Xingwang Cheng

The Microstructure and Mechanical Properties of Refractory High-Entropy Alloys with High Plasticity

Refractory high-entropy alloys (RHEAs) are promising materials used at high temperature, but their low plasticity restricts their application. Based on the valence electron concentration (VEC) principle, four kinds of RHEAs (ZrTiHfV0.5Nb0.5, Zr2.0TiHfVNb2.0, ZrTiHfNb0.5Mo0.5, and ZrTiHfNb0.5Ta0.5) are designed (VEC < 4.5). The experimental results show that the plasticity of these alloys was greatly improved: the static compressive strain was higher than 50% at room temperature (RT), and some elongations were produced in the tensile process. Moreover, the microstructure and phase composition are discussed in detail. The addition of Nb, Mo, and Ta contributed to the high-temperature strength. Finally, the dynamic mechanical properties of these RHEAs with coordination between strength and plasticity are investigated.

Preparation and Dynamic Mechanical Properties at Elevated Temperatures of a Tungsten/Glass Composite

Experiments were conducted to prepare a borosilicate glass matrix composite containing 50xa0vol.% tungsten and examine its dynamic compressive behavior at elevated temperatures in the range of 450-775xa0°C. The results show that the homogenous microstructure of the tungsten/glass composite with relative density of ~xa097% can be obtained by hot-pressing sintering at 800xa0°C for 1xa0h under pressure of 30xa0MPa. Dynamic compressive testing was carried out by a separate Hopkinson pressure bar system with a synchronous device. The results show that the peak stress decreases and the composite transforms from brittle to ductile in nature with testing temperature increasing from 450 to 750xa0°C. The brittle–ductile transition temperature is about 500xa0°C. Over 775xa0°C, the composite loses load-bearing capacity totally because of the excessive softening of the glass phase. In addition, the deformation and failure mechanism were analyzed.

Study on Preparation and Corrosion Resistance of Graphene-Ni 35 Co 30 Cu 20 Fe 15 High Entropy Alloy Composites

The graphene/Ni 35 Co 30 Cu 20 Fe 15 high entropy alloy composites were successfully prepared by ball milling and spark plasma sintering (SPS) methods. The microstructures and structures of graphene and composites were measured by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The hardness and corrosion resistance of the composites were tested by Vivtorinox hardness tester and chemical workstation. The results showed that the homogeneous distribution of graphene in the composites can be achieved by ball milling, and the original structure of graphene was not destroyed. The addition of graphene improved the hardness and corrosion resistance of high entropy alloy composites. Compared with the Ni 35 Co 30 Cu 20 Fe 15 high entropy alloy, the hardness of the high entropy alloy with 0.3 wt.% Graphene increased from 255HV to 310HV. The addition of graphene increased the corrosion potential of the composite in 3.5% NaCl solution from -0.5V to -0.2V and the corrosion current density from 2×10 -5 A/cm 2 reduced to 8×10 -6 A/cm 2 , which greatly improved the corrosion resistance of the material.