查看更多>>摘要：? 2022 Elsevier Inc.The link between microstructure, crystallographic texture and mechanical properties is of substantial importance to the understanding of materials behaviour of aluminium alloys. The favoured approach to determine these relations has been electron backscatter diffraction (EBSD) and has received extensive prior attention. However, compared to conventional optical microscopy, EBSD is both cost and potentially time intensive limiting its viability as a widespread method in industrial quality assurance. Following early successes by the authors and other investigators with optically birefringent metals, this investigation assesses the suitability of reflected circular polarized light microscopy (CPLM) as a rapid low-cost alternative to EBSD for cubic systems. Direct comparisons between EBSD crystal orientation maps (COMs) and a quantitative determination of the character of reflected polarized light images is presented to demonstrate that this technique can provide quantitative texture information for aluminium. Further, the inherently surface sensitive nature of the technique allowed further verification of orientation relationships between the substrate and surface oxide only previously made possible by high resolution transmission electron microscopy.
查看更多>>摘要：? 2022 Elsevier Inc.The influence of rare earth on the microstructures as well as properties of Al and its alloys has attracted great attention recently. However, contradictory results always were reported, some previous studies found that rare earth promoted the increment of the tensile properties of Al alloy, some other researchers though rare earth had no significant effect on the tensile properties or decreased the tensile properties. In the present work, the effects of minor rare earth element La on the solidification, aging behaviors and the tensile properties of Al-Mg-Si alloys have investigated by thermal analysis, microstructural characterizations and properties tests. The results demonstrate that the ultimate tensile strength and yield strength of Al-Mg-Si alloy can be increased by adding minor rare earth La. The effect mechanism of La has also been explored, it indicates that minor La enhances the strength of the Al-Mg-Si alloy by decreasing grain size and promoting the precipitation of (Mg, Si) phase. This study provides a way for manufacturing Al-Mg-Si alloys with excellent mechanical properties.
查看更多>>摘要：? 2022 Elsevier Inc.Based on TC21 alloy, the modified TC21G alloy with excellent comprehensive mechanical properties was designed. The influences of the double annealing process on microstructure and mechanical properties of TC21G alloy were investigated. The quantitative relationship between microstructure parameters, strength and impact toughness was established. Microstructural evolution with different double annealing conditions was characterized using SEM, TEM and EBSD. Results show that with reducing the cooling rate of first annealing, the size and content of the equiaxed and lamellar α phase both increased, and the width of the secondary α phase was increased, whereas the content of the fine acicular secondary α phase was decreased. Meanwhile, the fraction of high angle grain boundaries increased with reducing the cooling rate. The fine acicular secondary α phase was beneficial to improve the strength of TC21G alloy. Microstructural parameters of the equiaxed and lamellar α phase play a dominant role in improving ductility with reducing the cooling rate. Moreover, the crisscross lamellar and equiaxed α phase, the fraction of high angle grain boundaries are the main factors affecting impact toughness.
查看更多>>摘要：? 2022 Elsevier Inc.Porous Si3N4 ceramics are widely used materials but very difficult to join. In this work, we successfully ultrasonically soldered porous Si3N4 ceramic rapidly at a low temperature of 230 °C. The wetting and bonding mechanism at the ceramic/solder interface was studied. Results showed that the solder rapidly infiltrated the micro-channels of the ceramic during soldering, and high ultrasonic power contributed the sonocapillary distance. Zn and O acted as the main bonding elements. Bonding was realized by the formation of nanocrystalline and amorphous ZnOx region at the wetting interface. Rapid bonding was achieved due to the high liquid velocity, high temperature, and high pressure caused by the collapse of the cavitation bubbles.
查看更多>>摘要：? 2022 Elsevier Inc.A novel composite brazing alloy by introducing negative thermal expansion Y2Mo3O12 particles into AgCuTi alloy was developed to alleviate the residual stress of Cf/SiC-GH3536 joint. The negative thermal expansion behavior of Y2Mo3O12 material and its effects on the shear strength of brazed joints were investigated. The strong negative thermal expansion behavior of Y2Mo3O12 material greatly reduce the coefficients of thermal expansion of composite filler, which can greatly alleviate the residual stress of Cf/SiC-GH3536 joint. In addition, the interface structure has been greatly optimized, leading to enhanced bonding strength. The maximum shear strength of Cf/SiC-GH3536 joints reached ~42 MPa after added 3 wt% Y2Mo3O12, which was 1.6 times higher than that of original joints. This study shows that Y2Mo3O12 can maintain its strong negative expansion characteristics during the brazing process, which may provide a new idea to solve the hygroscopicity of Y2Mo3O12.
