Microstructure, Hardness, and Corrosion-Wear Behavior of Nitrided Al <i>x</i> CoCrFeNi High-Entropy Alloy Coatings Deposited by Cold Spraying

Abstract In this study, AlxCoCrFeNi high-entropy alloy coatings were prepared on the surface of a common drilling tool material substrate of 4330V steel using cold spraying technology, followed by nitriding treatment. The microstructure, hardness, corrosion properties, and corrosion-wear mechanisms were investigated with different loads on AlxCoCrFeNi high-entropy alloy coatings. The results showed that the phase structure of the Al0.4CoCrFeNi high-entropy alloy coating was face-centered cubic (FCC), while that of the Al0.7CoCrFeNi high-entropy alloy coating was body-centered cubic (BCC). The nitriding treatment promoted the formation of nitride phases for the Al0.4CoCrFeNi and Al0.7CoCrFeNi high-entropy alloy coatings, thereby enhancing their hardness. The corrosion resistance of the Al0.7CoCrFeNi was better than that of the Al0.4CoCrFeNi high-entropy alloy coating, and the nitriding treatment consumed some of the Al, which reduced the corrosion resistance of the coatings. Regarding the corrosion-wear performance, the Al0.4CoCrFeNi high-entropy alloy coating exhibited a lower coefficient of friction and a lower corrosion-wear-rate than the Al0.7CoCrFeNi high-entropy alloy coating, and the nitriding treatment further reduced those. The main wear mechanisms for the Al0.4CoCrFeNi and Al0.7CoCrFeNi high-entropy alloy coatings before and after nitriding treatment included abrasive wear, oxidative wear, and pitting corrosion with different loads. After the nitriding treatment, the corrosion-wear reaction of the Al0.4CoCrFeNi and Al0.7CoCrFeNi high-entropy alloy coatings was weakened. However, as the load increased, the corrosive wear reactions in the coatings became more intense.