Study On Wear And High Temperature Oxidation Behavior Of TA1 Mechanical Composite Reinforced Layer

TA1 titanium alloy has high specific strength,fatigue resistance,low thermal expansion coefficient,good biocompatibility and other excellent characteristics,but the titanium alloy surface hardness and poor wear resistance,at high temperature is easy to be oxidized to form a non-protective oxide film,limiting its application.In order to solve the problems of TA1,a surface mechanical deformation composite strengthening technology is proposed in this paper.A planetary ball mill is used to obtain a composite gradient layer of nano-structure which is well combined with TA1 matrix at room temperature and N₂ atmosphere,and its tribological behavior and high-temperature oxidation kinetics are studied.Through the single factor test,the mechanical ball milling process with a rotation speed of 350 r/min and a time of 8 h was selected as the final process.The surface mechanical composite strengthening treatment of TA1 alloy was carried out by using WC single reinforcing medium and Ni and WC powder ratios of 1:1,2:1,3:1,4:1 and 5:1,respectively.The microstructure and mechanical properties of the composite reinforced layer were characterized.The results show that a gradient hardening layer composed of WC phase with a thickness of about 40μm is formed on the surface of the alloy treated with a single reinforced medium.The surface hardness of the gradient hardening layer can reach 1100 HV_0.25,and the surface roughness of the strengthened layer is improved.After mixed medium treatment,Ni acts as a binder to enhance the binding between WC and matrix,and a layer of complex phase structure consisting of WC phase and part of Ni_0.3Ti_0.7N phase is formed on the surface of TA1 alloy with a thickness of 40-60μm.The strengthened layer has a gentle gradient structure and is more uniform,and the surface hardness is similar to that of the former.The strengthening mechanism of TA1 alloy and composite reinforced samples was studied.The friction and wear behavior of TA1 alloy before and after mechanical composite strengthening was studied by a self-made reciprocating wear tester under 5 N and 10 N load.The results show that the wear resistance of TA1 alloy is obviously improved after surface mechanical composite strengthening treatment under two kinds of strengthening media.The optimal hardening sample under 5 N load is about 3 times less than the original sample,and the optimal hardening sample under 10 N load is about 6 times less than the original sample.There is a long period of low friction coefficient in the friction process,and the effect of friction reduction is obvious.The wear mechanism of TA1titanium alloy is mainly abrasive wear and adhesive wear,while the wear mechanism of composite reinforced titanium alloy is mainly abrasive wear.At 750℃,800℃and 850℃,the oxidation weight gain of TA1titanium alloy treated with mechanical composite strengthening medium was significantly lower than that of TA1 original alloy.It was found through kinetic model analysis that the high temperature oxidation process of TA1 titanium alloy was mainly controlled by the mixture of surface penetration and diffusion process,and the fitting degree of kinetic curve was high.The high temperature oxidation resistance of TA1 alloy is greatly improved by mechanical composite strengthening treatment.