Study On Diffusion Mechanism Of Interstitial Elements C,O,N On Titanium Surface

Titanium alloy has the advantages of high melting point,high specific strength,good corrosion resistance?high temperature stability the relatively high chemical activity,and it is easy to react with C,O,N and other gas interstitial elements to form TiC,TiO2,TiN and other compounds.These compounds formed on the surface of Titanium have a relatively high hardness and thus can enhance the hardness and wear resistance of Titanium alloy surface.Based on this,this paper takes TA2 as the research object,through the chemical reaction of titanium with C,O and N gases at high temperature,a permeable layer was formed which contain compounds formed with Titanium and the gas elements,and the microstructure,components of organization evolution and diffusion reaction mechanism of diffusion layer was investigated,the diffusion reaction mechanism was revealed.The characteristic relation between temperature?time and the reaction products?diffusion layer on titanium was also investigated.While subjected to relatively low temperatures between 400? and 700? in a C and O atmosphere,oxidation film was found on the surface of TA2;C atoms in C-O atmosphere were absorbed on the surface of TiO2 to form another amorphous carbon layer due to the high affinity between Ti and C.As the temperature increases,the content of C atoms adsorbed on the surface increased,the amorphous carbon layer can block the diffusion of oxygen into the TA2 matrix to a certain extent.In addition,the adsorption of carbon atoms on the surface increased,the oxygen-inhibiting diffusion ability was enhanced,and the content of oxygen elements on the surface decreased.When the temperature rises above 800?,the diffusion coefficient of C in TA2 increased.As the temperature increases,the C started to continuously diffuse into the TA2 matrix,thus consuming the C element in the surface layer of amorphous carbon,resulted in the thickness reducing looseness of diffusion layer.O atoms in the atmosphere can through the amorphous carbon film easily,coupled with the high temperature to improve the O diffusion coefficient,the content of O element in the surface of TA2 continues to increase.In addition,the study on the surface diffusion layer of TA2 formed at 1100? for 3 h in the atmosphere of C and O showed that TiO2 and amorphous carbon phase were mainly present on the surface of the diffusion layer,while TiC phase was almost absent.Along the depth direction,the amorphous carbon content decreased rapidly,while the content of TiO2 decreased slowly.Meanwhile,the TiC content in diffusion layer increased rapidly,then remained flat,and the content was up to more than 80%.After performing a chemical heat treatment at a temperature of 800??1100? for 5 hours in a nitrogen atmosphere,it was found that with the increase of treatment temperature,the diffusion coefficient of N atom in TA2 matrix increased,and the N atom continuously diffused into the matrix and formed dense nitride with Ti.The nitride formed had a barrier effect on the diffusion of O in the atmosphere to the matrix,thus reducing the O content in thediffusion layer.When the temperature is low(<1000?),the nitride formed by N and Ti is the metastable Ti2N phase.As the temperature continues to rise,N atoms diffuse inward and react with Ti2N to form more stable TiN.After chemical heat treatment at 1100? for different times(1 h,5 h,7 h,10 h,12 h),it was found that with the extension of the holding time,the thickness of diffusion layer of TA2 specimen increased,the content of N element in the diffusion layer increased,and the content of O element decreased.In addition,with the increase of the holding time,the Ti2N phase in thediffusion layer gradually transformed to the TiN phase.