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The accelerated creep failure of Ni-based single crystal superalloy by hot corrosion is confirmed by creep tests at 900 °C/550 MPa–400MPa in air and salt environments. The analysis of creep curve, microstructure and fracture type shows that there are obvious differences in hot corrosion-creep behavior under high, middle and low creep stress conditions, indicating that there is the stress dependence between the influence of hot corrosion on the creep properties of the alloy. Hot corrosion accelerates creep failure of Ni-based single crystal superalloy by decreasing the deformation resistance, reducing the effective stress area, and affecting the creep fracture mode. [ABSTRACT FROM AUTHOR]

Abstract: The deformation and fracture process in Al–Cu–Mg alloy were investigated by using the in situ straining transmission electron microscopy (TEM) method. Some major aspects of the fracture process, including dislocation emission and migration, thinning of dislocation free zone (DFZ), crack propagation (both in continuous and discontinuous manners) and slipping/twinning deformation, can be observed. The rod-like T dispersoids, which may increase the microcrack initiation sensitivity, also can effectively prevent the fast and continuous propagation of the crack. DFZ ahead of crack tip can be thinned in a mixed mode characterized by tearing and shear deformation, while nanovoids, which are typical characteristics in DFZ during discontinuous crack propagation, may originate from the enrichment of defects such as dislocations and vacancies. Deformation twinning at crack tip can slow down crack propagation and change crack propagation path, thus may be beneficial to the fracture toughness of the alloy. [Copyright &y& Elsevier]

Abstract: Effect of interfacial shear strength on longitudinal tensile properties for SiCf/Ti–6Al–4V composites is investigated by Monte Carlo finite element method. A two-parameter Weibull function is employed to describe random distribution of fiber strength. Fiber breakage, matrix cracking and interfacial debonding are simulated by killing the element when stress applied to element exceeds corresponding strength and releasing coupled nodes when shear stress exceeds shear strength at interfaces. The results show that tensile strength of SiCf/Ti–6Al–4V composites keeps unchanged for various interfacial shear strengths, but low interfacial shear strength is advantageous to reduce catastrophic failure. Moreover, with low interfacial shear strength, fiber breakage in the composites is more inclined to be non-coplanar. In addition, tensile strength obtained from finite element method is compared with those predicted by global load-sharing model (GLS), local load-sharing model (LLS) and conventional rule of mixtures (ROM) and is identical with that obtained from LLS. [Copyright &y& Elsevier]

Abstract: The plasticity of AZ31 and ZK60 magnesium alloys was studied by means of hot compression deformation tests on Gleeble 1500D machines at different temperatures and strain rates. The results indicate that the thermal simulation curves of AZ31 and ZK60 have different forms under the same deformation condition. The general curves of AZ31 have the character of dynamic recrystallization that the flow stress increases to a peak and then decreases to a steady state. Most deformation curves of ZK60 have the obvious character that around 0.2 in strain the stress reaches the peak and declines rapidly to the lowest, while the other curves have the character of dynamic recrystallization. From the analysis, a deformation temperature should reasonably be selected from 250°C to 400°C for AZ31, while it was concluded to be 200°C or 400°C for ZK60. [Copyright &y& Elsevier]

Abstract: SiC fiber reinforced copper matrix composites were prepared by foil-fiber-foil method (FFF) and, fiber-coating method (MCF) with and without a Ti6Al4V interlayer, respectively. The copper coating was prepared by different electroplating processes and the Ti6Al4V interlayer by magnetron sputtering. The results show that the tensile strengths of specimens without Ti6Al4V interlayer are nearly identical and poor, between 250 and 290MPa, while the ones of specimen with Ti6Al4V interlayer can be greatly improved, over 500MPa. This great increase attributes to the improvement of the SiC/Cu interfacial bonding strength because the interfacial reactions occur at Cu/Ti6Al4V interface and Ti6Al4V/SiC interface. Additionally, there are generally many micropores produced by hydrogen and oxygen in the electroplated coating, which would influence the density of the matrix. Therefore, the densification of the matrix was worth investigating since it would influence the thermal and electrical conductivity of the composite, though it has only a little contribution to the tensile strength. Experiments indicate that proper heat-treatment before hot pressing could improve the densification of the matrix. [Copyright &y& Elsevier]

