In situ synthesis of TiN/Ti3Al intermetallic matrix composite coatings on Ti6Al4V alloy

Abstract

The aim of this paper was to develop an in situ method to synthesize the TiN reinforced Ti3Al intermetallic matrix composite (IMC) coatings on Ti6Al4V alloy. The method was divided into two steps, namely depositing pure Al coating on Ti6Al4V substrate by using plasma spraying, and laser nitriding of Al coating in nitrogen atmosphere. The microstructure and mechanical properties of TiN/Ti3Al IMC coatings synthesized at different laser scanning speeds (LSSs) in laser nitriding were investigated. Results showed that the crack- and pore-free IMC coatings can be made through the proposed method. However, the morphologies of TiN dendrites and mechanical properties of coatings were strongly dependent on LSS used in nitriding. With decreasing the LSS, the amount and density of TiN phase in the coating increased, leading to the increment of microhardness and elastic modulus and the decrement of fracture toughness of coating. When the LSS was extremely high (i.e., 600mm/min), only a thin TiN/Ti3Al layer with thickness around of 100μm was formed near the coating surface.