Understanding the phase evolution and elemental distribution in MoWTaNbVTix manufactured via powder metallurgical approach

Abstract

The high melting point and thermal stability of MoWTaNbVTix refractory high entropy alloys have prompted their potential for harsh temperature structure application. A low-cost manufacturing strategy is key to realizing this promise. Powder metallurgy is known to be a cost-efficient manufacturing route for manufacturing refractory alloys. Elemental distribution and phases that form during manufacturing are crucial to realize the desired properties. However, the phase evolution and elemental distribution in MoWTaNbVTix refractory high entropy alloys manufactured via powder metallurgy (PM) have not been rationalized earlier. The present study focuses on the phase evolution and elemental distribution analysis in MoWTaNbVTix manufactured by different PM approaches, pressureless sintering, hot isostatic pressing, and spark plasma sintering. A series of MoWTaNbVTix were manufactured using different PM manufacturing methods. Using intensive X-ray diffraction, microstructure, and elemental analysis, we reveal the formation of an FCC (TiTaNb)0.53C0.47 carbide and TiOx oxide phase in the nonequiatomic BCC MoWTaNbV matrix in MoWTaNbVTix. Interestingly, the liquid phase sintering yields a BCC_LSS matrix with a lattice parameter of 3.176 Å, differently than the solid state sintered BCC_SSS matrix with a lattice parameter of 3.193 Å. The fraction of (TiTaNb)0.53C0.47 and TiOx phases varies with Ti composition and PM processing routes. Nickel, as the sintering activator, enhances Ti diffusion in the matrix. Also, the hardness of the MoWTaNbVTix varies nonlinearly in a range of ~ 602- ~911 Hv with the ratio of oxide and carbide fraction. The hardness obtained in the PM approach is significantly higher than that observed for cast MoWTaNbVTix refractory high entropy alloys, reported in the literature.