Preparation Of Ti-Al-C MAX Phase Coating By Two-step Laser Method And Its Corrosion And Wear Performance In Marine Environmen

The application of TC4 titanium alloy key components in ocean industrial equipment is gradually shifting from traditional structural components to motion components.However,one of the bottleneck problems that limit its widespread use as a motion component is the poor wear resistance of TC4 titanium alloy.MAX phase materials have become a research hotspot in recent years due to their special phase structure and bonding type,which combine many properties of both metals and ceramics.In this paper,Ti-Al-C composite coatings were prepared on the surface of TC4 titanium alloy using laser cladding technology.Furthermore,the content of MAX phase in the coating was significantly increased by post-laser treatment,in order to improve the corrosion resistance and wear resistance of the TC4 titanium alloy surface and extend its service field.Finally,a two-step process based on laser technology for preparing MAX phase coatings was developed.The specific research contents are outlined as follows:（1）The microstructure and hardness distribution of the laser cladded coating and post-laser treated coating under different post-laser parameters in the laser two-step process were clarified.In the post-laser treated coating,the short rod-shaped and blocky reinforced phase structures dominated by the Ti₂Al C MAX phase are distributed more densely.The microhardness distribution of the coating tends to be uniform,and the most uniform microstructure and hardness distribution can be obtained at a laser power of 1.2 k W and a scanning speed of 1 mm/s.（2）The in-situ synthesis mechanism and phase content transformation of Ti₂Al C MAX phase in composite coatings was investigated in this study.Diffusion of Al atoms leads to the formation of core-shell structure reinforcing phases with Ti C as the core and Ti₂Al C as the shell in laser cladded coatings.During the post-laser treatment process of the cladded coating,the diffusion of C and Al atoms intensifies the intercalation reaction,promoting the formation of two types of MAX phase structures,namely short rod-shaped and blocky MAX phases.The mass fraction of each phase in the cladded and post-laser treated coatings was determined using the Rietveld refinement method.After post-laser treatment under the process parameters of laser power of 1.2 k W and scanning speed of 1 mm/s,the content of Ti₂Al C MAX phase in the coating increased from 9.18 wt.%to 82.93 wt.%.（3）The corrosion and wear behavior of TC4 titanium alloy and composite coatings in artificial seawater were analyzed.By studying the corrosion performance of TC4 substrate,laser cladded coatings,and post-laser treated coatings in artificial seawater,it was found that the post-laser treated coating with a laser power of 1.2 k W and a scanning speed of 1 mm/s showed the best corrosion resistance performance.Its corrosion resistance gradually increased during the soaking experiment of 720 hours.The frictional properties of TC4substrate,laser cladded coatings,and post-laser treated coatings in atmospheric,deionized water,and artificial seawater environments were studied.The wear rate of two types of composite coatings in all three environments was lower than that of the TC4 substrate.The post-laser treated coating had the lowest wear rate in the atmospheric environment,while the laser cladded coating formed a mechanical mixed layer mainly composed of oxides on its wear surface in artificial seawater and deionized water,reducing its wear rate.Ti-Al-C MAX composite coating prepared by laser two-step method can effectively improve the corrosion and wear resistance of TC4 titanium alloy surface.The two-step laser method proposed in this thesis can obtain high content MAX phase coatings,which is a novel strategy to significantly enhance the Ti₂Al C MAX phase content in composite coatings and offers excellent application prospects for the efficient preparation of MAX phase structural components that integrate both structure and function.