• 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：2020-01-21
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• 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
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-05
Christian Hagenlocher, Daniel Weller, Rudolf Weber, Thomas Graf

In the original article the indefinite integral sign of the solidification path is missing in Eq. [5].

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-06-03
Kazuyuki Shimizu, Hiroyuki Toda, Kentaro Uesugi, Akihisa Takeuchi

The local deformation and fracture behavior of high-Zn Al-Zn-Mg(-Cu) alloys under hydrogen influence were investigated by in situ tests through synchrotron X-ray tomography. Intergranular and quasi-cleavage fractures were induced by hydrogen, and strain localization by the presence of cracks was not observed by 3D strain mapping. These results suggest that the strain localization at the crack tip is smaller than the measurement limit of 3D strain mapping. The average crack-tip-opening displacements, which are one of the crack driving forces specified by fracture mechanics, directly measured from the tomographic slice were 0.14 and 0.23 μm for intergranular cracks and quasi-cleavage cracks, respectively. The crack driving forces of the intergranular and quasi-cleavage cracks were small. The local deformation behavior at the crack tips was analyzed based on fracture mechanics. The local deformation field of the crack tip, which was characterized using the Rice–Drugan–Sham (RDS) solution rather than the Hutchinson–Rice–Rosengren (HRR) solution, was located within 20 μm of the crack tip, and its size was limited. The results of this work clarify that the intergranular and quasi-cleavage crack growths are caused by small driving forces; however, this behavior is not perfectly brittle, accompanying local deformation at the crack tip.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-10-28
Lei Jiang, Huadong Fu, Changsheng Wang, Weidong Li, Jianxin Xie

Two different thermo-mechanical processing routes, single-cold-rolling and double-cold-rolling, are adopted to process a Cu-Ni-Si alloy, and their effects on the microstructure and properties of the alloys are investigated. While keeping identical aging treatments and equivalent total cold-rolling deformation, 45-minute final aging at 450 °C endows the double-cold-rolling-processed alloys with a tensile strength of 754 ± 12 MPa, higher than 691 ± 3 MPa for the single-cold-rolling-processed alloys, whereas their electrical conductivities are close (~ 39 pct IACS). The final aging at 450 °C for 4 hours, on the other hand, renders the double-cold-rolling-processed alloy an electrical conductivity of 52.6 pct IACS, greater than 43.7 pct IACS for the single-cold-rolling-processed alloy, whereas their strengths are approximately identical (~ 705 MPa). The superior mechanical and electrical properties in the double-cold-rolling-processed alloy with the final aging time from 45 minutes to 4 hours are attributed to the dissolution of large precipitates during the second cold rolling followed by the acceleration of fine and uniformly dispersed precipitates in the final aging. Finally, the effects of dislocations, grain boundaries, solute atoms, and precipitates on the mechanical and electrical properties of the examined Cu-Ni-Si alloy are discussed on the theoretical basis, which can provide guidelines to further processing optimization.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-11
Hengcheng Liao, Heting Xu, Jingfan Tang, Shihui Huo, Daoqiong Huang, Hui Chen

Abstract The effect of repetitive high-stress loading (RHSL) at ultralow temperature on the microstructure and mechanical properties of S04 martensitic steel was studied. RHSL significantly increases the yield strength of S04 steel from 1220 to 1650 MPa and raises the tension elastic modulus from 170 to 207.5 GPa with small plastic deformation. This most efficient strengthening mechanism involves the evolution of dislocation patterns and the formation of martensite twins.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-11
Xiao Tao, Allan Matthews, Adrian Leyland

Abstract Chromium, as a strong nitride-forming element, is widely regarded to be an “essential” ingredient for the formation of a nitrogen-expanded lattice in thermochemical nitrogen diffusion treatments of austenitic (stainless) steels. In this article, a proprietary “chrome-free” austenitic iron-nickel alloy, Invar® 36 (Fe-36Ni, in wt pct), is characterized after triode plasma nitriding (TPN) treatments at 400 °C to 450 °C and compared with a “stainless” austenitic counterpart RA 330® (Fe-19Cr-35Ni, in wt pct) treated under equivalent nitriding conditions. Cr does indeed appear to play a pivotal role in colossal nitrogen supersaturation (and hence anisotropic lattice expansion and superior surface hardening) of austenitic steel under low-temperature (≤ 450 °C) nitrogen diffusion. Nevertheless, this work reveals that nitrogen-induced lattice expansion occurs below the nitride-containing surface layer in Invar 36 alloy after TPN treatment, implying that Cr is not a necessity for the nitrogen-interstitial induced lattice expansion phenomenon to occur, also suggesting another type of γN.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-18
A. F. Brust, E. J. Payton, V. Sinha, V. A. Yardley, S. R. Niezgoda

Detailed analysis of the characteristics a martensite structure inherits from the parent austenite phase requires knowledge of the crystallographic orientation relationship between austenite and martensite, which varies with composition for steel alloys. The orientation relationship is typically observed to exhibit a significant degree of variability, such that measurements from each variant occupy a range of orientations within the transformed pole figure, complicating characterization of the orientation relationship. Here, we present a Bayesian methodology to measure the orientation relationship on martensite EBSD data from four different steels and a binary Fe-Ni alloy. The number of variants that must be exhibited for an accurate measurement as well as robustness to noisy data for this approach are investigated. The Bayesian approach is found to produce results which compare favorably to those from prior work while being more easily automatable.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-10-16
Z. H. Dong, D. Sergeev, D. Kobertz, N. D’Souza, S. Feng, M. Müller, H. B. Dong

