查看更多>>摘要：? 2022 Elsevier Inc.Wire arc additive manufacture is well applied in the fabrication of Al-5.0 Mg products. The investigation of microstructure morphology and phase composition in different regions is not enough. Therefore, the factors of microstructure morphology, dislocations densities and phase composition are worthy to study. Investigations of microstructure morphology demonstrated that the cross-section along the deposition direction has diversified grain size and the diversity increases the dislocation density and decreases the residual stress. The preferred orientation of grain growth analyzed by XRD explained that the decreasing intensity of (200) could improve the homogeneity. EDS results revealed that Al and Al3Mg2 were the main phases. TEM results demonstrated that there was Al2Mg formed inside grains and the irregular shapes of precipitations. The temperature gradient in the two regions is the main factor causing the differences in dislocation density, precipitations formation and microstructure diversity
查看更多>>摘要：? 2021The 3D printing technology is gradually applied on oxide dispersion strengthened (ODS) steels to address its processing issue and prepare complex components for generation IV nuclear reactor. However, the nanoparticles always aggregate and coarsen during the printing process because of the severe repining behavior in the high-temperature melt. This leads to a large degradation of the strengthening effect of nanoparticles. This study proposes a strategy of in situ synthesis of nanoparticles in ODS steel during the printing process by using pre-alloyed powder with controlling the partial pressure of oxygen to overcome the abnormal growth behavior of nanoparticles. After printing, a large number of nanoparticles were in situ formed and distributed uniformly in the ODS steel. The average size and number density of nanoparticles were ~ 21.09 nm and ~ 4.1 ± 0.5 × 1021/m3, respectively. As compared with the majority of 3D printed ODS steels from mechanical alloyed powder, the in situ formed nanoparticles in this study exhibit the combination of smaller size, higher number density, and better distribution homogeneity and size uniformity. This provides an outstanding secondary strengthening effect and produces ODS steel with the UTS and YS of printed ODS steel are 725 and 673 MPa, respectively. In addition, the microstructural characterization and formation mechanism of nanoparticles in this newly printed ODS steel are also given and discussed in detail.
查看更多>>摘要：? 2022 Elsevier Inc.Achieving an excellent combination of mechanical properties and electrical conductivity in conductive copper alloys is highly desirable but remains a great challenge. This paper reports a dual heterogeneous laminated (DHLed) Cu/Cu-Cr-Zr composite structure in copper alloys produced by accumulative roll bonding (ARB) and annealing process that can produce an excellent property combination: high strength (ultimate tensile strength: 563.4 ± 14 MPa), sufficient tensile ductility (uniform elongation: ~16.2%), and high conductivity (~92%IACS). The specially designed DHLed Cu/Cu-Cr-Zr composite microstructure is characterized by alternating coarse- and ultra-fine grain layers and layered distribution of precipitations. Such dramatic microstructure heterogeneities produce significant hetero-deformation induced hardening due to mechanical incompatibility between soft Cu and hard Cu-Cr-Zr layers, which leads to an excellent combination of strength and ductility. The high conductivity can be attributed to the unique DHLed Cu/Cu-Cr-Zr composite structure containing alternating recrystallized- and nanolaminated-grain layers.
查看更多>>摘要：? 2022 Elsevier Inc.Due to the unique microstructure, nanoporous materials, have great potential application in the fields of catalysis, sensing and fabrication of advanced materials. This study mainly focuses on the thermal decomposition mechanism of ammonium paramolybdate and nanoporous flake molybdenum powder fabrication. The decomposition process was clarified and verified. The approximate molar formation enthalpy and some thermodynamic data of ammonium paramolybdate and its related decomposition products under experimental conditions were estimated by enthalpy change values of decomposition reaction in the various stages. Nanoporous flake molybdenum powder was fabricated by sol-gel reduction method at different pH values. The mechanism of transition from ammonium paramolybdate to molybdenum powder was elucidated. The results show that the morphology of products in each stage is hereditary. With the increase of pH value, the reaction was complete and the powder morphology gradually became flake and the shape distribution was uniform and distribution. When the pH is 5, through inert gas passivation treatment, the final molybdenum powder has a uniform particle size of about 65 nm and a specific surface area of about 7.5 m2/g. The nanoporous powder with such a special morphology and microstructure has potential prospects in the field of functional materials such as catalysis.
