Influence of Heat Treatments on Microstructure Evolution and Indentation Response of Equiatomic AlCrFeMoNbNi High-Entropy Alloy

Traditional IN-718 superalloy inspires the novel AlCrFeMoNbNi high-entropy alloy developed in this work. Major constituents of the IN-718 are selected in equiatomic proportions and processed via vacuum arc melting route. Alloy in the as-cast and heat-treated (1373 K for 24 h and 1373 K for 24 h + 1473 K for 48 h) conditions showed a multi-phase structure (BCC1, B2, Sigma, and BCC2) with high hardness of 11.94–9.08 GPa at indentation loads of 25–5000 g. Further, a significant indentation size effect (ISE) has been observed, which was confirmed by the Meyer’s power law. Strain gradient plasticity theory based on geometrically necessary dislocations, proposed by Nix and Gao, was adapted to understand the ISE. Further, depth-independent hardness values of 9.30 ± 0.9, 9.26 ± 0.9, and 10.41 ± 0.9 GPa and characteristic length scales of 0.52 ± 0.01, 0.53 ± 0.01, and 0.25 ± 0.02 µm were evaluated at different processing conditions in the current work. At 5000 g. load, K_IFT values (in MPa \(\sqrt m )\) $\sqrt{m})$ of 4.68, 6.61 and 6.29 were realized for as-cast, single heat-treated and double heat-treated conditions respectively.