Vaporization and its associated surface defect formation have become one of the most important challenges in manufacturing single-crystal components. During the kinetic-influenced casting and solution heat treatment of Ni-base superalloys, elements undergo processes of vaporization and deposition causing unpredictable defects. To quantitatively examine the vaporization phenomenon, partial vapor pressures of Ni, Al and Cr in Ni-base alloys were measured in the γ phase over the temperature range of 1473 K to 1650 K using Knudsen effusion mass spectrometry. Experimental results showed that the partial pressure of Al is about two orders of magnitude lower than that of Ni and five times lower than that of Cr, revealing that the vaporization of Al is almost negligible compared with those of Ni and Cr at solution heat treatment temperatures. Variation of partial pressures during homogenization of the as-cast Ni-base alloys was measured in long-term isothermal experiments at 1573 K. It was found that Cr vapor pressure decreases by a factor of two in the first 20 hours whereas the Ni and Al remain nearly constant.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-11
Q. C. Fan, M. Y. Sun, Y. Y. Wang, K. H. Sun, X. D. Cao, H. B. Peng, S. K. Huang, Y. H. Zhang, Y. H. Wen

Abstract The phase transformation and recovery stress of pre-deformed Ni47Ti44Nb9 alloy are systematically investigated during constrained heating, cooling and thermal cycling. Recovery stress is determined by a phase transformation, thermal expansion, and contraction. Reverse martensitic transformation occurs during constrained heating and then results in a sharp increase in the recovery stress. Meanwhile, the wide phase transformation hysteresis shrinks during thermal cycling. A few martensitic transformations gradually occur across a wide temperature range during constrained cooling, resulting in a negative decreasing stage or a wide plateau of recovery stress. When cooled further to a critical value of 20 °C, the recovery stress and temperature follow the Clausius–Clapeyron equation, and large amounts of martensitic transformations appear, resulting in the sharp decrease of the recovery stress.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-04
Arun Sundar Sundaram Singaravelu, Jason J. Williams, Harsh Dev Goyal, Sridhar Niverty, Sudhanshu S. Singh, Tyler J. Stannard, Xianghui Xiao, Nikhilesh Chawla

Abstract In situ three-dimensional X-ray synchrotron tomography was used to visualize and quantify the fatigue crack initiation and growth from corrosion pits in high strength aluminum alloys. Corrosion pitted Al 7075 and Al 7475 samples of peak-aged, over-aged, and highly over-aged conditions were prepared by soaking in 3.5 wt pct NaCl solution for fifteen days. These samples were fatigue tested in situ in 3.5 wt pct NaCl solution using synchrotron X-ray tomography to analyze the fatigue crack initiation and growth characteristics (4D). Increases in maximum pit depth and fatigue crack growth rate variability were found with increased aging. A detailed analysis of crack morphology and deflection, as a function of aging, was carried out and it discussed.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-04
Longyi Li, Jun Wang, Jing Yan, Hongyuan Fan, Bo Zeng, Xiaoying Li, Hanshan Dong

Abstract Time-dependent experiments were carried out to study the corrosion behavior of AISI 304 austenitic stainless steel before and after low-temperature oxy-nitriding in HCl solution. The weight loss of the untreated sample was higher than that of the nitrided sample after HCl corrosion. When immersed for a short time, the nitrided sample remained relatively intact, while when immersed for a long time, the nitrogen-rich layer was damaged. XPS analysis showed that the passive film of the low-temperature oxy-nitrided sample was complete. The structure of passive film on the LTON sample was characterized by Mott–Schottky test, and the effect of nitrogen on the corrosion resistance of the material was discussed. The wear test results show that the oxy-nitrided samples after HCl immersion corrosion still maintained high wear resistance.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-10-25
Güven Kurtuldu, Philippe Jarry, Michel Rappaz

Abstract The effect of minute Cr additions on dendritic growth directions in Al-20 wt pct Zn alloy has been investigated. As first evidenced by Gonzales and Rappaz (Metall Mater Trans A 37:2797–2806, 2006) Al-Zn alloys exhibit a Dendrite Orientation Transition (DOT), from 〈100〉 below 25 wt pct Zn to 〈110〉 above 60 wt pct, regardless of the solidification speed. The DOT has been interpreted as a modification of the solid–liquid interfacial energy anisotropy (Gonzales and Rappaz, 2006; Haxhimali et al. in Nat Mater 5:660–664, 2006). However, 0.02 to 0.1 wt pct addition of Cr in Al-20 wt pct Zn drastically modifies the dendrite trunk direction from 〈100〉 to 〈110〉 at low solidification speed, typically 200 μm/s. Even more surprising, 〈100〉 dendrite trunks are retrieved in Al-20 wt pct Zn-0.1 wt pct Cr when the speed is increased to 1000 μm/s, but with the concurrent formation of twinned dendrites. Minute additions of Cr have been reported recently to promote icosahedral short range order (ISRO) in liquid Al-Zn, thus reducing the atomic mobility (Kurtuldu et al. in Acta Mater 115:423–433, 2016) and modifying the nucleation kinetics (Kurtuldu et al. in Acta Mater 61:7098–7108, 2013). The present results indicate that ISRO also modifies the attachment kinetics of icosahedral clusters rather than individual atoms, and is most likely responsible of growth direction change in Al-Zn-Cr alloy and of twinned dendrites formation.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-10-22
A. G. Sheinerman, M. Yu. Gutkin

