipitate in the presence of a curved interface, was studied. The equilibrium between the matrix and the precipitate was illustrated by constructing a molar Gibbs free energy diagram. The analysis was found to approximate the solid-solid systems, as if the matrix were liquid.

    更新日期:2020-01-01
  • The effect of lamellar morphology on tensile and high-cycle fatigue behavior of orthorhombic Ti-22Al-27Nb alloy
    Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2004
    Masuo Hagiwara,Satoshi Emura,Aya Araoka,Seung Jin Yang,Soo Woo Nam

    The room-temperature tensile and high-cycle fatigue (HCF) behavior of orthorhombic Ti-22Al-27Nb alloy with varying lamellar morphology was investigated. Varying lamellar morphology was produced by changing the cooling rate after annealing in the single B2 phase region. A slower cooling rate of 0.003 K/s, for example, resulted in several large packets or colonies of similarly aligned O-phase lamellae and a nearly continuous massive α2 phase at the prior B2 grain boundaries, while a faster cooling rate of 0.1 K/s led to the refinement of colony sizes and the O-phase lamellae. The interface of O-phase lamellae and B2 phases was semicoherent. Water quenching produced a very fine tweed-like microstructure with a thin continuous O phase at the prior B2 grain boundaries. The 0.2 pct yield stress, tensile strength, and HCF strength increased with increasing cooling rate. For example, the tensile strength and HCF strength at 107 cycles of 0.003 and 0.1 K/s-cooled were 774 and 450 MPa, and 945 and 620 MPa, respectively. Since the fatigue ratio, which is the ratio of HCF strength at 107 cycles to tensile strength, did not show a constant value, but instead increased with increasing cooling rate, part of the fatigue improvement was the result of improved resistance to fatigue associated with the microstructural refinement of the lamellar morphology. Fatigue failure occurred by the subsurface initiation, and every initiation site was found to contain a flat facet. Concurrent observation of the fatigue initiation facet and the underlying microstructure revealed that the fatigue crack initiated in a shear mode across the colony, irrespective of colony size, indicating that the size of the initiation facet corresponded to that of the colony. Therefore, the colony size is likely a major controlling factor in determining the degree of fatigue improvement due to the microstructural refinement of lamellar morphology. For the water-quenched specimens, fatigue crack initiation appeared to be associated with shear cracking along the boundary between the continuous grain boundary O phase and the adjacent prior B2 grain.

    更新日期:2020-01-01
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