查看更多>>摘要：The addition of trace (TiB + TiC) reinforcements could minimize the deformation steps and decreases its costs according to recent study. In present work, the hot deformation behavior and microstructure evolution were studied via the isothermal hot compression at different temperature and strain rate. Based on the DMM model, the activation energy Q and processing map were obtained. Subsequently, two billets were hot-rolled and heat-treated, to study the microstructure and tensile properties of the alloy. Results revealed that the fow behavior of the (TiB + TiC)/Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe alloy was similar with other near β titanium alloy. When deformation in β region, the deformation mechanism was associated with cDRX by lattice rotation and dynamic recovery; when deformation in (α + β) region, the deformation mechanism was associated with substructure evolution, such as DRX and dynamic recovery. The lower strain rate guarantees abundant time for microstructure transformation, while the higher strain rate leads local fow instability and cracks. The activation energies Q is 264.1 kJ/mol in (α + β region and 181.8 kJ/mol in the β region. According to the processing map, the optimum deformation windows are 770-800℃ and 850-880℃, 0.001 s1. In addition, the microstructure of 770R + SAT is characteristic of duplex microstructure with a certain amount of α_p, considerable precipitation of fne acicular α_s and continuous (Xgb, which is achieved a UTS of 1414 MPa with a poor ductility. Therefore, the (TiB + TiC)/ Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe alloy shows excellent deformability and higher strength, which is possible to achieve both high economy (less deformation step) and advancement (high mechanical properties due (TiB + TiC) reinforcements).
查看更多>>摘要：An X-ray tomography setup is developed in this work in order to characterize liquid metal embrittlement (LME) cracks and internal defects in 3D in homogeneous advanced high strength steel resistance spot welds, non destructively. For the frst time, the propagation of the LME inner crack could be monitored in the course of ex situ tensile shear loading. While propagating in a stable way through the sheet thickness in the vicinity of the weld nugget, the LME inner crack does not modify the fnal fracture path, all investigated welds failing at the faying surface (full interfacial failure type).
查看更多>>摘要：In this study, implantable Al_2O_3/Ti-13Nb-13Zr (TNZ) alloy joints were achieved by diffusion bonding. The effects of bonding temperature and holding time on interfacial microstructure and mechanical properties were investigated. The interfacial microstructures of the joints bonded at various temperatures and holding time were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The typical microstructure of the Al_2O_3/TNZ joint, which was obtained at 1175 ℃ for 60 min under a pressure of 3 MPa, was Al_2O_3 ceramic/TiAl layer + TiO_2 + Nb_2O_5 + AlNb2/continuous Ti3Al layer/acicular Ti3Al + Ti (s,s)/TNZ substrate. The presence of Ti element mainly contributed to the metallurgical bonding between TNZ and Al_2O_3 ceramic. Nb reacted with Al_2O_3 ceramic forming Nb_2O_5 and AlNb2 phases which played important roles in interfacial bonding. With the increase of bonding temperature or holding time, TiAl layer and Ti3Al layer thickened gradually while the number of Nb_2O_5 and AlNb2 frst increased and then decreased. This corresponded to the change of average shear strength of these joints, which initially rose and then declined. The maximum of average shear strength reached 52.0 MPa when joints bonded at 1175 ℃ for 60 min under a pressure of 3 MPa, and the bonded joints mainly fractured at Al_2O_3 ceramic.
查看更多>>摘要：The transient thermal shock and helium ion irradiation damage behaviors of oxide dispersion-strengthened tungsten (ODS-W)/CuCrZr alloy joints prepared by direct diffusion bonding and by improved diffusion bonding via surface nano-activation and Cu electroplating were studied. The surface morphologies and interface structures of the ODS-W/CuCrZr joints after thermal shock and He~+ irradiation were investigated by atomic force microscopy, scanning electron microscopy, focused ion beam/scanning electron microscopy, and high-resolution transmission electron microscopy. The joint of ODS-W and CuCrZr prepared by the improved diffusion bonding method exhibited superior resistance to crack formation. No obvious plastic deformation was found on the ODS-W surfaces of the ODS-W/CuCrZr joints obtained by either bonding method after transient thermal shock (power density = 0.6 GW/m2). Interfacial debonding was observed to occur at the interface of W and Cu in the direct diffusion-bonded ODS-W/CuCrZr joint where Y2O3 particles exist, but did not occur in the joint prepared using the improved method. The nanostructures formed at the interface of the joint via the improved diffusion bonding method therefore elevated the radiation resistance of the joint. These results should be of relevance for the development of plasma-facing components in future nuclear fusion reactors.
查看更多>>摘要：The evolution of Cu particles which form in a Cu-bearing medium Mn steel, whose composition is Fe-0.16C-5.62Mn-2.01Cu-1.95Ni-0.65Al-0.49Si in mass%, was investigated with focus on Cu particles in the reversed austenite. Almost all Cu particles were formed in the martensite matrix during heating to annealing temperature, and calculation of phase boundaries and miscibility gaps in the multi-component alloy indicated that Cu particles in annealed martensite were probably incorporated into reversed austenite with the migration of α/γ interface during annealing. DICTRA simulation and STEM-EDX analysis revealed that the partitionless mode of austenite growth prevailed at an earlier stage and it switched to a mode accompanying alloy partitioning. Cu particles in the ferrite (or annealed martensite) matrix partially dissolved and the rest coarsened during annealing while Cu particles in austenite were on the way to total dissolution, but the rate was slow. As a result, the size and volume fraction were greater near the α/γ interface in austenite and they were opposite in the center of reversed austenite. During deformation, retained austenite provided a remarkable TRIP effect. Cu particles in the ferrite matrix caused strengthening signifcantly and those in austenite could have a function of delaying the decreasing in strength due to slow diffusivity of alloy elements and dissolution rate.
