Ultra-high strength WNbMoTaV high-entropy alloys with fine grain structure fabricated by powder metallurgical process

Abstract

An equi-atomic WNbMoTaV high entropy alloy (HEA) with a single body-centered cubic structure (BCC) was firstly fabricated by the powder metallurgical process of mechanical alloying (MA) and spark plasma sintering (SPS). Mechanical alloying behavior, microstructure and mechanical properties of the WNbMoTaV HEA were studied systematically. During MA, a single BCC phase was formed and the average particle size and crystallite size was refined to 1.83 µm and 66.1 nm, respectively, after 6 h of MA. Afterward, the as-milled powders were subsequently sintered in the temperature range of 1500–1700 °C. The microstructure of the sintered sample exhibits a few micrometer-scale grain size and a homogeneous BCC matrix with a small amount of oxide inclusion originated from oxidation during the powder metallurgical process. The bulk sample of the WNbMoTaV HEA sintered at 1500 °C shows an ultra-high compressive yield strength of 2612 MPa with a failure strain of 8.8% at room temperature, respectively. These mechanical properties of the WNbMoTaV HEA fabricated by the powder metallurgical process were attributed to the combined effects of grain boundary strengthening, substitutional solid solution strengthening, interstitial solid solution strengthening and Orowan strengthening by the oxide inclusions. Through a Hall-Petch analysis, the Hall-Petch coefficient of the WNbMoTaV HEA was derived. The WNbMoTaV HEA fabricated via the powder metallurgical process showed the best compressive yield strength when compared with the other reported refractory HEAs processed with arc-melting and casting.