查看更多>>摘要：? 2022 Elsevier Inc.This work investigates the strain rate dependence of deformation and dynamic recrystallization (DRX) behaviors of basal-textured AZ80 magnesium alloy, in the hot compressions at 350 °C with varying strain rates of 10?3 s?1 and 10 s?1. Hot compressed microstructure was characterized using electron backscatter diffraction (EBSD) with grain-based analytical approaches, providing insights into the operative dynamic recrystallization mechanisms and correlated texture evolution. At small strain levels, discontinuous DRX mechanism was dominant at 10?3 s?1 and stress concentrations between the neighboring grains were effectively relieved by grain boundary bulge and growth of DRXed nucleus. In contrast, at 10 s?1, twin-induced DRX and continuous DRX mechanisms were activated. Off-basal-oriented grains (soft) were consumed rapidly by the operative DRX processes, while basal-oriented grains (hard) show less tendency to recrystallize. At the interphase between the residual basal-oriented grain and the neighboring DRXed grains, intergranular micro-cracks initiated in the incipient stage of the hot compression at 10 s?1, due to the absence of effective strain releasing mechanism. The results have implications for hot workability improvement for AZ80 magnesium alloy under high-strain-rate conditions.
查看更多>>摘要：? 2022 The Author(s)Improving the hot workability of cast and wrought Ni-base superalloys is complex due to grain boundary cracking. Mitigation approaches focus on grain boundary active microalloying elements B and Zr. René 41 is one of few superalloys with exceptional high-temperature strength required for next-generation aircraft engine components. Its grain boundaries are decorated by solutes and γ', carbide, and/or boride precipitates. However, the detailed influence of B & Zr additions on the hot workability and grain boundary decoration of superalloys like René 41 remain unexplored. To address this knowledge gap, we industrially manufactured two René 41 variants, a nominal and a high B & Zr one. Correlative microscopy reveals γ' and M2B grain boundary precipitation as supported by thermo-kinetic modeling. Site-specific atom probe microscopy reveals the interfacial excess close to those grain boundaries most prone to cracking. In the nominal variant, γ'/γ interfaces are less decorated by B, C and Zr with 4.6 atoms nm?2. γ/γ interfaces are saturated at ~ 5.8 atoms nm?2 in both variants. Grain boundary pinning of M2B is increased by Zr promoting γ' precipitation, causing grain boundary cracking. Optimized solute concentrations are proposed. Based on our findings the next iteration of superalloy design using microalloying is enabled.
查看更多>>摘要：? 2022 Elsevier Inc.In this paper, the effect of artificial aging (AA), solution heat treatment (SHT) and solution heat treatment + artificial aging (SHA) at different time and temperature on the microstructures and compression properties of AlSi10Mg lattice structures manufactured by selective laser melting (SLM) were systematically investigated. The microstructure of as-built sample consists of elongate cellular α-Al matrix decorated with eutectic Si network boundaries. After AA, the cellular structure is still maintained and there are a lot of nano-sized Si precipitates of the cellular structure. After SHT and SHA, the unique microstructural characteristic of as-built disappear, whereas the Si-rich cellular boundaries are transformed into Si particles and Si particles become coarse. The Si particles inhibit grain growth in the α-Al matrix, the samples have a strong 〈001〉 orientation. The digital image correlation (DIC) method was adopted to analyze the strain field and strain distribution during the compressive process. The results reveal that the SHA has the best compression properties and stable deformation mode. And the fracture mode changed from the initial brittle fracture to ductile fracture. The correlation between the microstructure evolution and the compression properties and the strengthening mechanism were discussed. Finally, the finite element analysis was carried out to simulate the static response of the lattice structure based on the optimal heat treatment parameters. The results can be used as a reference for control of the microstructure characterization and compression properties of AlSi10Mg lattice structure after heat treatment.
查看更多>>摘要：? 2022Ar ion bombardment was applied to modify the aluminum surface and a subsequent solid-state diffusion bonding was performed. The effect of Ar ion bombardment on surface conditions and properties was studied to analyze the relationship between surface modification and joint performance. With increase of the Ar ion energy, the surface oxide film was removed and its surface roughness tended to decreased first and then increased. The oxide-free aluminum surface with minimal roughness of 0.61 nm was obtained by 1 keV bombardment while the numerous small dislocation loops uniformly distributed in the aluminum surface structure enhanced the surface hardness. Under high-energy bombardment (>5 keV), the surface became swollen or even porous due to the growth of dislocation loops and Ar bubbles that made the surface rough and embrittled, which deteriorated the microstructure and strength of bonded joints. The well-bonded joint with shear strength of 45.9 MPa was obtained at 1 keV bombardment and diffusion bonding temperature of 450 °C. The specific shear strength of ~60% was higher than that of conventional Al diffusion bonded joints. This work is of significance for the manufacture of well-bonded aluminum microchannel heat exchangers.
NSTL
Elsevier