Research On Vacuum Thermal Oxidation Process Of Ti6Al4V Titanium Alloy Surface And Its Effect On PVD Treatment

Titanium and titanium alloys have low hardness and poor friction and wear properties,which limit their use under wear-resistant conditions.Surface treatment technology can effectively improve the hardness and wear resistance of titanium alloys.Among them,vacuum thermal oxidation can form a certain thickness of oxygen diffusion layer on the surface of the alloy through oxidation and vacuum diffusion means,thereby improving the surface properties of the titanium alloy.However,vacuum thermal oxidation only improves the surface hardness and corrosion resistance of titanium alloys,and its friction and wear performance is not greatly improved.The use of PVD technology to prepare TiN film coating on the surface of the material can increase the hardness of the material,enhance the corrosion and wear resistance,and reduce the surface roughness of the material.However,the hardness of Ti6Al4V alloy is low.After TiN is directly prepared on the surface of titanium alloy,the substrate is easily deformed and the surface film is broken and peeled off under an external load.The bonding performance may not be ideal,and the coating cannot strengthen the substrate.If the TiN film is prepared on the surface of the titanium alloy treated by vacuum thermal oxidation,the surface layer of the material is strengthened by the vacuum thermal oxidation,and the strengthened layer acts as a transition layer.The hardness is improved,and it is not easy to deform.It can provide support for the TiN film coating on the surface and improve the coating performance.Performance and working life,thereby improving the surface properties of Ti6Al4V alloy.This thesis first uses vacuum thermal oxidation technology to oxidize and diffuse Ti6Al4V titanium alloy,and investigates the effect of vacuum thermal oxidation treatment on the microstructure and properties of titanium alloy at different temperatures and times,and then performs oxidation treatment and vacuum diffusion treatment on untreated Ti6Al4V TiN films were prepared on the surface of the titanium alloy samples using PVD multi-arc ion plating technology to obtain composite treated titanium alloy samples,and the film-base bonding force and performance of the composite treated samples were studied.The main findings are as follows:(1)In the oxidation stage,the rutile TiO₂ oxide layer and oxygen diffusion layer formed on the surface of the titanium alloy improve the hardness,corrosion resistance and wear resistance of the titanium alloy.As the oxidation temperature increases,the thickness of the oxide layer and oxygen diffusion layer on the surface gradually increase,and the surface of the oxide layer gradually becomes rough.After oxidation treatment at 800°C,the oxide layer generated on the surface can cover the entire sample surface.Smooth,the sample has the best corrosion resistance.After oxidation treatment at 850°C,the hardness of the titanium alloy is the highest,but the oxide layer is rough and porous,and the corrosion resistance is reduced.(2)In the vacuum diffusion stage,due to the increase of heat treatment time and the diffusion of O atoms,the equiaxed?grains in the titanium alloy increase,the grains grow,and the?grains in the diffusion layer gradually shrink and transform into?grains.With the increase of diffusion temperature and time,the rutile TiO₂oxide layer generated in the oxidation stage accelerates to dissolve,and the thickness of the diffusion layer increases.When the diffusion temperature is low,anatase TiO₂and Ti₂O are formed on the surface.As the temperature rises,the surface oxides gradually decrease.After being diffused at 850°C for 20 hours,after polishing treatment,there is basically no rutile TiO₂ and oxides on the surface of the titanium alloy,and the diffusion thickness can reach 183?m.After testing,the corrosion resistance and wear resistance after diffusion treatment are better than the samples after oxidation treatment.The wear rate of the samples after diffusion treatment is0.541 times that of the untreated Ti6Al4V samples,and the wear mechanism is transformed into abrasive wear.Vacuum thermal oxidation treatment improves the hardness,corrosion resistance and abrasion resistance of titanium alloys.(3)Using PVD multi-arc ion plating to prepare TiN film on the surface of Ti6Al4V,oxidation treatment and diffusion treatment of titanium alloy samples.After testing,Ti6Al4V has low hardness and poor film-base bonding performance of 7.2N.Due to the presence of oxides on the surface of the oxidized sample,the film will fall off on the surface of the sample after PVD treatment.The surface film will be broken and peeled at the beginning of the scratch test.The base bonding performance is poor.After diffusion treatment,the oxide content on the surface of the sample decreases,and the film-base bonding performance increases.The sample surface after 850°C diffusion treatment for 20 hours is basically free of oxides.The film-base bonding force can reach 31.2N,the corrosion potential increases by 0.495V,and the corrosion current density A drop of two orders of magnitude,the hardness is 1320HV,and the overall performance is the best.Studies have shown that the hardness of the sample and the oxides formed on the surface will affect the film-base bonding performance and the thickness of the surface film of the sample after PVD treatment,thereby affecting the mechanical properties and corrosion resistance of the sample after coating.After the composite treatment,the wear mechanism of the titanium alloy is mainly abrasive wear,supplemented by adhesive wear.The wear amount is 4.583×10^-7g(N·m),and the wear resistance is improved.The oxygen diffusion layer with stepped hardness generated on the surface after vacuum thermal oxidation treatment,as a sub-surface layer,improves the surface hardness and corrosion resistance of the titanium alloy,and exhibits good bonding force with the TiN film prepared by PVD,which improves the coating.Layer performance and life.The combined treatment of vacuum thermal oxidation and PVD can significantly improve the hardness,corrosion resistance and wear resistance of titanium alloys.