查看更多>>摘要：? 2022 Elsevier Inc.It has recently been established that vacancy loops of ~100 nm in maximum size could form in hydrogen pre-implanted α-Fe (Huang et al. Fusion Eng. Des., 2010). The formation temperature of these large loops is composition dependent, varying from ~500 °C in α-Fe, to ~450 °C in Fe[sbnd]Ni and ~ 620 °C in Fe[sbnd]Cr (Wan et al. J. Nucl. Mater., 2014; Du et al. Acta Metall. Sin., 2019). In this work, the effect of Mn addition upon vacancy loop formation has been investigated. Pure Fe and Fe-1.4 wt% Mn alloy specimens were irradiated with 30 keV H+ ions at room temperature. Radiation-induced loop production, size, population and nature were characterized based on diffraction contrast imaging using a combination of 1 MV high voltage electron microscope (HVEM) and 200 kV conventional transmission electron microscope (CTEM). Results of observation indicate that Mn addition gives rise to the increase of vacancy loop formation temperature in α-Fe, similar to the effect of Cr. A new criterion has been thus proposed, to classify the common alloying elements (Cr, Ni, Mn etc) found in Fe.
查看更多>>摘要：? 2022 Elsevier Inc.In the present study, the microstructural evolution and mechanical properties of T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite were studied. The results demonstrated that the grain refinement and eutectic Si modification effects of T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite are remarkable than that of T6 treated A356 alloy, and similar to that of T6 treated A356–0.3wt.%Ce alloy. More importantly, the in-situ reinforced (Al,Si)3(Ti,Ce) precipitates were found in T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite. TEM results and simulated diffraction pattern corresponding to the proposed crystal structure indicated that the (Al,Si)3(Ti,Ce) precipitates could be indexed consistently according to a body-centered tetragonal structure (I4/mmm space group, D022 type) with lattice parameters approximately of a = 0.519 nm and c = 0.859 nm. The existence of (Al,Si)3(Ti,Ce) precipitates resulted in the increase of strength due to the load bearing and coefficient of thermal expansion (CTE) mismatch strengthening. Besides, the fracture mode of the T6 treated A356–0.3wt.%Ce-1.5vol.%TiCN composite is a transgranular fracture. Compared with the T6 treated A356–0.3wt.%Ce alloys, A356–0.3wt.%Ce-1.5vol.%TiCN alloys showed better elongation, which is ascribed to the transformation of needle-like and hard Ce-rich phases distributing along with the eutectic Si to blocky and relatively soft (Al,Si)3(Ti,Ce) phases. The ultimate tensile strength (UTS) and the elongation (El) of the A356–0.3wt.%Ce-1.5vol.%TiCN composite were increased by 3.7% and 32.7% than that of the A356–0.3wt.%Ce alloy, respectively.
查看更多>>摘要：? 2022 Elsevier Inc.Electromagnetic forming is a high-speed forming method that can significantly improve the forming limit of metals. A high-density pulse current is induced on the workpiece during the forming process, however, research on the effects of the induced current on the material properties is lacking. This paper presents an experimental study designed to ensure the sheet is not deformed after discharge of the coil. Properties of rolled 5052 aluminum alloy treated by induced current were studied using mechanical testing, electron backscatter diffraction, and electron microscopy. The tensile strength, yield strength and elongation of the material increased by 6.9%, 8.7%, and 13.2%, respectively, after treatment using a voltage discharge of 6 kV, compared with the original rolled sheet. After an induced current is applied, dimples on the material are larger and more uniform, indicating better plasticity characteristics. Furthermore, the average grain size increases slightly and the subgrain content increases. The texture strength changes, as the Brass and Goss textures increase. The dislocation density is reduced, the distribution of dislocations becomes more uniform, and dislocation accumulation at grain boundaries weakens.
查看更多>>摘要：? 2022 Elsevier Inc.Low-temperature friction-stir welding (FSW) was successfully applied for the joining of Al-Mg-Mn alloy with an ultrafine-grained microstructure. The low-temperature conditions preserved fine-grained microstructure and nano-scale second-phase particles in the stir zone and thus provided nearly-100% joint efficiency of the produced welds. The deformation behavior of the welded joints was studied via the digital image correlation technique. The strengthening mechanisms of the base material and the stir zone material were examined.
查看更多>>摘要：? 2022 Elsevier Inc.In this work we develop a deep convolutional architecture to estimate the prior austenite structure from observed martensite electron backscatter diffraction micrographs. A novel data augmentation strategy randomizes the global reference coordinate system which makes it possible to train our model from only four micrographs. The model is much faster than algorithmic approaches and generalizes well when applied to micrographs of a different material. Empirical evidence suggests the efficacy of the model depends on the scale of the microstructure and receptive field of the vision model. This work demonstrates that modern computer vision approaches are well suited for capturing complex spatial-orientation patterns present in orientation imaging micrographs.
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