Effect of Annealing Treatment on Microstructure, Mechanical Properties and Oxidation Resistance of SiCp/Al Coating Synthesized on Ti–6Al–4 V Alloy Substrate by Mechanical Alloying Method

Abstract

An Al–SiC coating was synthesized on Ti–6Al–4 V alloy substrate using the mechanical alloying method. The effects of annealing treatment on the microstructure, the microhardness, the friction and wear resistance and the high-temperature oxidation resistance of the coating were investigated. The results showed that the coating had a composite structure in which the reinforcing SiC particles were evenly dispersed in the Al matrix. Both the surface microhardness and the wear resistance of the substrate improved because of the as-synthesized coating. The oxidation resistance was enhanced because of the formation of an Al3Ti layer and a Ti5Si3-rich layer in the coating during oxidation. Specifically, the coating formed a tri-layer structure during thermal exposure due to the reaction in the coating and interdiffusion between the coating and the substrate. The outer layer had a complex structure, which was comprised of the Al–Si alloy as the matrix and the unevenly distributed SiC and Al4C3. This layer had low microhardness and tended to flake in both friction and oxidation processes. The inner layer was an Al3Ti layer, which had high microhardness and favorable wear resistance, and could protect the substrate from severe oxidation at elevated temperature. A Ti5Si3-rich interlayer between the inner layer and the substrate formed in the initial annealing process and could further retard the inward diffusion of oxygen during oxidation.