Effect of sintering temperature on microstructure and mechanical properties of MoNbVTa0.5Cr high-entropy alloys fabricated by powder metallurgy method

Abstract

To address the challenges posed by the high density and low plasticity at room temperature of traditional refractory high entropy alloys (RHEAs), the MoNbVTa0.5Cr RHEA was synthesized through a combination of mechanical alloying (MA) and spark plasma sintering (SPS) techniques. The effects of different sintering temperatures on the microstructure and mechanical properties of the alloy were systematically studied. The MoNbVTa0.5Cr RHEA milled up to 60 h was found to have a metastable dual-phase containing a major BCC (a = 3.1474 Å) and Nb-Ta (a = 3.3058 Å) phase. The sintered MoNbVTa0.5Cr RHEA was composed of BCC phase and a small amount of Ta2VO6 at different sintering temperatures. There were a lot of edge dislocations in the BCC matrix near the BCC/Ta2VO6 interface. With the increase of sintering temperature, the grain size of sintered MoNbVTa0.5Cr RHEA gradually increased, while the mechanical properties gradually decreased with the increase of sintering temperature. When the sintering temperature was 1500 °C, the grain size of the alloy was 2.33 μm, the yield strength was 2783 MPa, the compressive strength was 3346 MPa, and the fracture strain was 20.45 %, showing the best comprehensive properties. And the density of MoNbVTa0.5Cr RHEA was 9.11 g·cm−3 and 26 % lower than that of WNbMoTaV RHEA. The specific yield strength of MoNbVTa0.5Cr RHEA prepared in this research was 295.28 kPa·m3·kg−1, which was superior to most RHEAs reported so far. This sintered MoNbVTa0.5Cr RHEA showed an excellent room temperature compression performance, which can be attributed to the co-existence of BCC phase along with the minor Ta2VO6 phases. The high yield strength of MoNbVTa0.5Cr RHEA was mainly attributed to the substitutional solid solution strengthening of metal atoms, the interstitial solid solution strengthening of O atoms and the grain boundary strengthening of ultrafine grains, with contributions to yield strength of 41 %, 28 %, and 24 %, respectively.