A novel refractory WMoVCrTa high-entropy alloy possessing fine combination of compressive stress-strain and high hardness properties

摘要

Refractory high-entropy alloys (HEAs) possess outstanding mechanical strength at room and high temperature but lack the room temperature ductility. A novel refractory equiatomic powder combination of WMoVCrTa was selected and verified for the feasibility of formation of solid solutions or else bulk metallic glasses (BMGs) in the alloy based on the Guo et al.'s criteria and mismatch entropy criterion. The powder combination satisfies the above two criteria to crystallize in solid solution phases and inhibit the BMGs. Mechanical alloying characteristics of the powder mixture were determined. The particle size of the powder mixture decreased continuously during initial milling and later increased after 32 h of mechanical alloying. A homogeneous mixture was obtained after milling for 64 h. Crystallite sizes of the constituent elements in the powder mixture decreased continuously on progressive milling. A nanocrystalline powder was obtained by mechanical alloying. The powder milled for 64 h revealed a major BCC1, a minor BCC2 and small unknown phases. The lattice parameters of those BCC1 and BCC2 phases are 3.16 angstrom and 2.88 angstrom respectively. The alloy ingots were fabricated from the milled powder by vacuum arc melting technique followed by heat treatment. The ingot crystallizes in three phases such as a major BCC1, a minor BCC2 and a minor laves phase. The lattice parameters of these BCC1 and BCC2 phases are 3.05 angstrom and 2.85 angstrom respectively. Thereby, the BCC1 lattice of the milled powder contracts slightly after ingot fabrication. A fine combination of compressive stress and strain of 995 MPa and 6.2% respectively was achieved by the alloy at room temperature. Vickers hardness of the alloy was as high as 773 +/- 20HV0.5. The density of the alloy was 11.52 g/cm(3). The combination of excellent room temperature stress-strain and high hardness properties can enable the refractory HEA as a potential candidate for structural applications. (c) 2020 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.