查看更多>>摘要：The present study aimed to investigate the impact of pre-deformation on the structure-deformation-property relationship in Cr-Mn-N austenitic stainless steel (ASS). The commercial Cr-Mn-N ASS was cold-rolled (CR) at room temperature with a thickness reduction from 5% to 60%, whose microstructural characteristics were identifed by optical microscopy, scanning and transmission electron microscopy, and electron backscatter diffraction together with X-ray diffraction. The results indicated that the microstructure varied from equiaxed austenite in the as-received specimen to the coexistence of stacking faults (SFs), deformation twins (DTs) and strain-induced martensite (SIM) in pre-deformed specimens. Furthermore, detailed TEM results showed that equiaxed dislocation cells, DT nets and dislocation-cell-type α'-M occurred in the 60% CR specimen. Tensile tests revealed that the strength of ASS increased while the plasticity decreased with the increase of pre-reduction deformation. Such mechanical properties were confrmed to be related to the variations in microstructure-dependent deformation mechanisms, varying from planar slip + DTs + SIM in the as-received specimen, to DTs + SIM with 30% reduction, and SIM + minor twinning with 60% reduction, respectively, in the pre-deformed specimens.
查看更多>>摘要：Pure indium (In) solder is promising as the thermal interface material (TIM) for effcient heat dissipation and as the Pb-free solder for cryogenic joining applications. In this study, liquid/solid and solid/solid reactions between In and Au/Ni(V) surface fnish on a Si chip are investigated to explore the formation of intermetallic compounds (IMCs) formed at the In/Au/Ni(V) interface and their growth kinetics. Two IMCs, (Ni,Au)28In72 and Ni-V-In, are formed at the interface in the liquid/solid and solid/solid reactions performed at 220-260 ℃ and 100-150 ℃, respectively. The growth of the (Ni,Au)28In72 crystalline phase follows the parabolic law and the underlying Ni-V-In amorphous phase is formed as a result of phase transformation from original Ni(V) due to outward diffusion of Ni and inward diffusion of In. This phase transformation proceeds at a faster rate in the liquid/solid reaction. The Ni supply is exhausted once the Ni(V) is completely transformed into the Ni-V-In phase, accelerating the ripening reaction of (Ni,Au)28In72 and its spallation into the molten In matrix.
查看更多>>摘要：This work aims to investigate the electrical sliding wear behavior of the dual-scale particulate reinforced copper matrix composites by a self-developed pin-on-disk wear tester. Cu-xCr-0.3Zr-1ZrB2 (x = 0, 0.5, 1.0) composites were fabricating by casting and cold rolling. The microstructure of worn surfaces was examined using scanning electron microscopy (SEM) and laser scanning confocal microscope to unravel the wear mechanisms. The results indicated that the combined effect of mechanical wear and electrical wear dominated the wear process with an increase in the apparent normal load. Amplifying the electrical current increased the wear loss of the sliding pair, in the meantime alleviated the fuctuation of the friction coeffcient with marginal changes in the average values. After introducing Cr element and ZrB2 particles, the wear rate decreased from 0.197 mg/m to 0.141 mg/m under moderate operating test conditions. Adhesive wear and abrasive wear occupied an important position in the wear mechanism of the Cu-1wt%Cr-0.3wt%Zr-1wt%ZrB2 composite under electrical current due to the elevation of thermal stability and the formation of a tribolayer introduced by these reinforcements.
查看更多>>摘要：Dislocation motions driven by electron-beam illumination were in-situ observed in a single-crystalline gold thin-foil specimen, under a medium-voltage transmission electron microscope operated at 200 kV. The dislocation motion characteristics were in-situ observed under the bright-feld and weak-beam dark-feld conditions. The structures formed through the dislocation motion were also characterized using bright /dark-feld imaging and high-resolution techniques. Two types of dislocation motions are concluded, where one type of motion left no apparent traces, and the other type left a clear trace of passage. The dislocation motions have jerky behaviors, and the motions are accelerated when the beam intensity is increased. The immobile trace structures left by the dislocation motions are identifed to be twin structures oriented along the 〈111〉 crystal directions. The dislocation motion mechanism is discussed and the motion might be caused by the electron beam heating effect or the electron beam induced phonon effects. The dislocation disassociation, planar defect formation in the Au crystal, and the beam heating impacts are also discussed.
查看更多>>摘要：In this study, binary Mg-2Y alloy, pure Mg, and AZ31 alloy were prepared via cold rotary swaging. Micro-structure evolution during the grain refnement process was explored using transmission electron microscopy. The results showed that it was impossible to achieve nanocrystallization in pure Mg via cold rotary swaging, which was attributed to the diffculty of forming dislocation arrays. In contrast, after swaging, nanograins were obtained in an alloy formed by adding 2 wt% Y to Mg. In the early stage of swaging, the initial coarse grains of the Mg-2Y alloy were subdivided by the formation of twin lamellae, dislocation arrays (in the matrix) and deformation bands. With increasing strain, more dislocation arrays were formed within the twin lamellae and deformation bands, which resulted in further refnement of the twin lamellae and deformation bands and promoted the formation of nanoscale subgrains. As the swaging process continued, these nanoscale subgrains transformed into nanograins with high-angle grain boundaries. Nanograins were also developed in the swaged AZ31 alloy. The formation rate of nanograins during swaging was slower, and the grain refnement effect after swaging was weaker, in the Mg-2Y alloy than the AZ31 alloy.
NSTL
Elsevier