查看更多>>摘要：A comparative study of high-entropy metallic glasses and their reference counterparts was conducted via mechanical relaxation behavior and high-temperature deformation. We show that the high-entropy metallic glasses possess a relatively more homogeneous structure, which generates smaller activation volumes and sluggish free volume evolution during high-temperature deformation. A spectrum analysis that allows to delineate the deformation details of high-entropy metallic glasses were constructed. The core finding sheds important light on the structural heterogeneity and sluggish dynamics and provides an essential piece for understanding the deformation mechanism of high-entropy metallic glasses.
查看更多>>摘要：Experimental results show that voids inside additive manufactured (i.e. 3D printed) materials are unavoidable. As such samples are often post-printing annealed, it is thus of interest to understand how voids affect boundary migration. In this work, phase field simulations of recrystallization are carried out for systems containing voids and typical inhomogeneous microstructures. The simulation results show that the voids significantly affect the shape of the boundary and its migration kinetics during recrystallization. The location of the voids in relation to the inhomogeneous deformation microstructure is furthermore found to affect local boundary migration. The results are not only of importance for optimizing annealing of printed samples, but also for understanding local boundary migration in particle containing alloys.
Kim, Ga-YeongKim, Tae-HoonCha, Hee-RyoungLee, Sang-hyub...
6页
查看更多>>摘要：We report a method to produce high-performance and cost-effective Ce-substituted Nd-Fe-B hot-deformed magnets with 30% Nd reduction. To suppress the formation of the Ce-dissolved REFe2 phase, which primarily limits [001] texture development and RE-rich grain boundary phase formation, amorphous melt-spun precursors were used to fabricate 30%-Ce-substituted hot-deformed magnets. By suppressing the formation of REFe2 phase from the precursors, the c-axis alignment of 2:14:1 platelets in the magnets due to grain boundary sliding and rotation improved, and the Nd/Ce-concentration of grain boundary phases in the magnets increased. As a result, both coercivity (Hcj) and remanence (4 pi M-r) of the magnets noticeably increased to 15 kOe and 13 kG, respectively, in relation to those of the magnets fabricated from crystalline precursors containing an REFe2 phase (H-cj = 13.4 kOe, 4 pi Mr = 12.1 kG). The magnetic performance of the 30%-Ce-substituted magnets developed in this work is sufficient to replace the N42M-graded commercial Ce-free magnets.
查看更多>>摘要：Three-dimensional orientation mapping in the transmission electron microscope (3D-OMiTEM) has been used to characterize the grain structure of an ion-sputtered gold nanoparticle film. The three-dimensional morphology and crystallographic orientations of ~7500 grains in more than 1200 nanoparticles were reconstructed. It was found that the grains have an average size of 8 nm and a weak crystallographic texture. A five-parameter grain boundary character analysis revealed that the microstructure mainly consists of sigma 3, sigma 9, sigma 11, and sigma 27a boundaries. Differences in the grain boundary plane distributions for these specific misorientations compared to those found for coarse grain-size materials were attributed to extensive grain boundary termination at nano particle surfaces. The grain boundary population is, nevertheless, on average inversely correlated to the grain boundary energy, as reported in previous studies. These findings can serve as a guide for tailoring the grain boundary character distribution and properties of nanoparticles and nanocrystalline thin films.
查看更多>>摘要：Here, a new strategy, i.e., laser shock peening (LSP) followed by cyclic deep cryogenic treatment (DCT), is proposed to generate the gradient hierarchical structures and thus promote strength-ductility synergy of a high entropy alloy (HEA). We show that the non-equiatomic CrFeCoNiMn0.75Cu0.25 HEA sample treated by this new strategy possesses an excellent combination of high strength (~1100 MPa) and high plasticity (30%). Higher yield strength is achieved in HEA samples treated by LSP, due to the introduction of a gradient microstructure comprising sub-grains, dense dislocations and nano-twins (NTs) near the treated surface. Then, the following cyclic DCT processing can further introduce various types of reinforcing defect microstructures in core region of LSP-treated HEA, including dense intersecting NTs and stacking faults, thus effectively improving the tensile strength and plasticity. These results obtained here can shed new insights into develop high performance HEAs by tailoring residual stress and generating optimized microstructures.
