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

The high melting point and thermal stability of MoWTaNbVTi_x 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 MoWTaNbVTi_x 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 MoWTaNbVTi_x manufactured by different PM approaches, pressureless sintering, hot isostatic pressing, and spark plasma sintering. A series of MoWTaNbVTi_x were manufactured using different PM manufacturing methods. Using intensive X-ray diffraction, microstructure, and elemental analysis, we reveal the formation of face-centered cubic (FCC) (TiTaNb)_0.53C_0.47 carbide and TiO_x oxide phase in the nonequiatomic body-centered cubic (BCC) MoWTaNbV matrix in MoWTaNbVTi_x. Interestingly, the liquid state sintering (LSS) yields a BCC_LSS matrix with a lattice parameter of 3.176 Å, differently than the solid state sintered (SSS) BCC_SSS matrix with a lattice parameter of 3.193 Å. The fraction of (TiTaNb)_0.53C_0.47 and TiO_x phases varies with titanium (Ti) composition and PM processing routes. Nickel (Ni), as the sintering activator, enhances Ti diffusion in the matrix. Also, the hardness of the MoWTaNbVTi_x varies nonlinearly in a range of ~ 602 to approximately 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 MoWTaNbVTi_x refractory high entropy alloys, reported in the literature.