Tribo-corrosion Mechanism Of Coatings With High-wearing Resistance Prepared On TC17 Titanium Alloy

The low surface hardness,poor thermal conductivity,high friction coefficient and adhesive wear of titanium alloys have hindered their applications in many industries.Therefore,surface engineering technology has become one of the research hotspots to improve the surface hardness,wear resistance and corrosion resistance of titanium alloys.In this paper,a micro-arc oxidation(MAO)coating with metallurgical bonding with the substrate was firstly grown in situ on the surface of TC17 titanium alloy by MAO.Then,high-power pulsed magnetron sputtering technology was used to deposit single-layer TiN layer and multi-layer TiN/Ti soft-hard alternating layer on the surface of MAO coating to fabricate TiN-MAO composite coating and TiN/Ti-MAO soft-hard alternating caoting with high wear resistant,in order to further improve the hardness and density of MAO coating,as well as its wear and corrosion resistance in harsh service environment.The microstructure,composition and corrosion wear behavior of TC17 titanium alloy substrate and its surface coatings in simulated solution were studied.The main results obtained are as follows:The friction coefficient and wear rate of TC17 titanium alloy substrate are significantly improved due to its corrosion.The substrate of TC17 titanium alloy is eroded by H+ and Cl-ions in acidic solution,resulting in the corrosion of Al-rich a phase in the substrate,which on the one hand increases the surface roughness of the substrate as well as the friction coefficient.On the other hand,the shear strength of the substrate surface material is reduced,resulting in serious adhesive wear on the wear mark surface,leading to a significant increase in the wear rate.However,with the increase of solution concentration,a large number of ions are adsorbed on the wear mark surface to play a good lubrication effect,which effectively alleviates the wear process of the substrate.The MAO coating prepared on TC17 titanium alloy can effectively reduce the friction coefficient and wear rate of the substrate,but the wear rate increases obviously with the pH value decrease of the solution.In the process of tribo-corrossion,the micropores on the surface of MAO coating can effectively store the hard wear debris generated in the grinding process of friction pair,so as to improve the density and strength of MAO coating surface and slow down the wear process of MAO coating.However,the H+and Cl-ions in the solution can quickly penetrate into the interface between MAO coating and substrate through structural defects such as micropores and microcracks in the MAO coating and then cause corrosion,resulting in the reduction of its bonding strength,which promotes the premature corrosion cracking and wear off of MAO coating.Based on the porous micro-nano structure on the surface of MAO coating,a hard TiN layer is deposited on its surface to further improve its surface hardness and density,and effectively inhibit the brittle cracking and wear off of MAO coating.The TiN layer completely covers the surface of MAO coating and has a meshing structure with it,which not only effectively hinders the penetration of H+and Cl-ions into the composite coating,but also significantly improves the bonding strength between the TiN layer and MAO coating.During the process of tribo-corrosion,brittle cracking occurs locally in the outer TiN layer,and the hard wear debris is embedded in the MAO coating,which not only improves the density and strength of the wear scar surface,but also plays an excellent wear-resistant and antifriction effect through the rolling effect of hard particles on the wear scar.HiPIMS technology was applied to deposit hard TiN layer and pure Ti layer alternately on the surface of MAO coating,which can effectively inhibit the initiation and propagation of microcracks in the coating,so as to significantly improve the wear resistance of MAO coating.On the one hand,the pure Ti layer in the TiN/Ti-MAO soft-hard alternating coating can react with solution penetrated from the TiN layer to form a dense oxide film,which further hinders the penetration of corrosive ions into the MAO coating.On the other hand,the pure Ti layer has good toughness,which can effectively alleviate the impact of grinding ball on the coating and restrainc the occurrence of local brittle cracking and wear spalling of TiN layer.