Microstructures and oxidation behavior of NiCrAlCoY-Al composite coatings on Ti-6Al-4V alloy substrate via high-energy mechanical alloying method

In the present work, NiCrAlCoY-Al gradient composite coatings were successfully fabricated on Ti-6Al-4V alloy substrate via high-energy mechanical alloying method. The microstructures and elemental and phase composition of the coatings have been studied. Effects of both NiCrAlCoY-Al powder ratio and milling time on the fabrication of composite coating were investigated. The NiCrAlCoY-Al weight ratio 65:35 was considered the optimal powder ratio to fabricate the coating at the selected milling parameters. The high-temperature cyclic oxidation tests were performed at 850 °C and 750 °C. The fabricated sample using 65:35 wt ratio and 4 h milling time showed the best oxidation resistance due to the low mass gain, rutile TiO2 undetected surface, and densified composite cross-section morphology. The decreased oxygen content of the oxidized cross-section line scanning results revealed the improvement of oxidation resistance. The oxidation process of the as-fabricated coating had been divided into five steps. Three protective Al2O3 oxide layers together with other alloy compounds could prevent the further diffusion of oxygen. The coating could enhance the oxidation resistance of the substrate.