Abstract: Ti6Al4V/TA1 diffusion couples were fabricated and then heat-treated in vacuum under different conditions. The metallographic structure, morphologies and the composition distribution in diffusion bonding zone were investigated by means of OPM, SEM and EDS. The results indicate that the diffusion couples are bonded well; the alloying elements Al and V diffuse from Ti6Al4V to TA1, and Ti atoms diffuse in the opposite direction. The transition zone of the alloying elements obeys a rule of parabolic rate. At the same time, based on Koher''s ternary solution model and Miedema''s model for calculating the thermodynamical interaction coefficients, the theoretical diffusion profiles of Ti and alloying elements are obtained according to the inter-diffusion coefficients of the alloying elements and the numerical solution of the phenomenological equation. Moreover, the calculated values are well fitted to the experimental data. So the distribution of the diffusion atoms can be predicted at the diffusion bonding interface. [Copyright &y& Elsevier]

Based on shear-lag method, two models for a single fiber push-out test are proposed to evaluate the interfacial shear strength of SiC fiber-reinforced titanium-matrix composites (TMCs). In the models, the effects of specimen parameters (such as specimen thickness and fiber volume fraction) on the interfacial shear strength are considered. The interfacial shear strengths of SCS-6/Ti-24-11 and SCS-6/Ti-15-3 composites are predicted using the model. The predicted results indicate that the models can be reliably used to predict interfacial shear stress of TMCs. [ABSTRACT FROM AUTHOR]

Cryorolling (CR) can effectively avoid room temperature rolling cracking of high-strength aluminum alloy. In this work, solution-treated bulk Al 7085 alloy samples were subjected to CR and room temperature rolling (RTR), respectively. When the deformation was 70%, the RTR sample was broken, while the CR one still had no cracks when the deformation was up to 90%. Consequently, the microstructure and mechanical properties of the CR samples before and after ageing treatment were investigated. The results show that after the solution-treated bulk Al 7085 alloy samples were cryorolled, the yield strength (YS) and the ultimate tensile strength (UTS) were increased by 74% and 31%, respectively. However, the elongation to failure (EtF) was decreased. After the subsequent 100 °C/20 h peak ageing (PA) treatment, the YS and UTS can be further increased by 14% and 10%, respectively, and the EtF was increased by 39% compared with that of the CR samples. After PA treatment, nanosized GP zones and η′ precipitates were precipitated. Precipitation strengthening is the main contributor to the strength enhancement of CR samples after PA treatment, which can not only compensate for the reduction caused by the decrease in dislocation density but also improve the strength of the material. • Al 7085 alloy was processed by cryorolling and subsequent ageing treatment. • Strength and ductility of the cryorolled sample can be simultaneously improved after peak ageing treatment. • The aged sample contains nanosized GP zone and η′ precipitates. • Precipitation strengthening is the main contributor for strength enhancement of the cryolled + peak aged sample. [ABSTRACT FROM AUTHOR]

Novel Al 2 O 3 nanoparticle-reinforced heterogeneous CrCoNi-matrix composites (CrCoNi–Al 2 O 3P) with 10–30 wt% of coarse grain (CG) matrix were prepared by multi-step mechanical milling plus hot pressing sintering. The relationships between microstructure and mechanical properties of the composites were studied in detail. The results reveal that the heterogeneous structure in CrCoNi–Al 2 O 3P composites is composed of CG region and ultrafine grain (UFG) region with uniform distribution of Al 2 O 3 nanoparticles. With increasing content of CG matrix in the nanocomposite, the hardness first decreases but then increases, and the increase of hardness may be due to the formation of carbides. Compared with homogeneous CrCoNi–Al 2 O 3P composite, the compressive fracture strain of heterogenous composite increases by 53.2% at most, while sacrificing a small amount of strength, among which the 20 wt% CG heterogeneous composite exhibits an excellent strength-ductility synergy. For the mechanisms of strengthening and toughening, hetero-deformation induced (HDI) hardening makes the heterogeneous composites almost as strong as the homogeneous composite. Meanwhile, the CrCoNi matrix with low stacking fault energy can be deformed by dislocation slipping and twinning at room temperature, which improves the plasticity of the composite. Furthermore, the heterogeneous structure with soft and hard domains increases the work hardening ability of the composite. ● Heterogeneous matrix of CrCoNi–Al 2 O 3 composites was successfully prepared via multi-step mechanical milling plus hot pressing sintering. ● The composites contain CG region, UFG region with Al 2 O 3 nanoparticles and annealed twins in the matrix grains. ● The fracture strain of 20 CG heterogeneous composite increases distinctly and the strength remains high. [ABSTRACT FROM AUTHOR]