查看更多>>摘要：A sharp difference was revealed between strengthening retention of the Al-Al3Ni eutectic at temperatures up to 500 & nbsp;C and room-temperature strengthening recovery after high-temperature exposures. Although the Al3Ni fibers exhibited high coarsening resistance that led to a remarkable recovery of about 80% of the eutectic yield stress after 1 week exposure at 500 & nbsp;C, they were ineffective in retaining the strength at high temperatures that at 500 & nbsp;C reached only 20% of the room-temperature level; the same retention ratio as for the identically-deformed pure aluminum that resembled the eutectic composite matrix. During uniaxial compression at 400-500 C, the steady-state flow stress with negligible work hardening rate developed for both the eutectic and pure aluminum. The Al3Ni fibers did not act as potent nuclei towards promoting the dynamic recrystallization, resulting in dynamic recovery being the only microstructure restoration mechanism during hot deformation.
查看更多>>摘要：The mismatch of thermal expansion in Mg and Al/Cu alloys may cause flaking or destruction at a joint interface, and further restrict their service life and practical application. Combining the negative thermal expansion materials could reduce the thermal expansion of Mg alloys, but destroy their ductility. In this study, we overcome this challenge by the combination of MnCoGe-based alloys with Mg-9Al-1 Zn Mg alloys. The addition of less than 7 wt% Mn0.98CoGe has shown matched coefficient of thermal expansion of Cu alloys, and moderated strength and plasticity. Due to the inconsistency with the predicted values, we figured out the critical mechanism on both thermal expansion regulation and mechanical property improvement is attributed to the secondary phases and the metallic bonding interfaces. These Mg alloys with low thermal expansion and good mechanical properties could be useful to the electronic packaging and precision fields.
查看更多>>摘要：Thin film metallic glasses (MGs) are promising materials for electronic applications. While the transport prop-erties of MGs are composition dependent, the influence of hybridization on the resistivity has not been inves-tigated systematically. We implement a correlative experimental and computational approach utilizing thin film deposition, electrical resistivity measurements, synchrotron X-ray diffraction and ab initio calculations to explore the relationship between the fraction of hybridized bonds present in PdAlY-M glasses with M=Ir,Au,Ni, where the electrical behavior is dominated by d-electrons. The strong bonds hybridization in PdAlY-Ir yields a high resistivity of 175 mu omega m, while the weakly hybridized bonds in PdAlY-M MGs (M = Au, Ni) result in lower re-sistivities of 114 and 92 mu omega m, respectively. We propose that an increase in the amount of anti-bonding states close to the Fermi level yields an increased room temperature resistivity.
查看更多>>摘要：Synchrotron X-ray analysis of the Sn electromigration behavior and Sn whisker growth in a Blech structure using nano-X-ray fluorescence microscopy and white beam Laue nanodiffraction was conducted. Sn depletion at the cathode and whisker/extrusion formation at the anode were characterized in-situ, and the results obeyed the electromigration kinetics. This electromigration scenario gradually decayed because of the counterbalance between electron wind force and back stress. White beam Laue nanodiffraction analysis showed that a noticeable compressive deviatoric stress in the direction of electron flow built up at the anode of Sn strips, particularly in the roots of Sn whiskers, confirming that electromigration-induced atomic accumulation occurred downstream in a strip and that Sn whiskering was closely related to internal stress resulting from atomic accumulation in confined segments. Finally, a theoretical model based on fundamental electromigration theory revealed that Sn diffused predominately through lattice and grain boundary paths at Sn homologous temperature of 0.6.
Mogeritsch, JohannRettenmayr, MarkusLudwig, Andreas
6页
查看更多>>摘要：Understanding phenomena that occur during gradient annealing and initial transient of Bridgman-type directional solidification processes is essential for producing high-performance materials with specific properties. An experiment with alternating long time gradient annealing and directional solidification periods was performed on the International Space Station, using a near-peritectic transparent TRIS-NPG alloy. It transpired that accumulation of solute ahead of the solid/liquid interface continued to progress and that steady-state growth conditions were never achieved. The results demonstrate that (i) liquid being squeezed out from the mush during the long time gradient annealing period disables the formation of a flat interface; (ii) a thermal bias caused a slightly tilted planar solidification front; and (iii) growth of the metastable pro-peritectic alpha-phase led to the formation of a supersaturated solid that solidified with an intriguing low growth rate.
NSTL
Elsevier