Investigation On Wear Behavior Of Ti-6Al-4V Alloy At Elevated Temperatures

Titanium alloys are widely used in aerospace,automotive and medical equipment and many other fields due to their excellent properties such as high strength,low density and corrosion resistance.Because titanium alloys are difficult to avoid the effects of friction and wear as structural materials,their recognized poor wear resistance limits their applications.At present,a large number of researches on the dry sliding wear behavior of titanium alloys have focused on the formation and function of tribo-oxide layers,and little researches have been done on the material’s own response.Therefore,this paper will explore the high temperature wear behavior of titanium alloys from two perspectives,combining the role of tribo-oxide layers on the friction-affected surface of the material in terms of microstructural evolution and mechanical properties.In this paper,the dry sliding wear test of Ti-6Al-4V alloy from room temperature to high temperature was carried out by using a wear machine.The sliding speed was1.0 m/s and 0.5 m/s respectively,the temperature range was 20～400℃,and the load range was 10～240N.The wear rate variation curve with load under different speeds and temperatures was drawn.SEM,EDS,XRD,EBSD and other means were used to comprehensively observe and measure the wear surface and cross-section morphology,element composition and content,compound type,microstructure and hardness change,recrystallization degree,etc.,and analyzed different experiments.The wear mechanisms of the alloy under different test conditions were analyzed and summarized,and the transition diagram of the wear mechanism was drawn.The results showed that the wear process of Ti-6Al-4V alloy can be divided into two stages:slight wear and severe wear.At a sliding speed of 1.0 m/s,the main wear mechanisms in the mild wear stage include oxidation wear,delamination wear,oxide layer peeling and slight plastic deformation+adhesive wear,and the main wear mechanism in the severe wear stage are severe plastic deformation+adhesive wear.At a sliding speed of 0.5 m/s,the main wear mechanisms in the mild wear stage are oxidation wear+abrasive wear,mechanical mixed layer spalling and slight plastic deformation,and the main wear mechanisms in the severe wear stage are mechanical mixed layer damage and severe plastic deformation.The study found that at a sliding speed of 1 m/s,the thermal softening of the wear subsurface structure due to the dynamic recrystallization transformation reduces the wear resistance of the alloy,which was the main factor leading to the slight to severe wear transition of Ti-6Al-4V alloy.The critical dynamic recrystallization temperature criterion can be used to evaluate the transformation load,namely,T_S≥T_DRX.However,when the temperature increased to 400℃,the wear rate suddenly decreased to a very low level,and the transition from mild to severe wear was delayed,so the temperature criterion was no longer applicable.While at a sliding speed of 0.5m/s,the failure of the mechanically mixed layer controls the mild-to-severe wear transition of the alloy when the test temperature were 20℃and 50℃.However,the critical dynamic recrystallization temperature criterion can still determine the dynamic recrystallization transformation of subsurface materials accompanied by severe plastic deformation wear mechanism.And the mild-to-severe wear transition at100-250℃still applies to this criterion.