Abstract A model is proposed that describes plastic deformation in metal/graphene composites with a bimodal grain size distribution of the metallic matrix. Within the model, dislocation pile-ups are generated in large grains at Frank–Read sources, and their stresses promote dislocation motion within the nanocrystalline/ultrafine-grained phase. Also, the presence of graphene gives rise to the mechanisms of strengthening, such as the load transfer to graphene platelets, thermal-mismatch-induced strengthening and Orowan strengthening, as well as to back stress hardening. We demonstrated that the strengthening and strain hardening in bimodal metal/graphene composites are dominated by the Orowan strengthening and back stress hardening. The results also indicate that regardless of the lateral size of graphene platelets, bimodal metal/graphene composites can simultaneously have high yield strength and large uniform deformation but the values of the yield strength and critical uniform deformation are higher in the case of small graphene platelets.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-01
Ying Lu, Luke Walker, Menachem Kimchi, Wei Zhang

Abstract Press-hardened boron steels with ultrahigh strength (above 1500 MPa) are widely used in crash-sensitive safety components in automobiles. Joining such steels to aluminum alloys is challenging due to various factors including the steel’s tenacious Al-Si coating. A novel application of ultrasonic plus resistance spot welding was developed for such dissimilar metal joining. The nugget formation and the interface microstructure especially intermetallics formed were correlated to the joint strength, ductility and failure behavior.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-11-21
Xinyu Zhang, Chuanwei Li, Haozhang Zhong, Xudong Yang, Jianfeng Gu

This study investigates the microstructure morphology in a single-track wall of Ti-47Al-2Cr-2Nb alloy produced by direct laser deposition. The as-deposited wall mainly exhibited an alternative-band microstructure containing a dendrite band and α2/γ lamellar band, which is considered to result from the influence of the heat affected zone. A tailoring method was proposed and alternative-band microstructures with various equiaxed colony fractions, and even nearly fully equiaxed colony microstructures, were successfully obtained.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-07-09
Ya-Peng Yu, Hiromitsu Furukawa, Noritaka Horii, Mitsuhiro Murayama

Integrating in situ deformation and electron tomography (ET) techniques allows us to visualize the materials’ response to an applied stress with nanometer spatial resolution. The capability of structural, chemical, and morphological characterization in three-dimension real time and at sub-microscopic levels alleviates several persistent problems of two-dimensional imaging such as the projection effect and postmortem appearance. On the other hand, implementing deformation mechanism introduces additional experimental constraints that could influence the accuracy of the reconstructed volumes in a different way. To materialize quantitative and statistically relevant microstructure interpretation by time-resolved ET, we evaluated several key parameters such as angular tilt range, tilt increment, and reconstruction algorithms to characterize their influences on the accuracy of size and morphology reproducibility.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-10-25
Abigail K. Ackerman, Alexander J. Knowles, Hazel M. Gardner, André A. N. Németh, Ioannis Bantounas, Anna Radecka, Michael P. Moody, Paul A. J. Bagot, Roger C. Reed, David Rugg, David Dye

Abstract The kinetics of primary α-Ti colony/Widmanstätten plate growth from the β are examined in Ti-6246, comparing a simple quasi-analytic model to experiment. The plate growth velocity depends sensitively both on the diffusivity D(T) of the rate-limiting species and on the supersaturation around the growing plate. These result in a maxima in growth velocity around 40 K below the transus, once sufficient supersaturation is available to drive the plate growth. In Ti-6246, the plate growth velocity was found to be around 0.32 μm min−1 at 850 °C, which was in good agreement with the model prediction of 0.36 μm min−1. The solute field around the growing plates, and the plate thickness, was found to be quite variable, due to the intergrowth of plates and soft impingement. This solute field was found to extend to up to 30 nm, and the interface concentration in the β was found to be around 6.4 at. pct Mo. It was found that the increasing O content from 500 to 1500 wppm will have minimal effect on the plate lengths expected during continuous cooling; in contrast, Mo approximately doubles the plate lengths obtained for every 2 wt pct Mo reduction. Alloys using V as the β stabilizer instead of Mo are expected to have much faster plate growth kinetics at nominally equivalent V contents. These findings will provide a useful tool for the integrated design of alloys and process routes to achieve tailored microstructures.

