查看更多>>摘要：? 2022 Elsevier Inc.In this work, the performance differences between rolled and selective laser melted (SLM) Ti6Al4V alloys used commonly for orthopedic implants were investigated. By rotation bending fatigue (RBF) and in-situ fatigue tests, the SN curves, crack propagation rate (da/dN) curves and cracking behavior of the SLM samples (in 0°, 45° and 90° directions) and rolled samples (fabricated along the rolling and transverse directions (RD and TD)) were compared. Slight fatigue performance distinction was identified for the rolled TD and RD Ti6Al4V samples. However, the building directions exhibited an obvious impact on the SN and da/dN curves of the SLM Ti6Al4V alloy. The SLM 45° samples revealed excellent crack propagation resistance and the fatigue limit of the SLM 0° samples reached to that of the rolled Ti6Al4V alloy. The fatigue performance difference of the SLM components in different SLM directions can be expected. Moreover, the crack aspect ratios (a/b) of the SLM Ti6Al4V alloy were obtained from sample fracture surfaces. The effect of SLM building directions on the a/b values was revealed. Based on the results, the residual fatigue lives of the SLM and rolled Ti6Al4V hip joint prostheses were compared by finite element simulation. The SLM prostheses exhibited excellent fatigue performance and could replace the existing components fabricated by traditional alloys in some fields.
查看更多>>摘要：? 2022 Elsevier Inc.This study focuses on the brazing of IC10 Ni3Al-based superalloy to (CoCrNi)94Al3Ti3 medium-entropy alloy (MEA) using a NiCrSiB filler metal. The microstructure of the brazed joint was comprehensively investigated, and the forming mechanism of the joint was elucidated. The mechanical properties and fracture behavior of the joint were evaluated. The diffusion of boron from the filler to substrates led to the diffusion-affected zone (DAZ), and the M3B2- and M5B3-type boride were precipitated with the coherence of (3 1 0)BCT//(2 0 0)FCC (M3B2) and (0 0 2)BCT//(2 0 0)FCC (M5B3) adjacent to the IC10 and MEA substrate, namely the DAZ I and II respectively. In addition, the edge dislocation reduced the mismatch between the M3B2 boride and the γ matrix. The isothermal solidification zone (ISZ) was formed near the DAZ when the liquidus temperature reached the brazing temperature due to the diffusion of boron and Si and the dissolution of substrates. The formation of ISZ was effectively activated at high brazing temperatures (1090, 1120, and 1150 °C). The athermal solidification zone (ASZ) was detected in the joint brazed at adopted temperatures, which mainly dominated by eutectic reactions and driven by cooling. The ASZ decreased shear strength of the defect-free joint, and readily accelerated initiation and propagation of cracks. The maximum shear strength of 554 MPa was obtained when the joint was brazed at 1120 °C for 10 min. The fracture mainly occurred in the ASZ (semi-cleavage), and passing through the DAZ (semi-cleavage) and ISZ (dimples).
查看更多>>摘要：? 2022 Elsevier Inc.We studied nucleation and growth of Ag precipitates in a Cu-6 wt%Ag-0.15 wt%Sc alloy and found that the early nucleation of Ag precipitates was similar to continuous precipitation in that it occurred only on dislocations within Cu grains, not on any grain boundaries. In aged samples, we observed stacking faults that extended into nanotwins. These planar defects formed during early nucleation of Ag precipitates and extended into the surrounding Cu matrix. The formation of planar defects released misfit strain on Cu/Ag interfaces, enhancing subsequent nucleation and growth of Ag precipitates. Unlike the intrinsic defects found in previous research, these defects were clearly extrinsic. The planar defects provided a row of additional sites aligned along twin boundaries for the nucleation of Ag precipitates. The formation of new Ag precipitates, by reducing dissolved Ag in the Cu matrix, increased conductivity significantly. Planar defects reduced electrical conductivity somewhat, but the synergy between Ag precipitation combined with planar defects had the effect of substantially increasing both hardness and conductivity.
