A fine-grained NbMoTaWVCr refractory high-entropy alloy with ultra-high strength: Microstructural evolution and mechanical properties

Abstract

Mechanically alloyed (MA) NbMoTaWVCr refractory high-entropy alloy (HEA) powders were sintered by spark plasma sintering (SPS) at temperatures of 1400–1700 °C. The microstructural evolution and mechanical properties of sintered HEAs were subsequently investigated. During the MA process, only a supersaturated body-centered cubic (BCC) structured solid solution was formed. However, C15 Laves phase (Cr,V)2(Ta,Nb) and Ta2VO6 particles were precipitated from the disordered BCC phase during the sintering process at temperatures ≤1500 °C. When the sintering temperature increased to 1600 °C, the Laves phase was transferred to C14 structure and its volume fraction was dramatically reduced. The plasticity of the refractory HEA was strongly affected by the fraction, size and distribution of Laves phase and oxide particles. The NbMoTaWVCr alloy sintered at 1500 °C obtained an excellent combination of yield strength (3416 MPa) and failure plasticity (5.3%) at room temperature. The extraordinary high strength of this HEA could be dominantly attributed to the grain boundary strengthening from the micron-sized BCC phase (1.24 μm), interstitial solid solution strengthening from O in the matrix and the inherent solid solution strengthening in the multi-principal element NbMoTaWVCr alloy.