Oxidation behavior of Cr-AlSi12 composite coatings on Ti-6Al-4V alloy substrate fabricated via high-energy mechanical alloying method

Abstract

In this paper, to protect Ti-6Al-4V alloy from oxidation, the Cr-AlSi12 composite coatings were successfully prepared on Ti-6Al-4V substrate by high-energy mechanical alloying method. The effects of powder weight ratio and milling duration on the fabrication of the coatings were studied. The addition of AlSi12 restricted the formation of microholes and the microstructure was homogenized at suitable milling time. The high-temperature oxidation resistance of the coatings was evaluated by oxidation mass gain. The coating consists of two layers, one is the inner layer with large particles of Cr and the other is the outer layer with highly homogenized structure. The formation process of the coatings was studied. The as-prepared coating could significantly improve oxidation resistance of the substrates, which is mainly due to the following two points. First, the formation of Al2O3 oxide layers, AlCr and CrSi intermetallic phases inside the coating were favourable to densification of the coating, thereby preventing the diffusion of oxygen. Second, a thin Si-rich layer formed at the coating-substrate interface could effectively prevent further diffusion of oxygen. The coated samples prepared using weight ratio 60:40 and milling time of 5 h, which exhibited lowest oxidation mass gain value and excellent microstructure, was the optimum parameter.