查看更多>>摘要：? 2022In this paper, two groups of Nb/Ti low carbon microalloyed steels (Nb-bearing and Nb-free) were obtained through laboratorial methods. The evolution and effect of Nb/Ti-containing complex inclusions were characterised and analysed after being subjected to high heat input thermal simulation of 100 kJ/cm. The results showed that the prior austenite grain size in the coarse grain heat-affected zone (CGHAZ) was not affected by 0.045 wt% Nb addition. However, the acicular ferrite nucleation, induced by effective micron-level inclusions, was inhibited. Nb tended to converge towards the interfaces between the micron-level inclusions and matrix, which had a negative effect on the nucleation potential of acicular ferrite. The re-precipitation behaviour of nano-level inclusions satisfied the dynamic conditions during the high heat input thermal cycle, under which the dislocation movement was inhibited due to the pinning effect of re-precipitation particles. Besides, the size, morphology and composition of nano-level precipitates were changed by Nb (0.045 wt%) addition. In general, the evolution and effect of inclusions in simulated high heat input CGHAZ provide theoretical references for the study of welding performance in Nb/Ti low carbon microalloyed steels.
查看更多>>摘要：? 2022 Elsevier Inc.The role of AlN on the internal oxidation behavior was investigated in Al-containing high Mn steels. Accelerated internal oxidation behavior was confirmed as Al contents increased. The sequential formation of internal oxidation and AlN + γ-matrix layers on the γ-matrix was observed in Al-containing steel after the heat-treatment in air. The former AlN + γ-matrix layer was replaced with the internal oxidation layer as the oxidation progressed. The heterogeneous nucleation of MnAl2O4 on the AlN was identified in between the internal oxidation and AlN + γ-matrix layers. MnAl2O4 shows the 101ˉ0AlN//112MnAl2O4 and 0001AlN//111ˉMnAl2O4 orientation relationship with the pre-existing AlN by sharing Al atoms. The coherency between MnAl2O4 and AlN and the evolution of oxides in Al-containing high Mn steels were further discussed.
查看更多>>摘要：? 2022 Elsevier Inc.This paper systematically studied the microstructure and phase formation sequence in the powder in tube (PIT) Nb3Al processed by rapid heating and quenching (RHQ), which is a crucial issue to fabricate reliable high performance practical Nb3Al superconductors. Due to significantly inhomogeneous of the Nb/Al diffusion couple distance, an eutectic phase with liquid characteristic happened during the RHQ process, where the phase formation sequence is: Nb + Al → eutectic phase + NbAl3 → Nb3Al + Nb2Al → grid morphology bcc → band feature bcc with the increase of rapid heating temperature. The phase and microstructure during RHQ are mainly determined by the RHQ condition and local Nb/Al distribution that similar feature was shown in the quenched wires with initial Al content of 22–28 at.% in the raw powders. Grid and band microstructure of the bcc phase was related to the Al content of ~32 at.% and ~ 22 at.%, respectively. After transformation process at 800 °C, quenched wires with coexist of gird and band micro-structure show the best superconducting properties, including Tc, ΔTc, Birr, and Jc. The microstructure identification confirms that uniform and thin Al layer in the precursor wire plays an essential role in obtaining a homogeneous bcc solid phase.
查看更多>>摘要：? 2021In this work, a novel high damping Mg-1.5Gd binary alloy with ultrahigh ductility and adequate strength was prepared by hot extrusion at different temperatures of 360 °C, 420 °C and 480 °C. The microstructure, damping capacity and mechanical properties of the as-extruded alloys were systematically investigated. The results showed that the tensile elongation of all as-extruded Mg-1.5Gd alloys is over 40%, which is mainly ascribed to the formation of the <21-1-1> rare-earth (RE) texture component in alloys after hot extrusion, and the highest damping value Q?1 is 0.086 at ε = 10?3. In addition, the relationship between the strain amplitude and damping value Q?1 fit the Granato-Lücke (G-L) dislocation theory for the alloys well. The damping capacity of the alloys was discussed in detail in terms of the dislocation motion and G-L plot. Under the same comparison conditions, the damping value Q?1 and yield strength of the Mg-1.5Gd alloy extruded at 360 °C were higher than those of Mg-1Y and comparable with those of Mg-0.6Zr considered to be a typical high damping alloy. This implied that dilute wrought Mg-Gd binary alloys containing RE textures exhibited promising potential for developing high-performance damping alloys in terms of both damping capacity and yield strength.
