Research On Wear And Corrosion Properties Of HVOF Sprayed WC-Co Coating On TC18 Titanium Alloy

TC18 titanium has been used to aircraft landing gear, because of their excellent properties including high specific strength, low density and so on. These alloys will confront wear and corrosion problems during service in marine and hygrothermal environment. In this article, WC-12 Co and WC-10Co4 Cr coating were fabricated on TC18 titanium alloy using HVOF process. The microstructure, phase composition, micro-hardness, plasticity-toughness, and bonding strength were analyzed. The analysis focused on wear properties and anti-corrosion properties of WC-Co coatings.The results showed that, the thickness of WC-12 Co and WC-10Co4 Cr coating prepared by HVOF parameters was approximate 170?m, without obvious defects. The coatings possess good adhesive strength and low porosity. It is mechanical combination between coating and substrate. WC-12 Co coating mainly contains WC, a little W2 C and brittle ? phase Co6W6 C. The main phase of WC-10Co4 Cr coating is WC, with some W2 C and CoCr phase. The test results of micro-hardness and nano-indentation hardness showed that the hardness and elastic modulus of coatings were significantly higher than TC18 substrate, and WC-10Co4 Cr coating was highest.Friction and wear test under different load and rotate speed at room temperature implied that the friction coefficient, wear volume, the wear scar width and depth of both WC-12 Co coating and WC-10Co4 Cr coating were lower than TC18 substrate, also the wear volume was significantly lower than the substrate. The two coating enhanced the wear-resisting of the substrate, and the WC-10Co4 Cr coating showed the better tribology property. The wear track of WC-12 Co and WC-10Co4 Cr coating appeared smooth and the predominant wear mechanism was abrasive wear. The wear mechanism of TC18 substrate was adhesive and abrasive wear, with mild oxidative wear.The results of electrochemical test, salt spray test and artificial seawater imm ersion test showed that the WC-Co coating could effectively prevent corrosion medium to internal diffusion and protect the TC18 substrate, WC-10Co4 Cr coating exhibited the better corrosion resistance. The major corrosion behavior of WC-12 Co coating was binder phase corrosion, also the WC particles lost the support of the binder phase would fall off. However, pore and inhomogeneity in WC-10Co4 Cr coating were seen as the original of corrosion. In combination with the XRD results, the Cr2O3 passive film was formed on the surface of the coating.