更新日期：2019-12-21
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-19
Shaheen Fatima Anis, Ahmad O. Mostafa, Nidal Hilal, Raed Hashaikeh

In this study, novel nano crystalline composite strings made from mixed nickel-tungsten oxides (NiWO4-WO3-WO2.9) have been fabricated. The NiWO4-WO3 fibers produced by the electrospinning method were post treated in an argon atmosphere at 800 °C which yielded NiWO4-WO3-WO2.9 nanocrystals attached together forming a string-like structure. The presence of WO2.9 phase was confirmed by both the XRD and TEM diffraction pattern analysis. String morphology and structure were found to change with different post treatment conditions such as by changing the calcination temperature from 550 °C under oxygen to 800 °C under pure argon atmosphere. This material was investigated for electrocatalytic hydrogen evolution reaction (HER) in 0.5 M H2SO4 and 0.1 M KOH electrolytes. These composite strings showed good electrocatalytic activity compared to the NiWO4-WO3 fibers reported previously (Anis et al. in J. Mater. Sci. 52:7269–7281, 2017). It was concluded that the presence of WO2.9 phase increases the electrocatalytic activity of the catalyst as compared to the NiWO4-WO3 fibers with overpotentials as low as 40 and 50 mV in 0.5 M H2SO4 and 0.1 M KOH, respectively.

更新日期：2019-12-19
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-19
Yong Li, Xue Wang

In this work, simulated CGHAZ of T23 steel was produced via a thermomechanical simulator, and then the CGHAZ specimens were aged at 650 °C for 0 to 240 hours to simulate the microstructure evolution of as-welded CGHAZ during service. Microstructure change and carbide precipitation were observed by OM, SEM, EBSD and TEM + EDS. Carbide precipitation kinetics in T23 steel at 650 °C was calculated for comparison with the experiment results. The hardness change of CGHAZ during aging was detected, and the effect of microstructure evolution on hardness was analyzed. The results showed that the CGHAZ of T23 steel exhibited a mixed microstructure of martensite and bainite with high hardness in as-welded condition. After aging at 650 °C, the microstructure recovered, recrystallization occurred, the dislocation density decreased, and the lath width increased. Consequently, the hardness dropped, the drop depending on the aging time. In the early stage of aging (before 24 hours), the precipitations inside the grain were mainly M3C, M7C3 and a small number of M23C6 carbides, while the precipitation at the grain boundaries was M23C6. The precipitation of M23C6 caused the hardness to drop rapidly. When aged for 24 to 48 hours, MX precipitated inside grains extensively. The precipitation hardening produced by MX could slow down the decline of hardness. As the aging proceeded, carbide precipitated and transformed as follows: M3C → M3C + M7C3 + M23C6 → M3C + M7C3 + M23C6 + MX → M23C6 + MX + M6C. W-rich carbides precipitated in some grain boundaries of CGHAZ during aging, which may be related to the W segregation at those grain boundaries.

更新日期：2019-12-19
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-18
F. D. León-Cázares, C. Kienl, C. M. F. Rae

Dislocations are crystal defects responsible for plastic deformation, and understanding their behavior is key to the design of materials with better properties. Electron microscopy has been widely used to characterize dislocations, but the resulting images are only two-dimensional projections of the real defects. The current work introduces a framework to determine the sample and crystal orientations from micrographs with planar deformation features (twins, stacking faults, and slip bands) in three or four non-coplanar slip systems of an fcc material. This is then extended into a methodology for the three-dimensional reconstruction of dislocations lying on planes with a known orientation that can be easily coupled with a standard Burgers vector analysis, as proved here in a nickel-based superalloy. This technique can only be used in materials that show specific deformation conditions, but it is faster than other alternatives as it relies on the manual tracing of dislocations in a single micrograph.

更新日期：2019-12-19
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-17
Kwai S. Chan

Engineering alloys such as Ni-based alloys, Al-alloys, and steels often contain non-metallic inclusions in their microstructures. These inclusions, which include oxide particles, carbides, and intermetallic particles, are introduced during component manufacturing processes such as casting, powder-metallurgy, or additive manufacturing methods. The presence of inclusions in the microstructure can promote fatigue crack nucleation by competing against slipband nucleation and reduce fatigue life performance of an engineering component. While it has been reported in many occasions, the competition between fatigue crack nucleation at inclusions and slipbands is still not well understood. In this article, the conditions for the concurrent occurrence of fatigue crack nucleation at inclusions and slipbands are analyzed theoretically. The analysis indicates that there exists a critical inclusion size (diameter) below which there is no fatigue life debit due to crack initiation at inclusions and above which a transition from slip-induced to inclusion-induced crack nucleation occurs. The low-cycle fatigue life model is applied to Ni-based superalloys and the model predictions are compared against experimental data from the literature to assess the dependence of the critical inclusion size on the slip morphology, grain size of the matrix, and the shear modulus of the inclusion.

更新日期：2019-12-18
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-17
X. J. Wu, X. Z. Zhang, R. Liu, M. X. Yao

In this study, the deformation-mechanism-based true-stress (DMTS) creep model is modified to include oxidation influence on the long-term creep performance of modified 9Cr-1Mo steels. An area-deduction method is introduced to evaluate oxide scale formation on the creep coupons, which is incorporated into the DMTS model formulated based on intragranular dislocation glide (IDG), intragranular dislocation climb (IDC), and grain boundary sliding (GBS) mechanisms, in modifying the true stress. Thus, the modified DMTS model can not only describe the creep curve, but also predict the long-term creep life and failure mode, which is shown to be in good agreement with the creep data generated in the authors’ laboratory as well as by the National Institute for Materials Science (NIMS) of Japan for long-term (> 104 hours) creep life prediction on Grade 91 steels. In particular, the predictability of the model is demonstrated in comparison with the Larson–Miller parameter method. In addition, the modified DMTS model provides quantitative information of mechanism partitioning, insinuating the failure mode via intragranular/intergranular deformation. Therefore, it has advantages over the empirical models in providing physical insights of creep failure, which can be useful to material design for performance optimization.

