Study On The Abrasion Behavior And Corrosion-wear Interaction Mechanism Of TiAl (CN) MAX Phase Composite Coating In Seawater Environmen

The moving parts under load in the marine environment are often subjected to the joint action of corrosion and wear,which aggravates the loss of materials and leads to the failure of parts and brings severe challenges to the reliability of marine engineering equipment.Titanium alloy has the characteristics of low density,high specific strength and strong corrosion resistance in seawater and marine atmosphere,so it is called’marine metal’and widely used in submarines,deep submarines and other marine equipment.However,the poor wear resistance of titanium alloy results in the damage of its surface protective passivation film due to the effect of friction,which makes the fresh surface exposed to the corrosive environment to withstand the synergistic damage of corrosion and wear,limiting the further application of titanium alloy in marine equipment.This paper In this paper,Ti-Al-（C,N）MAX phase composite coating was prepared on TC4 titanium alloy substrate by laser cladding using the mixed powder of Ti4822 titanium alloy and TiC,Al N ceramic binary compound system to improve the corrosion resistance and wear resistance of titanium alloy surface.On the basis of studying the corrosion behavior of TC4 titanium alloy and composite coating in artificial seawater environment,the friction and wear behavior and material loss characteristics under cathodic protection and corrosion conditions were obtained.The main conclusions are as follows:（1）By comparing the effects of different laser melting coating process parameters on the coating quality,it is found that the Ti-Al-（C,N）MAX phase composite coating without unmelted particles,cracks and other defects can be prepared with the laser power of 3000–3300 W and the scanning speed of 120 mm/min.A dense Ti_xAl_y phase short rod-like structure was observed in the matrix of the fused layer with good metallurgical bonding with the substrate.A large number of TiC_1-xN_x phase dendrites and a small amount of equiaxed grains were distributed on the matrix.The microhardness can reach 2.04 times that of TC4.（2）The phase of melted layer changes with the change of powder ratio.TiC and Ti₂Al C in melted layer are gradually replaced by Ti N and Ti₂Al N with the increase of Al N/TiC ratio.The solid solution TiC_1-xN_x changed from solid solution N in TiC to solid solution C in Ti N,from TiC_0.7N_0.3 to TiC_0.3N_0.7,and finally to TiC_0.2N_0.8.MAX phase Ti₂Al C and Ti₂Al N mainly exist at the edge of ceramic phase TiC_1-xN_x when TiC_1-xN_x with high melting point preferentially precipitates from the molten pool.The Al atoms in the Ti-Al melt around the ceramic phase diffuse into the interior gradually and finally form a layer of MAX phase cladding structure at its edge.（3）In the initial immersion stage of artificial seawater,the composite coating and TC4titanium alloy surface passivation film tend to be dense,which can effectively prevent the further corrosion of corrosive medium.With the extension of immersion time,the active cathode ions with strong reducibility in seawater can gradually dissolve the passivation film through the inherent defects on the surface of the material and destroy its stability,resulting in the ability of the passivation film to block the invasion of external corrosive ions and the charge transfer at the interface double layer gradually weakened.The reinforcement in the composite coating precipitates from the molten pool and occupies the grain boundary,which reduces the actual area of corrosion reaction and the reinforcement particles can prolong the path of corrosive ions diffusing into the material,so the corrosion rate of the composite coating is lower than that of TC4 titanium alloy.（4）During the friction process,the friction coefficient of TC4 and TCN2 under corrosion condition can be reduced compared with that under cathodic protection condition due to the lubrication effect of friction chemical products and passivation film.When the load increases to 30 N,The steady-state friction coefficients of TC4 and TCN2 can be reduced to 0.32 and 0.28.The wear mechanism of TC4 in artificial seawater is mainly adhesive wear volume of 3.62×10^-2 mm³,and the wear volume of TCN2 is 3.24×10^-2 mm³caused by abrasive wear and corrosion.（5）The dynamic behavior of passive film removal-formation makes the corrosive medium diffuse into the interior through surface defects of the material.With the increase of applied load from 10 N to 30 N,the self-corrosion potential of TC4 and TCN2 decreases about 0.3 V,The corrosion current increases by about two orders of magnitude,and the pure friction volume loss W_f0 in TC4 decreases from 87.45%to 85.42%,the synergistic effectΔW increases from 12.55%to 14.58%,and W_f0 in TCN increases from 89.89%to 87.83%,andΔW increased from 10.11%to 12.17%.Therefore,the corrosion resistance and wear resistance of TC4 and TCN2 in artificial seawater are mainly determined by their surface wear resistance.