Microstructure And Tribological Property Of Thermal Oxidation Films On Zr-Ti Alloy

The oxidation film was fabricated on the Zr-Ti alloy surface through thermaloxidation in air followed by vacuum diffusion aiming to improve its friction and wearproperty. Then the microstructure and chemical composition of thermal oxide films bythe thermal oxidation in air and the thermal oxidation followed by vacuum diffusionwere analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD),X-ray photoelectron spectrum (XPM) and transmission electron microscopy (TEM).The structure and formation mechanism of thermal oxide films were explored. Theeffect of vacuum diffusion on the composition and microstructure of thermal oxidefilms was also clarified. The hardness and friction and wear properties of thermaloxide films were also measured on a nano-hardness tester and a pin-on-disktribometer respectively, and the effect of thermal oxide film on these properties wasanalyzed as well.The results of the research indicate that thermal oxidation in air leads to an oxidefilm forming on the Zr-Ti alloy surface, of which thickness gradually increases withincreasing oxidation duration temperature and becomes steady when the thicknessreaches a certain value. The formed thermal oxide film will crack or even peel off ifthe temperature exceeds600℃. The oxide film produced by thermal oxidation in airmainly composes of amorphous Ti2ZrO6, of which is crystallized when thetemperature and/or duration of thermal oxidation rise. The vacuum diffusion treatmentleads to formation of a diffusion zone between oxide and substrate, resulting that thethermal oxide film consists of a surface oxide layer and a diffusion zone and the totalthinness of the thermal oxide film is increased. On the other hand, the vacuumdiffusion treatment promotes the crystallization of the amorphous oxide. In contrastwith the case of thermal oxidation in air, the oxygen concentration gradient aroundthermal oxide film decreases after vacuum diffusion due to the existence of diffusionzone. The600℃/20min thermal oxidation followed by500℃/18h diffusion invacuum is selected as a suitable treating condition.Both the thermal oxidation in air and the thermal oxidation followed by vacuumdiffusion dramatically increase the surface hardness of Zr-Ti alloy. Under the samecondition of friction and wear test, the friction coefficient and the wear loss isdistinctly decreased after both the thermal oxidation in air and the thermal oxidation followed by vacuum diffusion, while the adhesion between the friction surfaces isdecreased.