Solidification And Friction Characters Of Al₂O₃Composite Coatings Prepared By Laser Cladding On Titanium Alloy

As one kind of important strategy metal, titanium and its alloy have been widely used in aircraft, ship building, energy and chemical industry. While the alloys also suffer from low hardness, poor tribological behaviors and low resistance to high temperature oxidation, etc, which limit their using in special working conditions. So it’s necessary to provide surface protection of the related components. And alumina ceramics with low density, stable chemical property at high temperatures, excellent tribological properties and other advantages can meet the requirements of the alloys’surface modification. Laser cladding, as a advanced coating preparation technology, have many advantages such as high energy density, rapid melting and solidification, high strength of metallurgical bonding and so on, which make it a effective technology to prepare alumina coatings on the surface of titanium alloy.Based on the significant demand and broad application prospects of the surface modification on titanium alloy, a Nd:YAG CW laser has been used to fabricate Al2O3composite ceramic coatings on titanium alloy in this thesis. And the typical solidification characters and tribological behavior of the coatings have been researched. The specific work presented as follows:(1) According to a set of orthogonal experiments, combined with the elements detection by electron probe, the typical mutual dilution of the alloy and Al2O3-13wt.%TiO2coatings after the cladding process are pointed out. Based on the dilution characters, a set of single-factor experiments are designed to analyze the effect rules of laser power, scanning velocity and powder feeding rate on the dilution condition. And the optimized single track process parameters are given out;(2) During lap coating, the optimized single track process parameters are used to prepare the coatings under different overlapping ratio. Considering the rapid solidification theories of laser processing and the special characters of the ceramic, the microstructures morphology, phase composition, elements segregation and their forming mechanism are studied by optical microscope, electron probe and XRD methods;(3) Observe the effect of different overlapping ratio on the coatings microstructures and tribological behaviors, and discuss the mechanisms. According to the studies above, direct laser cladding of Al2O3-13wt.%TiO2coatings on titanium alloy is realized. And the coatings with high metallurgical bonding strength to the substrate and obvious promotion of tribological property are obtained. The formation mechanisms of the coatings’solidification characters are expounded, in order to provide references to direct laser cladding of alumina coatings on titanium alloy’s surface.