Modifying strengthening mechanisms in MoNbZrTiV refractory high-entropy alloy particles through different mechanical alloying routes

MoNbZrTiV refractory high-entropy alloy (RHEA) particles are developed using conventional and sequential mechanical alloying (MA) routes at varying milling times. The conventional MA route employed a single-step milling of Mo, Nb, Zr, Ti, and V. In contrast, the sequential MA route started with the milling of MoNbZr, followed by a stepwise addition of Ti and V at specific milling intervals. Increased interdiffusion zones, resulting from finer lamellar structure formation, lead to ‘chemical homogenization’ and are observed with increasing milling time. After 24 h of milling, comparable experimental hardness values are recorded, 7.62 GPa for conventionally milled and 7.48 GPa for sequentially milled particles, primarily due to the evolution of three body-centered cubic (BCC) phases, corresponding to Nb-, Zr-, and V-rich phase structures in both MA routes. Further investigations suggest a distinct difference in the calculated dislocation densities, phase volume fractions, and the related phase strengthening mechanisms between the two routes as a function of milling time. Conventionally milled particles exhibit dislocation strengthening, whereas sequentially milled particles reveal possible dislocation motion impediment associated with V-V split interstitial defect formation. Further, the thermodynamic parameters (complemented with calculated power and energy) provided valuable predictions for the multi-phase solid solution formation.