Annealing treatment's impact on the microstructure and mechanical properties of HVOF-sprayed high-entropy alloy coatings with AlxCoCrFeNi composition (x = 0.4, 0.7, 1.0).

In this study, the High Velocity Oxygen Fuel (HVOF) technology was utilized to fabricate HEA coatings composed of Al x CoCrFeNi (x = 0.4, 0.7, 1.0), followed by subsequent vacuum annealing conducted at temperatures spanning 500, 700, 900, and 1100 ℃. The microstructure, phase compositions and mechanical properties of HVOF-sprayed Al x CoCrFeNi HEA coatings before and after vacuum annealing were analyzed. Our findings indicate that the HVOF-sprayed Al x CoCrFeNi HEA coatings demonstrate a single solid solution phase (either FCC or BCC). As the Al content rises, the phase structure of the HEA coating shifts from FCC to BCC, resulting in increased hardness, H/E ratio, and H3/E2 ratio. After undergoing vacuum annealing at 500℃, the Al x CoCrFeNi HEA coatings retain the identical microstructure and phase composition as the as-sprayed state. With increasing annealing temperature, the BCC phase to FCC phase transformation occurs and the microstructure coarsens. After vacuum annealing at 500℃, the hardness, H/E and H3/E2 values of the coatings are most significantly enhanced due to the grain boundary dislocation source strengthening. At 700 and 900℃, the mechanical properties of the coatings are also improved as a result of the existence of the σ phase. However, at 1100℃, the mechanical properties of the coatings decline due to phase transformation and grain coarsen. This indicates that HVOF technology and appropriate annealing process may be a new strategy for designing high-performance HEA coatings, which has potential applications in aerospace, geological drilling, marine ships and other fields. • Appropriate annealing post-treatment might be a novel strategy for designing AlxCoCrFeNi HEA coatings with high performance. [ABSTRACT FROM AUTHOR]