更新日期：2019-12-18
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-17
R. Schneider, R. J. Grant, J. M. Schlosser, W. Rimkus, K. Radlmayr, F. Grabner, Ch. Maier

Sheet metal aluminum alloys in the 5000 and 6000 series show increased formability if deformed at sub-zero temperatures which is beneficial for processing industries using sheet metals where evermore highly complex-shaped components are produced. In order to evaluate a cryogenic forming process, the temperature-dependent forming limits of the selected materials need to be known. For this determination, a device has been developed which allows deep drawing operations with circular specimens at cryogenic temperatures. The limiting drawing ratio (LDR) of the commercial aluminum alloys EN AW-5182 and EN AW-6016 are investigated in a temperature range from 298 K to 77 K. It is shown that the deep drawing behavior of both materials is generally enhanced at very low temperatures, although the LDR of the EN AW-6016 alloy increases only at temperatures T ≤ 77 K. Furthermore, using mathematical formulations and numerical (finite element) simulations the influence of friction on the punch forces could be predicted. The calculated results and experimental data are compared, and then subsequently discussed.

更新日期：2019-12-18
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-17
Paul S. Follansbee

Observations and analyses of dynamic strain aging in several metals are revisited. Common experimental trends are reviewed. A model of transport of solutes to a dislocation core is presented and predictions of the model are compared to experimental observations. A key element of the analysis is the influence of strain aging on the rate of structure evolution. The evidence presented here, based on strain-rate change measurements performed by Mulford and Kocks in Inconel 600, is that indeed the predominant effect of strain aging is to influence the rate of structure evolution. Estimates are presented for the rate of structure evolution and the extent of transport of solutes to the dislocation core in Inconel 600. While intriguing trends in hardening are observed, no fundamental insight is presented for the mechanism that contributes to the increased rate of structure evolution during strain aging.

更新日期：2019-12-18
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-17
Jian Zhao, Zhanqiang Liu, Luanxia Chen, Yang Hua

Ultrasonic energy can promote the dislocation motion in ultrasonic-assisted machining. The phase redistribution of Ti-6Al-4V alloy will occur in ultrasonic-assisted machining with appropriate ultrasonic powers. The variations of the volume fractions of β-Ti and α-Ti influence the microhardness on the processed surface. In the present paper, various rotary ultrasonic roller burnishing experiments were conducted to investigate the ultrasonic-induced phase redistribution of Ti-6Al-4V at different ultrasonic powers. The volume fractions of β-Ti and α-Ti were measured by X-ray diffraction. SEM images of the processed surfaces were used to analyze the microstructure evolution and grain refinement of Ti-6Al-4V at various ultrasonic powers. Then, the distributions of local misorientation, texture and grain boundary were observed by EBSD. The results indicated that the microhardness approached the maximum value on the processed surface while the volume fraction of β-Ti reached its maximum value. Finally, the modified phenomenological model was applied to elucidate the relationship among the microhardness, the phase volume fractions and the grain refinement. The fitting degree for microhardness between the modified phenomenological model prediction and experimental measurement was 92.2 pct.

更新日期：2019-12-18
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-13
J. Hiscocks, M. R. Daymond, B. J. Diak, A. P. Gerlich

Low-angle synchrotron transmission diffraction has been used to create high-resolution 2D residual strain maps of friction stir welds made with three processing conditions. These spatial maps of residual strain reveal local concentrations not detectable by line scans, and confirm that the asymmetric material flow known to produce asymmetric temperature and texture distributions also results in asymmetric residual strain distributions. The experimental set-up permitted simultaneous measurement of both texture and strain, which provides strong evidence against the correlation of these features in magnesium friction stir welds. Mapping diffraction peak width across the weld provides insight into the spatial distribution of dislocations and microstrains, and indicates locations of interest for higher resolution research such as TEM. A diffraction method is presented to determine the solute content of a ternary system using the lower symmetry of a non-cubic system, which can be extended to detecting the onset of precipitation among other applications. Comparison of three friction stir-welding conditions shows how the residual strains at the interface can reverse from compressive to tensile with decrease in the heat input, explaining a significant disparity in the literature results. Lower residual stress values were found to be well-correlated with improved transverse tensile behavior.