查看更多>>摘要：? 2022 Elsevier Inc.This work investigates the effect of adding SiC nanowires (SiCNWs) on the microstructure and mechanical properties of Mg-2Zn-0.1Y matrix composites under different hot extrusion parameters, and the strengthening mechanism was analyzed. The results showed that as the extrusion temperature elevated from 140 °C to 220 °C or the extrusion speed increased from 0.1 mm/s to 1.0 mm/s, both the dynamic recrystallized grain size and the recrystallized volume fraction increased significantly. The changes of precipitate size and volume fraction exhibited the same trend. The finest recrystallized grains (~0.37 μm) were obtained after extrusion at 140 °C and 0.1 mm/s, which also contained nano-sized MgZn2 precipitates and SiC nanowires. As the extrusion temperature increased from 140 °C to 220 °C at a constant extrusion speed of 0.1 mm/s, the strength of the composites decreased while the elongation improved greatly. Similar change in the strength and elongation were obtained in the composite as the extrusion speed increased from 0.1 mm/s to 1.0 mm/s at extrusion temperature of 140 °C. Meanwhile, these composites exhibited a weakened texture, and a mixture of microcracks and dimples was observed in the fracture surfaces of the as-extruded composites, which explained the mix of brittle-ductile fractures of the composites. The composites extruded at 140 °C and 0.1 mm/s exhibited the best performance with yield strength (YS) and ultimate tensile strength (UTS) of ~495.53 MPa and ~514.18 MPa, respectively. Among all strengthening mechanisms, the proportion of grain refinement strengthening is the highest.
查看更多>>摘要：? 2022 Elsevier Inc.Among cubic metals, the cubic phase has excellent heat-resistance potential owing to its cube-on-cube orientation relationship with the matrix. In this study, a new cubic phase, Al5Cu6(Li,Mg)2, was identified in an Al-Cu-Li-Mg-X alloy after ageing at 165 °C for 15 h. It has a Pm3 structure similar to that of both Al5Cu6Li2 and Al5Cu6Mg2. The density functional theory (DFT) calculations noted that the precipitation of Al5Cu6Li2 is more energetically favorable than that of Al5Cu6Mg2 in the Al-Cu-Li-Mg-X alloy. Moreover, the formation enthalpy may be further reduced when the Mg atoms replace some Li sites in Al5Cu6Li2, in favor of the formation of Al5Cu6(Li,Mg)2.
查看更多>>摘要：? 2022Magnesium?lithium (Mg–Li) alloys have been widely used in various engineering fields due to their ultra-light characteristics. The strengthening of Mg–Li alloys is one of the key factors determining its application and has received extensive attention. In this work, the as-cast ultralight and high strength Mg-10Li-3Al-3Zn-xY (x = 0, 0.5 and 1.0, wt%) alloys with a density of only 1.52 g/cm3 were prepared via vacuum induction melting. The effects of rare earth element yttrium (Y) on the microstructure and mechanical properties of the Mg–Li alloy system were investigated. The results indicated that the microstructures of all the alloys mainly consisted of α-Mg, β-Li, AlLi, and MgLi2Al phases. The spherical AlLi phase was distributed inside the α-Mg and β-Li matrix. Part of the petal-like MgLi2Al phase was distributed in the interior of β-Li, and the rest grew along the grain boundaries as long strips. With the addition of Y, Al2Y phase formed with sharp edges and regular shapes. The Al2Y phase was mainly distributed inside the α-Mg phase and along the grain boundaries. Meanwhile, the amount of AlLi phase inside the α-Mg phase gradually decreased. The presence of nano-scale lath-shape MgLiZn phase in the β-Li matrix was observed in the HAADF map of the 0.5Y alloy. The continuous growth of MgLi2Al phase at the grain boundaries weakened its strength. As a consequence, it eventually led to intergranular fracture of the alloy. The 0.5Y alloy showed the highest tensile strength, up to ~244 MPa, and the yield strength was 60.5% higher than that of the 0Y alloy. Solid solution strengthening, precipitate strengthening and grain refinement were thus considered as the primary strengthening mechanisms caused by the addition of Y into the Mg-10Li-3Al-3Zn alloy.
NSTL
Elsevier