Mechanical properties and reciprocating sliding tribological behaviors of γ-TiAl substrate and plasma-based Mo–Si–Ti coating

Abstract

Plasma Mo–Si–Ti coating including the (Ti, Mo)5Si3, MoSi2 and TiSi was prepared on γ-TiAl surface to improve the wear resistance. The coating had 12-μm deposition layer and 5-μm diffusion layer, as well as gradual decrease of grain size from substrate to coating, providing gradient structure and high fracture toughness. Hardness (H), elasticity modulus (E), H/E and H3/E2 values of substrate and coating were 8.4 and 19.6 GPa, 167.2 and 251.8 GPa, 0.050 and 0.078, and 0.021 and 0.119 GPa, indicating that coating had high hardness, resistance to plastic deformation and load bearing capacity. During friction, both the substrate and coating showed abrasive and oxidative wear. The substrate flaked off in the form of large wear debris, causing the high wear rate. However, oxide film and compacted layer of fine debris made the wear rates of substrate to decrease as the load increased. The coating released most of external stress in the form of elastic work, showing high load-bearing capacity. High fracture toughness inhibited the generation of cracks and reduced the spallation of coating. Moreover, fine grains promoted the generation of oxide film on coating surface and improved the adhesion between oxide film and coating. Meanwhile, the presence of oxide film resulted in a reduction of wear rate as the load increased. The excellent nanomechanical properties and fracture toughness reduced the fracture of coating and reduced the specific wear rate of γ-TiAl by about 98%, which could effectively improve the wear resistance of γ-TiAl at room temperature.

Keywords

• γ-TiAl
• Mo–Si–Ti gradient coating
• Nanoindentation
• Wear mechanism