Cryorolling (CR) can effectively avoid room temperature rolling cracking of high-strength aluminum alloy. In this work, solution-treated bulk Al 7085 alloy samples were subjected to CR and room temperature rolling (RTR), respectively. When the deformation was 70%, the RTR sample was broken, while the CR one still had no cracks when the deformation was up to 90%. Consequently, the microstructure and mechanical properties of the CR samples before and after ageing treatment were investigated. The results show that after the solution-treated bulk Al 7085 alloy samples were cryorolled, the yield strength (YS) and the ultimate tensile strength (UTS) were increased by 74% and 31%, respectively. However, the elongation to failure (EtF) was decreased. After the subsequent 100 °C/20 h peak ageing (PA) treatment, the YS and UTS can be further increased by 14% and 10%, respectively, and the EtF was increased by 39% compared with that of the CR samples. After PA treatment, nanosized GP zones and η′ precipitates were precipitated. Precipitation strengthening is the main contributor to the strength enhancement of CR samples after PA treatment, which can not only compensate for the reduction caused by the decrease in dislocation density but also improve the strength of the material. • Al 7085 alloy was processed by cryorolling and subsequent ageing treatment. • Strength and ductility of the cryorolled sample can be simultaneously improved after peak ageing treatment. • The aged sample contains nanosized GP zone and η′ precipitates. • Precipitation strengthening is the main contributor for strength enhancement of the cryolled + peak aged sample. [ABSTRACT FROM AUTHOR]

Novel Al 2 O 3 nanoparticle-reinforced heterogeneous CrCoNi-matrix composites (CrCoNi–Al 2 O 3P) with 10–30 wt% of coarse grain (CG) matrix were prepared by multi-step mechanical milling plus hot pressing sintering. The relationships between microstructure and mechanical properties of the composites were studied in detail. The results reveal that the heterogeneous structure in CrCoNi–Al 2 O 3P composites is composed of CG region and ultrafine grain (UFG) region with uniform distribution of Al 2 O 3 nanoparticles. With increasing content of CG matrix in the nanocomposite, the hardness first decreases but then increases, and the increase of hardness may be due to the formation of carbides. Compared with homogeneous CrCoNi–Al 2 O 3P composite, the compressive fracture strain of heterogenous composite increases by 53.2% at most, while sacrificing a small amount of strength, among which the 20 wt% CG heterogeneous composite exhibits an excellent strength-ductility synergy. For the mechanisms of strengthening and toughening, hetero-deformation induced (HDI) hardening makes the heterogeneous composites almost as strong as the homogeneous composite. Meanwhile, the CrCoNi matrix with low stacking fault energy can be deformed by dislocation slipping and twinning at room temperature, which improves the plasticity of the composite. Furthermore, the heterogeneous structure with soft and hard domains increases the work hardening ability of the composite. ● Heterogeneous matrix of CrCoNi–Al 2 O 3 composites was successfully prepared via multi-step mechanical milling plus hot pressing sintering. ● The composites contain CG region, UFG region with Al 2 O 3 nanoparticles and annealed twins in the matrix grains. ● The fracture strain of 20 CG heterogeneous composite increases distinctly and the strength remains high. [ABSTRACT FROM AUTHOR]

Improving surface properties can effectively expand the industrial application of aluminum alloys. In this study, a gradient nanostructured surface layer was successfully fabricated in an aged Al–Zn–Mg–Cu alloy by ultrasonic surface rolling processing (USRP). The microstructure and microhardness of the gradient nanostructured surface layer were investigated. The results show that a perfect gradient lamellae structure was fabricated in the surface layer. The average structural size in the topmost surface layer is approximately 41 nm, and the depth of nanostructure lamellae layer is up to 50 μm. After the USRP and two years of natural aging, the gradient distribution of precipitates was formed in gradient lamellae structure. A large number of discontinuous coarse η phase are formed on the lamellae boundary throughout the lamellae structure. However, the precipitates inside the lamellae have gradient distribution. The volume fractions of precipitates increase gradually from nanostructure to ultrafine-grained structure, and the main precipitates are GPII zones. The microhardness in the topmost surface is increased by 40% and gradually decreases from the surface to the matrix. The increase in microhardness is attributed to the fact that the enhancement of the hardness by the grain refinement is greater than the decrease due to the reduction of the precipitates inside the gradient lamellae structure from the surface to the matrix. This study provides technical method and theoretical basis for improving the surface hardness of Al–Zn–Mg–Cu alloy. [ABSTRACT FROM AUTHOR]