Ti₃Al/TiN Composite Coatings Fabricated By Laser Surface Alloying And Their Properties

Aiming at the problem of the laser alloying technology, Ti3Al/TiN composite coatings were prepared at the surface of the titanium alloy substrate through the method of adding alloy elements and optimizing the process parameters. This composite coating had excellent performance and this method effectively solved the problem of cracking in traditional laser nitriding. The microstructure and mechanical properties of the composite coating were investigate by using scanning electron microscopy, X-ray diffraction, energy dispersive spectrdmeter and through measurements of microhardness, elastic modulus and fracture toughness to clarify the effect of processing parameters. The main conclusions were as follows:(1) The Ti3Al/TiN composite coatings were prepared by using a two-step synthesis method, namely deposition of Al coating on the Ti substrate and then laser nitriding. It was found that the distributions of Ti3Al phase and TiN phase in coating were uniform. The micro-cracks and pores cannot be found in the coating。(2) This composite coating was mainly composited of nitride phase and the Ti-Al intermetallic phase, the laser power and the laser scanning speed had significant influences on the developing of the amount and distribution of nitride dendrite. However, the effect of flow rate of nitrogen gas in laser nitriding on the microstructure of coating was not obvious. The uniform distribution of the phases in coating can be achieved through optimization of processing parameters.(3) The microhardness of the Ti3Al/TiN composite coating was obviously high by comparing with that of substrate. The amount and distribution of TiN phase had an important influence on the hardness of coating. Generally, the microhardness of the composite coating increased with increasing the content of TiN phase.(4) The elastic modulus and fracture toughness of the composite coatings were measured by using indentation method. It was found that the elastic modulus of the coating was higher than that of substrate. However, the fracture toughness of coating was influenced by the content of nitride phase. Generally, the fracture toughness decreased as the content of nitride phase increased.