Linking novel processing, thermo-mechanical response and high-temperature oxidation in refractory high-entropy alloy via a multiscale computational-experimental approach

A novel synthesis route was studied to prepare aluminium-containing refractory high-entropy alloys. The approach involves co-reduction of constituent refractory metal oxides using aluminium in predetermined proportions. For demonstration, a Ta 19.3 Mo 23.4 Nb 20.1 Cr 16.7 Al 20.4 alloy (molar percentages) was designed using FactSage thermochemical databases based on heat and mass balance calculations. The as-reduced material was sequentially processed by arc-melting, annealing and deformation at 1250 °C and 1400 °C. The alloy comprised of two body-centred cubic phases: a Mo-rich phase and a Cr(Al,Nb)-based solid solution with metastable C14-Laves phase. The elastic moduli of these two phases were predicted using density functional theory simulations coupled with finite element modelling and experimentally correlated to nanoindentation results. Hot deformation produced synchronous grain refinement in both derived ordered B2 phases. Transmission electron microscopy revealed that these phases accommodated deformation through dislocation cells and antiphase boundaries, promoting dynamic recrystallisation, whereas the C14-Laves grains exhibited dense parallel stacking faults transitioning to the C15-Laves phase. Oxidation at 850 °C for 50 h showed marginal weight-gain vis-à-vis a similar composition produced by the arc-melting route, forming protective Al 2 O 3 and NbCrO 4 oxide layers. This work establishes a cost-effective and scalable process for this class of materials offering microstructures and properties comparable to conventionally adopted techniques.