Microstructure and mechanical properties of ultra-fine grained MoNbTaTiV refractory high-entropy alloy fabricated by spark plasma sintering

Abstract

The MoNbTaTiV refractory high-entropy alloy (RHEA) with ultra-fine grains and homogeneous microstructure was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). The microstructural evolutions, mechanical properties and strengthening mechanisms of the alloys were systematically investigated. The nanocrystalline mechanically alloyed powders with simple body-centered cubic (BCC) phase were obtained after 40 h MA process. Afterward, the powders were sintered using SPS in the temperature range from 1500 °C to 1700 °C. The bulk alloys were consisted of submicron scale BCC matrix and face-centered cubic (FCC) precipitation phases. The bulk alloy sintered at 1600 °C had an average grain size of 0.58 μm and an FCC precipitation phase of 0.18 μm, exhibiting outstanding micro-hardness of 542 HV, compressive yield strength of 2208 MPa, fracture strength of 3238 MPa and acceptable plastic strain of 24.9% at room temperature. The enhanced mechanical properties of the MoNbTaTiV RHEA fabricated by MA and SPS were mainly attributed to the grain boundary strengthening and the interstitial solid solution strengthening. It is expectable that the MA and SPS processes are the promising methods to synthesize ultra-fine grains and homogenous microstructural RHEA with excellent mechanical properties.