Effect of nitriding treatment on microstructure, mechanical property and wear mechanisms of AlxCoCrFeNi high entropy alloy coatings prepared by cold spraying

In this study, the Al_xCoCrFeNi high entropy alloy coatings are firstly prepared on the surface of the substrate by cold spraying technology, followed by nitriding treatment. This study investigates the effects of nitriding on the microstructure, mechanical properties and wear mechanisms of Al_xCoCrFeNi high entropy alloy coatings at different temperatures. The results reveal that increasing Al content causes the phase structure transition from FCC phase to BCC phase, correlating with enhanced mechanical properties and tribological performances. Nitriding further promotes these properties by introducing FCC phases and various nitrides. Among the tests, the Al_0.7CoCrFeNi high entropy alloy coating exhibits the highest microhardness and best wear resistance after nitriding. The wear mechanisms of Al_xCoCrFeNi high entropy alloy coatings vary with different temperatures, the detail as follows: at 25 °C and 100 °C, the coatings mainly experience fatigue, spalling, and oxidation wear. As the temperature increases to 300 °C the wear mechanisms transition to abrasive wear and adhesive wear, and at 500 °C, it mainly the plastic deformation. In contrast, the nitriding Al_xCoCrFeNi high entropy alloy coatings exhibit abrasive wear at 25 °C, which shifts to fatigue and oxidation wear as the temperature increases.