The influence of heat treatment processes on microstructure and properties of in-situ synthesized titanium matrix composite coatings

This study fabricated BN-Ti composite coatings via laser cladding technology, with a focus on investigating the influence of different heat treatment temperatures (750∼1050 °C) on the microstructure and hardness of the clad layers. The as-deposited coating without heat treatment primarily exhibited irregular TiN equiaxed grains with limited TiB reinforcing phase precipitation. When the heat treatment temperature increased to 750 °C, the TiN particles became more uniform and developed regular morphologies, while a small amount of needle-like TiB phase began to precipitate. At 850 °C, the TiN particles grew further, and the needle-like TiB phase increased significantly. After 950 °C heat treatment, the precipitation of reinforcing phases reached its optimal state, forming a fine network structure between TiN and TiB phases, corresponding to peak coating hardness. However, when the temperature was further raised to 1050 °C, noticeable coarsening occurred, accompanied by secondary coarsening of TiN, reduction in TiB phase quantity, and disappearance of the network structure, leading to significant hardness degradation. The 950 °C annealing regime is shown to produce an ideal grain architecture and enhanced property matrix in BN-Ti laser-deposited coatings, offering key insights for thermal post-processing protocol development.