Titanium alloys are used in the aerospace industries,chemical industries,biomedicine,marine ships and other fields because of their high strength-to-weight ratio,good corrosion resistance,and biocompatibility.However,titanium alloys have low hardness and poor wear resistance,which limit their applications,especially under sliding contact.Plasma nitriding(PN)is an effective method for im-proving titanium alloy's tribological properties.PN can produce a composite layer composed of TiN and Ti2N to improve the friction and wear properties of titanium alloy.However,the high temperature in the ni-triding treatment results in a brittle"α-stabilized layer"(a continuous layer of α phase titanium enriched with interstitial nitrogen atoms)and unfavorable phase transformations in the substrate that can impair the fracture toughness,ductility,and fatigue properties.In this study,a low-temperature plasma-composite treatment,consisting of plasma oxidizing and oxynitriding,has been developed to improve the hardness and wear resistance of Ti-6Al-4V alloy.The effect of the preoxidation process on the surface microstruc-ture,phase composition,and wear performance of titanium alloy was studied.The microstructure and phase composition of the plasma-composite layer were observed using SEM,TEM,XRD,and other methods.The results showed that the composite layer of titanium alloy treated using plasma-composite-treatment is composed of compound and diffusion layers,and the phase is TiO2(rutile)and TiN0.26.Micro-hardness and wear-resistance properties of the composite layer were characterized using microhardness tester,nanoindentation,and reciprocating-friction tester.The plasma-composite treatment can increase in-filtration depth of the diffusion layer,surface hardness,elastic modulus,and wear resistance of the titani-um alloy more than the traditional nitriding process.
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