Qiaoling Zheng

The pressure dependence of physical properties of (W2/3Ti1/3)3AlC2 and its counterpart W3AlC2 by first-principles calculations

First-principles calculations based on density functional theory (DFT) were used to investigate the mechanical properties, elastic anisotropy, electronic structure, optical properties and thermodynamic properties of a new quaternary MAX phase (W2/3Ti1/3)3AlC2 and its counterpart W3AlC2 under hydrostatic pressure. The results indicate that the volumetric shrinkage of (W2/3Ti1/3)3AlC2 is faster than that of axial shrinkage under hydrostatic pressure. The stress–strain method and Voigt–Reuss–Hill approximation were used to calculate elastic constants and moduli, respectively. These compounds are mechanically stable under hydrostatic pressure. Moreover, the moduli of (W2/3Ti1/3)3AlC2 and W3AlC2 increase with an increase in pressure. The anisotropic indexes and surface constructions of bulk and Young’s moduli were used to illustrate the mechanical anisotropy under hydrostatic pressure. Electronic structure and optical property of (W2/3Ti1/3)3AlC2 and W3AlC2 have also been discussed. The results of Debye temperature reveal that the covalent bonds among atoms in (W2/3Ti1/3)3AlC2 may be stronger than that of W3AlC2. The heat capacity, Cp–Cv, and thermal expansion coefficient of (W2/3Ti1/3)3AlC2 and W3AlC2 were discussed in the ranges of 0–30 GPa and 0–2000 K using quasi-harmonic Debye model considering the phonon effects.

On the Supplementation of Magnesium and Usage of Ultrasound Stirring for Fabricating In Situ TiB 2 /A356 Composites with Improved Mechanical Properties

Adding mixed K2TiF6-KBF4 salts into mechanical stirred molten A356 alloy (Al-7Si-0.3Mg) provides a simple method to fabricate in situ TiB2/A356 composites via salts-metal reaction. However, some issues, such as the loss of Mg element in A356 alloy and the clustering of TiB2 particles in the matrix, usually occur during the fabricating process. These issues easily result in the degradation of mechanical properties of composites. In this study, a quantitative analysis revealed that the Mg element was almost consumed after the reaction, and a thermodynamic analysis inferred that the loss of Mg resulted from the reaction between Mg and mixed salts. In order to fabricate in situ TiB2/A356 composites with high strength and good ductility, we proposed a developed approach that consisted of supplementing Mg and using ultrasound stirring during the fabricating process. The introduction of ultrasound into the melt could disperse TiB2 particles uniformly in the matrix, leading to more effective refinement of α-Al grains and modification of Si phase. Compared with the untreated A356, both the strength and ductility of the developed sample were improved significantly, and the coefficient of thermal expansion mismatch strengthening was found as the major contributor to the improvement in the yield strength.

Mechanical, tribological and oxidation resistance properties of Ni-based self-lubricating composite coatings at elevated temperature by APS

Abstract NiCrAlY-Mo-20Ag composite coating was fabricated by atmospheric plasma spraying. The influence of heat treatment on the mechanical properties, high temperature oxidation resistance properties and tribological properties of the coating were investigated. After 500°C heat treatment, the microstructure of the coating becomes more homogeneous and the amount of precipitated Y2O3 phase clearly increases. The micohardness and adhesive strength of the composite coating are effectively improved after heat treatment. The coating heat-treated at 500°C shows the highest micohardness and adhesive strength of 433.3 HV and 42.9 MPa as well as excellent lubricating properties over a wide range of temperature. Furthermore, the coating presents excellent oxidation resistance properties at 700°C and 800°C.

Effect of toughening Fe2B by the addition of tungsten on the wear resistance of Fe–B–C alloy

Abstract With an increase in the addition of W, the morphology and volume percentage of Fe2B show no obvious variation. Although an increase in the hardness of the alloy has a beneficial effect on improving wear resistance, toughening Fe2B by the addition of W has a more helpful role in the wear resistance of Fe–B–C alloy in this study. The weight loss of Fe–B–C alloy with the addition of 2.04 wt.% W can be decreased by more than 47 % of that of the alloy without added W.