查看更多>>摘要：? 2022 Elsevier Inc.The present investigation is mainly focused on friction stir additive manufactured (FSAM) 2195 Al-Li alloy in aspects of localized microstructure evolution and mechanical performance. Characterization of the localized microstructure was conducted by optical microscope (OM), electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM) techniques, and mechanical properties were evaluated based on micro-hardness and tensile testing measurements. Results showed a build of multilayered stack of 2195 aluminum lithium alloy was fabricated using FSAM via multi-pass processing. Defects such as voids or kissing bond were not identified, and fine equiaxed grains were observed in the nugget zone (NZ). The decrease of average grain size and low angle boundaries (LABs) along the depth of the NZ was attributed to repetitive stirring action of the rotating tool. Distribution of precipitation phase is mainly determined by the thermal cycle. Numerous T1 and θ′ precipitates were identified in the base material (BM), which are beneficial to improve material hardness and thus strength. These precipitates were dissolved in NZ and thermo-mechanically affected zone (TMAZ), and coarsen in heat affected zone (HAZ), which caused loss of hardness and strength. Similarly, precipitate morphology, size, and distribution are different in the built direction. Excellent tensile strength and elongation were identified in the NZ, which is attributed to fine grains and desirable precipitate characterization.
查看更多>>摘要：? 2022 Elsevier Inc.In order to achieve the combination of mechanical and corrosion properties for 7050 alloy, a novel retrogression and re-aging regime were proposed in this study. During the retrogression, the pre-aged alloys were heated from room temperature to 190 °C with different retrogression heating rates, and then were cooled quickly for following re-aging treatment. The size of precipitates and the width of precipitation free zones decreased with the increasing retrogression heating rate, the mechanical properties of 7050 alloy were improved, while the corrosion resistance was reduced. When the retrogression heating rate was controlled at 3 °C/min, a good combination of strength and corrosion resistance of 7050 alloys could be obtained. The excellent properties were attributed to the homogeneous distribution of intragranular precipitates (η’) and the coarsening of intergranular precipitates (η) after the novel retrogression and re-aging regime.
查看更多>>摘要：? 2022 Elsevier Inc.In this paper, the mechanical properties of pure tantalum (Ta) hat-shaped samples during dynamic impact were studied, and microstructures at different reductions were characterized. Results showed the ultrafine grains formed in adiabatic shear band (ASB). When the reduction is 40%, that is to say that the shear strain is 4, the shear yield strength is about 703.65 MPa, and then the shear stress decrease with increasing strain. ASB is formed and could be divided into transition and central regions. Most of the grains in the central region are ellipsoidal dynamically recrystallized (DRX) grains with a size of about 760 nm, while numerous grains in transition region are split. The geometric necessary dislocations (GNDs) density (20.13 × 1014 m?2) in the transition region is greater than the density (18.28 × 1014 m?2) in the central region. The average hardness of the matrix region is about 88.80 HV, and the value in the ASB reaches 239.08 HV. The maximum temperature within the ASB is calculated to be approximately 1100 K before ASB formation. According to the mechanically driven subgrains rotation model, subgrains inside ASB slip and rotate under the action of shear forces or normal stresses, and finally a texture 〈110〉 // shear plane normal (SPN) near the top of ASB and 〈110〉 // shear direction (SD) near the bottom is formed.
查看更多>>摘要：? 2022 Elsevier Inc.The tensile crack initiation and propagation of M50 bearing steel were investigated. It is found that the primary carbides were fractured during the tensile test by in situ SEM, while decohesion of the carbide/matrix interface was hardly observed. In order to capture the initial tensile crack, quasi-in situ X-ray microtomography was performed, indicating that the earliest crack was formed from the broken interior carbides. This indicates that multiple cracks already existed in the matrix when they were observed on the sample surface. Electron backscattered diffraction (EBSD) and the finite element method (FEM) were applied to analyze the fracture behavior of carbide particles. The fracture of carbide particle is produced by the incompatible deformation between the matrix and carbides. The frequency of carbide fracture was found to be related with its fracture strength, size and shape. M2C carbide fracture was more easily broken than the MC carbide during tensile test. In addition, the long axis of most M2C carbides is approximately parallel to its (0001) plane and normal to tensile stress, leading to cracking more easily. Finally, a suggestion of adding pre-deformation is proposed to make M2C carbides broken sufficiently and further refine the primary carbides.
查看更多>>摘要：? 2022 Elsevier Inc.Minor additions of rare-earth elements improve the mechanical properties of aluminum-based alloys due to precipitation strengthening, increased recrystallization resistance, and grain refinement effects. This study investigated the microstructure, room temperature mechanical properties, and superplasticity of Al–Mg–Z–Er alloys with the Mg content in a range of 2.1–4.9 wt%. The alloys' microstructure was presented by an Al-based solid solution matrix enriched with Mg, the (Al,Mg)3Er phase of solidification origin, and nanoscale secondary precipitates of the Al3(Er,Zr) L12–structured phase. The Al3(Er,Zr) precipitates provided the Orowan strengthening mechanism, led to a strong recrystallization resistance and the Zener pinning effect during elevated temperature deformation. An increase of the Mg solute resulted in a solid solution strengthening and facilitated dynamic recrystallization at elevated temperatures. In the alloy with 4.9%Mg, a combined effect of fine L12 precipitates, high solute Mg, and (Al,Mg)3Er particles led to a fine-grained structure formation and superplasticity with the maximum strain rate sensitivity m of 0.51 and the elongation-to-failure of 550–600% at the constant strain rates of (0.8–1) × 10?2 s?1. The mechanical properties at room temperature were studied after the post-deformation annealing of the thermomechanically treated alloys and after the superplastic deformation. The developed Arrhenius-type mathematical model of superplastic deformation behavior showed excellent predictability for the studied alloys with different solute Mg.
查看更多>>摘要：? 2022Tracking texture evolution during in situ loading is critical to understand and simulate the dynamic behaviour of microstructure in polycrystalline materials, yet conventional texture quantification methods are sometimes restricted due to various factors, such as acquisition time, sample environment and complex setup. To address this, a novel approach to extract texture information from single shot Time-Of-Flight neutron diffraction pattern has been developed. Another texture analysis approach based on single shot synchrotron X-ray diffraction has also been demonstrated. The effectiveness of two methods is assessed for polycrystalline Nickel-based superalloy polycrystalline samples possessing different textures. Both methods feature a moderate acquisition time of ~10 min and 30 s respectively, as well as a simplified setup which allows adding complex sample environments and the use of additional equipment. Comparison with the referential EBSD texture suggests that both approaches achieve a satisfactory match, though some details of the complex contour profiles in inverse pole figures may be missing. Besides that, a novel metric has been proposed to quantify the matching quality of pole figures. By employing the EPSC modelling approach, it is shown that the texture deviation due to the technique chosen for its evaluation exerts a subtle influence on th macro- and mesoscale simulation results, highlighting the significance of this approach for underpinning robust computational modelling.
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