更新日期：2019-12-17
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-13
Jae-Hoon Nam, Jeongho Han, Young-Kook Lee

The effects of process temperatures for warm stamping, such as annealing (Tann), austenitizing (Taus), and stamping temperatures (Ts), on the tensile properties of Nb-bearing medium-Mn (5.9 wt pct) steel were investigated. The cold-rolled tensile specimens were first annealed at 650 °C to 750 °C, austenitized at 650 °C to 900 °C, held at Ts (500 °C to 700 °C), and then air-cooled to room temperature. Of the three process temperatures, only Taus significantly influenced the tensile properties of medium-Mn steel; in the Taus range of 650 °C to 900 °C, the amount of variation in yield strength (YS), ultimate tensile strength (UTS), and total elongation (TE) were 555 MPa, 570 MPa, and 20 pct, respectively. Particularly, when the specimens were austenitized at 730 °C to 790 °C, high YS (1060 to 1100 MPa), UTS (1760 to 1795 MPa), and TE (10.0 to 11.7 pct) were obtained due to fine-grained martensite embedded with nano-sized Nb carbides. The Nb-bearing medium-Mn specimen was successfully warm-stamped into a T-part of a B-pillar prototype at 600 °C without any cracks after austenitized at 750 °C for 5 minutes, and then air-cooled to room temperature. The warm-stamped Nb-bearing medium-Mn steel revealed the higher TE (~ 9.3 pct) than the hot-stamped 30MnB5 steel (5.3 pct) at the similar level of UTS (1855 to 1900 MPa).

更新日期：2019-12-17
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-12

Aluminum is the key ingredient in low-density steels. It leads to the formation of δ-ferrite in a large fraction. In order to study the influence, two different experimental approaches were devised. In a first of its kind, the sample was arc melted in an argon atmosphere. Later, the same alloy composition was ball milled and sintered at 1000 °C by avoiding liquid to δ-ferrite in the system. In the current study, the comparative analysis led by DICTRA simulation indicates that kappa (κ) carbide has difficulty forming in the present alloy system when δ-ferrite is already available, particularly during solidification casting.

更新日期：2019-12-13
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-11

Joining delicate electronic components for high-temperature applications is challenging. Regular soldering with lead-free or lead-based materials is typically not suitable for high-temperature applications due to their low melting points. Using off-eutectic compounds for joints offer an easy and gentle process creating joints that can be formed at a lower process temperature than the final operation temperature. Microstructural evolution near the eutectic melting point is key to be able to form reliable joints. A layered Au/eutectic Au-Ge/Au structure was used to form Au-rich off-eutectic Au-Ge joints. Columnar-like structures of primary $$\alpha$$-phase (Au) protruded through a Ge-rich off-eutectic Au-Ge mixture at the center of the joint. These structures connect the joined pieces with a single solid phase with a melting point of ca. 1064 °C. The microstructure coarsened when exposed to temperatures between 300 °C and 380 °C, i.e., near the eutectic melting point at 361 °C. Ge diffused and accumulated along grain boundaries between Au grains. Annealing above the eutectic melting point, Ge rapidly diffused and formed larger colonies of pure Ge surrounded by a Au matrix. This accords well with our previously published results demonstrating shear strength capacity of similar joints at temperatures well above the eutectic temperature.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-11
A. Goyal, V. Doquet, A. Pouya

The viscoplastic behavior of coarse and bimodal fine/ultrafine grained (F/UFG) Al5083 alloy was investigated between 20 °C and 200 °C through tensile tests at various strain rates, and stress relaxation tests to deduce the strain rate sensitivity (SRS). The plastic strain fields were measured by correlation of SEM images. In the F/UFG material at high temperature, very high strains were measured in shear bands which sometimes crossed the whole gage width and exhibited intensive grain boundary sliding (GBS). Both the SRS and ductility rose with the temperature, and as the strain rate decreased, mainly due to a rising contribution of GBS, which accommodated a much larger fraction of the global strain in the F/UFG material. The boundary between the temperature–strain rate domains where grain refinement led either to strengthening or to softening was determined. Finite element simulations of tension and relaxation tests with viscoplastic grains and sliding grain boundaries captured the macro-scale behavior of the F/UFG material. It also provided some insight into the mechanisms of correlated and cooperative GBS and grain rotation along percolation paths (both inter and intragranular), probably, responsible for macro shear banding.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-09
C. M. Fang, Z. Fan

Magnesia (MgO) particles inevitably exist in liquid Mg and may be used as potential sites for heterogeneous nucleation to achieve effective grain refinement. Understanding of the atomic configurations on MgO surfaces and in the liquid Mg adjacent to the liquid Mg/MgO interfaces is therefore of both scientific and practical interests. We investigate the surface structures of MgO in liquid Mg and the atomic arrangements of liquid Mg adjacent to liquid/substrate interfaces, using an ab initio molecular dynamics (MD) simulation technique. We find that an atomically rough terminating Mg layer forms on the {1 1 1} terminated MgO substrate (octahedral MgO) in liquid Mg. The simulations also reveal that on the structurally flat {0 0 1} terminated MgO substrate (cubic MgO) a rough Mg layer forms due to the unique chemical interactions between the ions on the substrate and the liquid metals. The surface roughness together with the large lattice misfits with solid Mg makes both octahedral and cubic MgO substrates impotent for heterogeneous nucleation of α-Mg. The present results may shed new light on grain refinement of Mg-alloys.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-09
Yuanyuan Miao, Dalei Zhang, Ning Cao, Liuyang Yang, Hong Ju, Rabah Boukherroub, Xueqiang Lin, Huiping Li, Youhai Jin

