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We studied the microstructure evolution of Mg-4Y-3Nd-2Sm-0.5Zr alloy by quasi-in-situ electron backscatter diffraction (EBSD) along with several strains under compression tests, which provided direct evidence for the influence of different twin-twin geometric structure on the twinning behavior. The results showed that the mechanical properties of the alloy were higher than traditional magnesium alloys (the maximum compressive strength reaches 402.5 MPa) due to the strengthening effect of Sm and Nd elements addition on solution strengthening, precipitation strengthening, and grain refinement. Combined with the quasi-in-situ EBSD technique, two different twin-twin geometric structures, ‘parallel structure’ and ‘cross structure’, were observed directly in the alloy. In the later stage of deformation, for ‘parallel structure’, residual stress and a large number of dislocations mainly existed in the twin boundary and tip position. For the ‘cross structure’, there was a lot of dislocation density in the interior of twins after fusion. The twin growth rate of ‘parallel structure’ was much faster than that of ‘cross structure’ because the stress of twins was mainly concentrated on the tip of twin. When the movement for the tip of twin was blocked, the growth rate of twin would be obviously decreased. Moreover, the ‘cross structure’ was easy to produce closed space. Due to the constraints of surrounding twins, the confined space was easy to stress concentration, thus inhibiting the growth of twins. At the same time, the ‘cross structure’ of twins needed a more external force to continue to deform, which also served as a strengthening structure.

The recent progress and potential challenges of element-doped VO2 are systematically reviewed. The roles of element doping in modulating the properties of VO2 are discussed in particular, aiming to inspire the current research.

In order to overcome the interfacial incompatibility of carbon fiber reinforced magnesium matrix (Cf/Mg) composites, a double-layer interface (ZrO2–MgO) is designed in this work. Carbon fiber was modified with ZrO2 coating by sol-gel process. Microstructural examination reveals that MgO layer forms on the surface of ZrO2 coating by ZrO2 reacting with Mg during the composite fabrication. Such double-layer interface could inhibit Al4C3 and hence prevent fiber damage. Meanwhile, the wettability was improved for the reaction between ZrO2 and Mg. Thus the tensile strength of ZrO2-Cf/AZ91D composite was 68.0% higher than that of the unmodified one. Due to the fiber bundle pull-out, debonding and crack deflection, the toughness of Cf/Mg composite with double-layer interface is increased simultaneously.

Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures (350–500 °C), strain rates (0.01–5 s−1), and strains (0.2, 0.4, and 0.8). A strong dynamic softening is observed in all stress-strain curves, even at higher strain rates (1 and 5 s−1) due to an adiabatic heating effect. Various stress-strain curves are applied to construct a processing map and develop an Arrhenius-type constitutive equation. With the prediction of the processing map, an optimal processing domain has been determined to be the temperature range 450–500 °C and strain rate range 0.01–0.1 s−1 at a strain of 0.8. The volume fraction of DRX grains is the largest in the corresponding domain of high temperature and low strain rate. For the effect of TMP parameters on the dynamic restoration, the discontinuous dynamic recrystallization (DDRX) and continuous DRX (CDRX) synergistic effect occur throughout the whole process at high temperature and high strain rate. In terms of high temperature and low strain rate, DDRX characteristics at a low strain and then the DDRX + CDRX synergistic effect is observed at a higher strain. Although the DRX process is weak at low temperature and low strain rate, deformation twins have occurred and provided nucleation sites for DRX grains.

A HfC-TaC composite coating was prepared on SiC-coated C/C composites by supersonic atmosphere plasma spraying (SAPS) to improve their ablation resistance. The ablation resistance was evaluated under oxyacetylene torch with heat flux of 2.38 MW/m2 and 4.18 MW/m2 respectively, and the effect of TaC on microstructure and phase composition of the coating was investigated. Results showed that TaC-modified HfC coating exhibited good ablation resistance under the torch with heat flux of 2.38 MW/m2 and its mass and linear ablation rates were -0.35 mg/s and -1.05 μm/s separately, which is ascribed to the formation of continuous oxide film including phases like Hf6Ta2O17 and Ta2O5. Crack propagation in the coating was inhibited due to the phase transition restriction of HfO2 by Ta2O5, and cracks and holes in the oxide layer could be repaired by molten Ta2O5 and Hf6Ta2O17. However, the occurrence of ablation crater on the surface of HfC-TaC coating is mainly attributed to the unsatisfactory scouring resistance of the oxide film under heat flux of 4.18 MW/m2.

A modified random fiber removal algorithm is proposed to numerically study transverse elastic properties of unidirectional carbon fiber reinforced pyrolytic carbon (C/C) composites. This method can efficiently generate the Representative Volume Element (RVE) of composites with random distribution fibers. On the basis of the numerical homogenization strategy, the effect of interphase between carbon fiber and pyrolytic carbon on the mechanical behaviors of unidirectional C/C composites are investigated. Meanwhile, periodic boundary conditions and linear elastic constitutive materials are taken into account. For validation, numerical calculations are compared with these obtained by atomic force microscopy (AFM) tests, which shows that more accurate results will be pursued when the interphases are considered. In addition, the influences of interphase parameters including the thickness, modulus, and Poisson’s ratio, on the effective transverse behavior of unidirectional C/C composites are studied numerically.The results demonstrate that the effective transverse properties of unidirectional C/C composites are mainly determined by the interphase modulus and independent of the interphase Poisson’s ratio. If the interphase thickness (less than 140 nm) of unidirectional C/C composites are very small, the modulus of interphase beyond 8 GPa makes little effect on the effective transverse properties.

The room-temperature ductility of the Mg alloys is closely related to the deformation behavior of the twin. However, there are currently no effective criteria that can accurately predict in which grains twins will nucleate during plastic deformation. With the rapid development of artificial intelligence technology, the applications of machine learning in the microstructure design and predictions have become the highlight. In the present study, a novel Mg-4Y-3Nd-2Sm-0.5 Zr alloy is prepared so as to explore the twin nucleation behavior of Mg alloys by combining machine learning along with electron backscattered diffraction (EBSD) techniques. At a true strain of 0.05, twins are found in 68 grains of the 297 grains which are counted from the initial microstructure. Eight features that may affect the twin nucleation are selected, including the grain diameter, the number of neighboring grains, the Schmid factor, and so on. Furthermore, the relevant importance of eight features on twin nuclei are also sorted; the grain diameter of original grains and the Schmid factor of the tensile twins have the greatest influence on the twin nucleation. Three machine learning algorithms including XGBoost, ANN, and the proposed relevance based ensemble scheme are used to model the prediction of the twin nucleation. The proposed relevance based ensemble scheme achieved an AUC score of 0.880, which is higher than that of the ANN (0.879) and XGBoost (0.756). A better ROC and PR curve also validate the feasibility of the proposed scheme.