Effects of Solution Treatment on the Microstructure and Properties of Al0.4Co0.5V0.2FeNi High-Entropy Alloys

This work explores V-alloyed Al0.4Co0.5V0.2FeNi high-entropy alloys that are solution-treated at 1000–1200 °C for five hours and water-quenched. Solidification of this high-entropy alloy follows the sequence face-centered cubic (FCC) → ordered L12 → body-centered cubic (BCC) → ordered B2. All treated alloys maintain dual FCC–BCC-B2 microstructures, with temperature altering only morphological features. At 1000 and 1100 °C, coherent spinodal decomposition takes place in FCC matrices to form rodlike precipitates with 20.3% lattice misfit; meanwhile, Ostwald ripening lengthens the precipitates from 1.41 to 2.11 μm. Spinodal decomposition is inhibited at 1200 °C, which is accompanied by coarsening and granulation of B2-ordered BCC grains. Slow atomic diffusion prevents recrystallization even above 0.4Tm. Solution heat treatment dissolves the B2 phases to generate supersaturated solutions stronger than the as-cast counterparts. Elevated solution temperatures reduce hardness (243–190 MPa) and tensile strength (919–839 MPa) but boost elongation (26–35%). Fractures display mixed dimple-cleavage features. Overall, a five-hour solution treatment at 1100 °C plus water quenching delivers balanced strength (851 MPa) and ductility (33%), serving as the optimal heat treatment for this alloy.