Inspired by mussel adhesive protein, the uniform, compact, and superhydrophobic film was constructed on the 316L stainless steel (316L SS) using self-polymerization of dopamine (DA) and further functionalization of the resulting polydopamine film with 1H,1H,2H,2H-perfluorodecanethiol (PFDT) to form a thin fluorinated polydopamine (fPDA) coating. Electrochemical analysis revealed that the superhydrophobic fPDA coating has an outstanding potential, lower corrosion current density, and higher coating resistance to protect 316L SS against corrosion in a 3 wt pct NaCl environment. Characterization of the corrosion attack by scanning vibrating electrode technology (SVET) reveals the cooperative effects of superhydrophobicity and strong adhesive ability of the fPDA coating on the highly anticorrosion capability of 316L SS in a 3 wt pct NaCl aqueous solution.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-09
Xuefeng Zhou, Zhixia Zheng, Weichao Zhang, Feng Fang, Yiyou Tu, Jianqing Jiang

Deformation-induced carbide transformation (DICT) is first observed in M2 high-speed steel (HSS) wherein deformation enables a lower transformation temperature and enhanced transformation rate of M2C carbide into M6C and MC. Dislocations introduced into M2C by pre-deformation act as nucleation sites of new precipitates and enable an evolution of the transformation pathway from a common interface-nucleation mode to a dislocation-nucleation manner. DICT offers an opportunity to circumvent the carbide-related trade-off between the wear resistance and toughness of M2 HSS.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-09
Hailiang Huang, Guoquan Liu, Hao Wang, Asad Ullah, Benfu Hu

The dissolution behavior and kinetics of γ′ precipitates during solution treatment were investigated in an advanced powder metallurgy nickel-based superalloy FGH98. The microstructural evolutions were quantitatively characterized, and the dissolution kinetics were evaluated. The results show that due to the influence of precipitate size and element distribution, the dissolution rate of secondary γ′ precipitates was higher than that of large primary γ′ precipitates, but lower than that of small tertiary γ′ precipitates. With the increase of holding time, the area fractions of γ′ precipitates decreased and then gradually approached a thermodynamic equilibrium for all three heating temperatures. The dissolution kinetics of γ′ precipitates were quantitatively evaluated using the JMAK model. During the initial stage, the dissolution rate decreased rapidly with increasing holding time, and then, changed more slowly. The dissolution activation energy of γ′ precipitates increased with increasing holding time.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-09
Suwaree Chankitmunkong, Dmitry G. Eskin, Chaowalit Limmaneevichitr

Piston Al-Si alloys have very complex compositions and multi-phase heterogeneous structure, so it is necessary to control the formation of primary and eutectic compounds. In this study, the ultrasonic melt processing (USP) of a eutectic Al-Si piston alloy (AA4032-type) was performed in a permanent mold and during direct-chill (DC) casting to study its effects on the structure refinement and modification. The principal difference between these two ways of casting is that in the permanent mold the solidification front progressively moves towards the ultrasound source, while in the DC casting the position of the solidification front is fixed in space. The results showed that the USP can successfully refine primary Si, Fe-containing intermetallics and aluminum grains. Refinement of primary Si was accompanied by the increase in its amount, which was attributed to both enhanced heterogeneous nucleation and fragmentation. The refinement of Fe-containing intermetallics and Al grains resulted from the fragmentation mechanism and were more pronounced when USP was applied below the liquidus temperature in the permanent mold. However, the eutectic phases coarsened upon USP, and this effect was most pronounced when USP was applied to the semi-solid material. This was related to the strong attenuation of acoustic waves, which effectively heats the semi-solid material and induces corresponding coarsening of the phases. Acoustic streaming induced by an oscillating sonotrode affected the depth of the sump while simultaneously decreasing the macrosegregation, which reflects the dominant role of the melt flow directed against natural convection. The results demonstrated the importance of the solidification stage at which the USP was applied and the specifics of the USP mechanisms acting at the different stages of solidification.

更新日期：2019-12-11
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
Zhenfeng Xu, Zhimin Ding, Bo Liang

In the original article there is an error in institution’s name for the affiliation of Zhenfeng Xu and Zhimin Ding. The correct institution is Dalian Jiaotong University.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
M. Enomoto, K. Hayashi

The nucleation and growth of austenite during continuous heating in plain carbon martensite is simulated using classical nucleation and diffusion growth theories assuming that austenite is nucleated on cementite particles at prior austenite grain boundaries and martensite packet, block, and interlath boundaries. A critical nucleus model on the spherical substrate was modified to take into account the influence of the boundary energy on which cementite particles formed. Simulations were carried out using the particle size distribution of cementite measured in an Fe-0.2 mass pct C alloy heated to near eutectoid temperature (Ae1). Austenite nucleation stopped in a very short time regardless of boundary site or particle size of cementite due to the fast decrease in carbon supersaturation and the depletion of nucleation sites. The fraction of austenite nucleated on cementite at prior austenite boundaries and martensite packet boundaries etc was much greater than that nucleated on cementite at interlath boundaries. While cementite particles dissolved quickly after austenite was nucleated, a large proportion of cementite particles at lath boundaries remained undissolved until they disappeared at 30 °C to 40 °C above Ae1. The evolution of austenite grain size was also simulated after austenitization was completed, and compared with experiment.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
Xiaojun Zhao, Zhiqiao Li, Houwen Chen, Rainer Schmid-Fetzer, Jian-Feng Nie

