查看更多>>摘要：The crystal structure, magnetic phase transition and magnetocaloric effect in R5CoSb2 (R = Pr, Nd, Gd-Er) alloys are investigated. All alloys are crystallized in the Yb5Sb3-type orthorhombic structure. R5CoSb2 (R = Pr, Nd, Gd-Er) alloys undergo ferromagnetic (FM)-paramagnetic (PM) transition under 1 T. The magnetic phase transition of the R5CoSb2 (Gd-Er) alloys is of second-order nature, whereas the first-order phase transition takes place in the R5CoSb2 (R = Pr and Nd) alloys at a low temperature. For delta mu H-0 of 0-5 T, the values of the maximum of entropy change (the relative cooling power) are 6.4 J/kgK (97.8 J/kg), 2.2 J/kgK (108.7 J/kg), 7.5 J/kgK (592.5 J/kg), 5.2 J/kgK (400.4 J/kg), 6.2 J/kgK (413.5 J/kg), 9.0 J/kgK (423.0 J/kg) and 10.4 J/kgK (299.5 J/ kg) in R5CoSb2 (R = Pr, Nd, Gd-Er) alloys near the phase transition temperature.
查看更多>>摘要：The aim of this work is to investigate the compression deformation behavior of the Nb-Si based alloy with an Al-Y modified silicide coating at different conditions, including the height reduction, deformation temperature, strain rate and oxidation. The results showed that the silicide coating and substrate have a good coordinated deformation at a higher temperature or at a lower strain rate. While at a lower deformation temperature (1100 degrees C, 1200 degrees C) or a higher strain rate (0.005 s-1), the silicide coating shows a barrier effect on the deformation of substrate. At 1350 degrees C, the grains of NbSi2 phase in the coating were coarsened significantly. During the high temperature compression process, the coating can undergo a certain degree of plastic deformation, and NbSi2 phase in the coating would form sub-grain and a small amount of recrystallized grains. The crack initiation and propagation in the coating and substrate during compression deformation have also been discussed. The big cracks produced in the process of oxidation can be pressed gradually with the increase of the height reduction. The oxidation of the coating has no significant effect on the compressive properties of the alloy.
查看更多>>摘要：Single-crystal Cu can be potentially applied as pad or micro bump in bonding technology for advanced packaging. A novel bonding method with an extra temperature gradient (TG, TG-bonding) was carried out to bonding single-crystal (111)Cu and poly-crystal Ni substrates with Sn as interlayer. The morphology and orientation evolution, elemental distribution and growth kinetics of interfacial (Cu,Ni)6Sn5 intermetallic compound (IMC) in (111)Cu/Sn/Ni micro joints during isothermal and TG-bonding were investigated. Regular roof-type (Cu,Ni)6Sn5 grains along three intersectant directions with an angle of 60 degrees formed at the initial Sn/(111)Cu interface and maintained the roof-type morphology with (1120) preferred orientation throughout the isothermal bonding. For TG-bonding, TG-induced atomic thermomigration (TM) and Cu-Ni cross-interaction co-played a critical role in the morphology, grain feature and growth kinetics of the interfacial IMCs. Moreover, rapid growth of (Cu,Ni)6Sn5 phase was achieved by TG-bonding with (111)Cu as hot end to fabricate full IMC joints which had higher shear strength than the cases of isothermal and TG-bonding with (111)Cu as cold end. The proposed method would provide a further insight for developing bonding technology for advanced packaging.
查看更多>>摘要：The distributions of tungsten (W) in Ni-based single crystal superalloys with different Re and Ta contents are characterized and specified by atom probe tomography. The results show that Ta changes the partitioning behavior of W and rejects it from the gamma '-precipitate to the gamma-matrix, while Re shows the opposite effect, which is consistent with the simulations via Thermo-Calc. Moreover, significant behaviors of W segregation at gamma/gamma ' interface are found in 2Ta2Re, 5Ta2Re, and 5Ta0Re alloys, contributing to the decrease in the interfacial energy. W interfacial segregations are conducive to decrease the interfacial energy. By comparing alloys with different W contents, W segregation is irrelevant to the W content, but highly W-partitioning-dependent. Additionally, nanoindentation tests also show that the addition of Re can significantly increase the hardness of gamma-matrix, while Ta is conducive to strengthen within both gamma-matrix as well as gamma '-precipitates which is clarified by the solid solution strengthening calculations.
查看更多>>摘要：Porous CoAl3 is a candidate material in the field of catalytic due to its high porosity, good thermostability and quasicrystal structure. However, its rapid preparation are still a challenge, and the oxidation resistance need to be further investigated. In this work, we have rapidly prepared porous CoAl3 by thermal explosion (TE) reaction and studied its oxidation process. The results show that two exothermic peaks at 616 C and 646 C, corresponding to the solid-phase diffusion and TE reaction, respectively. The heat released from the two reactions led to the expansion of the compact, which reached a maximum of 104% at 800 C, and the corresponding open porosity reached at 53%. The pore sources include the original pores during the green compact pressing process, the Kirkendall pores generated by the solid-phase diffusion process and the in-situ pores generated by the Al consumption after the TE occurs. The cyclic oxidation of porous CoAl3 at 700 C for 130 h only increased the weight by 1.52%, forming a continuous protective oxide film on the surface of the skeleton. It has been found that porous CoAl3 can combine the oxidation resistance of Co-Al monoliths alloys and the high porosity of porous materials, which have potential applications in the field of catalysis such as methanation at 600-700 C.
查看更多>>摘要：In this paper, the recrystallization mechanism of alpha phase, microstructure evolution and tensile fracture behavior of in-situ (TiBw + TiCp)/near-alpha titanium matrix composites have been investigated. The subgrain boundaries formation within alpha(p) was caused by strong recovery. The reinforcements played an important role in the recrystallization of alpha phase. Therefore, the continuous dynamic recrystallization, reinforcements stimulated recrystallization and static recrystallization have a common effect on the alpha(p) recrystallization. The room temperature ductility was dominated by the size of silicides, slip transmission between alpha(p) and alpha/beta colony, and the morphology of microstructure. The large-scale silicide caused the reduction of ductility at room temperature. After annealed at 1040 C, the ultimate tensile strength and yield strength at 650 C of the composites was 745 MPa and 620 MPa, respectively, and the yield strength at 700 C reached 530 MPa, which has a balance between strength and ductility. The fracture of the composites was associated with the dislocation migration hindered by the boundaries or interaction with each other and the slip of boundaries. Therefore, pores will nucleate in this region due to stress concentration, and the eventual failure were mainly caused by the propagation and connection of pores to big cracks. The above superior performances make the titanium matrix composites have a great application prospect in aerospace fields.
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Elsevier