Mechanical properties of high-entropy alloys (HEAs) have received significant attention, while there are still attempts to find new strategies to further improve their properties. In this study, to produce an ultrahard HEA, an FCC carbide was introduced in a BCC-based AlTiFeCoNi alloy by the assistance of CALPHAD thermodynamic calculations. The alloy was synthesized by arc melting and processed by severe plastic deformation via the high-pressure torsion (HPT) method to generate defects. The material showed nanograin formation, dislocation accumulation, carbide fragmentation, L21 → BCC ordered-to-disordered phase transformation, and accordingly an ultrahigh hardness of 950 Hv after HPT processing.
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