The equilibrium intermetallic phase in Mg-Nd-Ag alloys has not been well understood. In this work, intermetallic particles in the solution-treated microstructure of commercial magnesium alloy QE22 (Mg-2.5Ag-2.0Nd-0.7Zr, wt pct) have been investigated using scanning electron microscopy, electron diffraction, atomic-resolution imaging and mapping techniques of scanning transmission electron microscopy (STEM) and thermodynamic modelling. The intermetallic particles are distributed in the inter-dendritic regions. They have coarse irregular shape and share the same crystal structure. The intermetallic phase (designated δ) is determined to have an orthorhombic structure (space group Cmcm, a = 1.02 nm, b = 1.18 nm, c = 1.00 nm) and a composition of NdAgMg11, which are different from those reported previously. An atomic model is proposed for the δ phase based on atomic-resolution STEM images and atomic-scale energy-dispersive X-ray spectroscopy maps. The δ lattice is structurally related to that of Mg12Nd phase in binary Mg-Nd alloys. The Gibbs energy of formation of NdAgMg11 is determined from the equilibrium study at 793 K (520 °C), including the entropy of formation using the present experimental phase analysis data obtained at lower temperature. Implications to the formation temperature range and thermal stability of this phase and alloy solidification are discussed based on the calculated Mg-Nd-Ag phase diagram and Scheil solidification paths of alloys.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
Olga Tsurtsumia, Fernando Pedraza, Benjamin Gregoire, Nugzar Khidasheli, Elguja Kutelia

This work reports on the aluminization and oxidation behaviour of a new class of cast iron (deformable austempered ductile iron, DADI). The slurry aluminization resulted in uneven coatings due to the lack of wettability of molten aluminium to the graphite inclusions of the substrate. In spite of this, the isothermal tests at 650 °C for 100 hour in air revealed a drastic reduction of oxygen uptake related to the formation of mixed Al-containing spinels compared to the very unprotective iron oxides formed in the absence of coating. It derives that deposition of thicker aluminide layers by precoating with, e.g. nickel would be a promising way to protect further DADI cast iron.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
Sung Bo Lee, Jinwook Jung, Seung Jo Yoo, Heung Nam Han

To date, much research has been conducted into the effect of migration pinning on the grain size in polycrystalline materials. However, effects of migration pinning on the grain-boundary structure and its transition have not been illuminated. Here, using transmission electron microscopy (TEM) we have explored the pinning effects for the grain boundary in a Ni bicrystal. During TEM specimen preparation, a hole was intentionally drilled in the middle of the grain boundary as a pinning point against grain-boundary migration. The specimen was heated to 600 °C. The grain boundary is driven to migrate by both the surface energy anisotropy and the total strain energy reduction. Grain-boundary facets with a plane orientation of {0 3 2}//{1 1 1} appear near the hole. The facets undergo a structural transition from atomically flat to rough with increasing distance from the hole. A pinning force exerted by the hole suppresses the migration of the grain boundary near the hole, indicating that the grain-boundary region away from the hole is subjected to a higher driving force. It certainly appears that the phenomenon originates from a change in driving force with the distance from the hole, being a signature of kinetic roughening.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
Ali Günen

Silicide-free boride layers were grown on Inconel 718 Ni-based superalloy surface at 850 °C, 950 °C, and 1050 °C for 2, 4, 6 hour by the powder pack-boronizing process using nano-sized B4C powders. The coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 3D profilometry, and microhardness measurements. Wear experiments were carried out on untreated and boronized Inconel 718 using a ball-on-disk tribometer under dry sliding conditions at temperatures of 25 °C, 400 °C, and 750 °C. An increase in boronizing temperature and duration increased the thickness and hardness of the obtained boride layers, which resulted in low coefficient of friction values and decreased wear rates. Scanning electron microscopy images of the worn surfaces revealed two-body abrasion as the effective wear mechanism in the untreated samples, and three-body abrasion assisted by microcracking and spalling as the dominant wear mechanism in the boronized samples. A transition from mild to severe wear occurred in the untreated samples, while wear rates remained low in the boronized samples up to 750 °C. In conclusion, boronized Inconel 718 was capable of sustaining its boride layers under 5 N for 1800 m at wear-test temperatures up to 750 °C.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-06
E. E. Wright, M. J. Kaufman, G. R. Weber

The localized deformation behavior during tensile straining (0 to 9 pct) and its effect on the corrosion properties of two third-generation Al-Li alloys (2099 and 2196) were investigated. Both electron backscatter diffraction and 2D micro-digital image correlation were used to examine site-specific effects of orientation and microstrain evolution during tensile straining. After straining, in situ tapping mode atomic force microscopy was used to study galvanic corrosion as it occurred in artificial seawater (3.5 pct NaCl). Regions of high microstrain corroded preferentially, and large, recrystallized grains in mostly unrecrystallized microstructures were highly detrimental to corrosion properties. Recommendations for improved thermomechanical processing and/or alloying to promote corrosion resistance of 2XXX series Al-Li alloys were considered.

更新日期：2019-12-07
• Metall. Mater. Trans. A. (IF 1.985) Pub Date : 2019-12-04