In-situ TiN/Ti₃Al Composite Coating Generation Technique On Surface Of Titanium Alloy And Performance Study

In this study,TiN/Ti3Al composite coatings with excellent performance were produced successfully on titanium alloy by using laser gas nitriding and synchronous feeding power technology.The micro-morphology,micro-hardness,physical phase composition and the high-temperature erosion resistance were investigated detailedly.In order to obtain more excellent coating,ultrasonic vibration platform was applied into the preparation of the coatings.The new coating was compared with the previous coating in micro-morphology,micro-hardness and surface residual stress.The results show that:(1)TiN/Ti3A1 composite coatings with excellent performance were produced successfully.Defects such as cracks and porosities were not observed in the composite coating,and good metallurgical combination between matrix and composite coating formed.(2)The microstructure of the composite coating showed that:the composite coating was mainly composed by dendrite-shape or mash-shape phase and intermetallic compound.With the XRD we found that the dendrite-shape or mash-shape phase was TiN,the intermetallic compound(IMC)phase(Ti3Al)and interstitial solid solution composed by elements Ti,N and Al.The hardness test showed that the hardness of the composite coating is markedly increased,which enhanced mainly by TiN.(3)Compared with the substrate,the composite coating erosion resistance showed different resistance character to erosion resistance:The weight loss of the coating increased with the increasing of impact angles,but the weight loss of Ti-6A1-4V alloy decreased with the increasing of impact angles when using the same particle.The weight loss of coating increased with the increasing of the particles' hardness.This is mainly determined by the differences of micro-hardness,wear resistance of the composite coating and Ti-6A1-4V alloy and the characters of the erosion particle.(4)The grains of the coating with ultrasonic vibration became smaller,the thickness of the coating was much thicker than that without applying ultrasonic vibration.The residual stress on surface of the composite coating decreased obviously.The reason was that the dendrites can be interrupted by the ultrasonic vibration during the process of solidification,the broken dendrites were changed into the new nucleation of grains,and then continue to crystallization.Ultrasonic vibration accelerated the flow and heat convection in molten pool.Then the grains were distributed into the molten pool,increasing thickness and hardness of the coating.The residual stress decreased at the same time.