Effects of annealing treatment and pre-refinement of raw material on microstructures and properties of mechanically alloyed Cr–Al composite coatings on Ti–6Al–4V alloy

• Mechanical alloying method was applied to form Cr–Al coatings.
• Annealing treatment was applied to improve the properties of the coating.
• Coating with highly homogenized structure was prepared with refined Cr particles.
• Wear and oxidation resistance of the coatings were investigated.
• The coating could effectively protect the substrate.

A high-energy planetary ball mill was applied to prepare Cr–Al composite coatings on Ti–6Al–4V alloy substrate. The coatings were fabricated using the mixture of pure Al and Cr powders. Effects of annealing treatment and pre-refinement of raw Cr particles on the coatings were discussed through the comparison of the microstructure, phase compositions, microhardness, friction and wear property and oxidation resistance of the as-synthesized coatings. The results indicated that the pre-refinement of the Cr particles was conductive to the improvement of the microstructure, the mechanical and oxidation properties of the coating. The annealing treatment at 800 °C could promote the alloying in the coating. After annealing treatment, the main compositions of the coatings prepared using coarse Cr particles were AlCr2 and Al8Cr5, and the coatings prepared with refined Cr particles mainly included Al8Cr5 and Cr. The annealing treatment favored the improvement of the coating microhardness and wear resistance. The annealing treatment would result in the formation of microdefects in the coating fabricated with coarse Cr particles but the formation of highly homogenized microstructure in the coating fabricated with refine Cr particles. The oxidation behavior of the coating prepared with refined Cr particles was improved after annealing treatment.