New Process Design Of High Temperature Oxidation Resistant Film On TC4 Based On Microarc Oxidation

In this paper,use pulsed DC power source-MAO method,processed in the silicate-phosphate system for TC4 titanium alloy which is the most amount of aviation industry,the main purpose is to improve the high temperature oxidation resistance and corrosion resistance of TC4 alloy.The effects of electrolyte composition,concentration and electrical parameters?including voltage,current density,duty cycle,pulse frequency?and oxidation time on the microstructure and surface quality of MAO film surface?including surface roughness,film thickness,binding force?were investigated by orthogonal optimization method.The microcosmic properties of the coatings were evaluated by means of SEM,XRD and EDS,and the effects of high temperature oxidation resistance,corrosion resistance,abrasion resistance and resistance Micro-hardness assessment,the final screening of a set of optimized micro-arc oxidation process,and concluded as follows:When other parameters are invariable,along with the increased of oxidation time or oxidation voltage or current density,the surface finish,film thickness,bonding strength,micro-pore size of micro-arc oxidation coating layer were increased,the hole density was decreased,the relative content of rutile TiO₂ in the film was increased,the relative content of anatase TiO₂ was first increased and then decreased,and the corrosion resistance of the film was first increased and then decreased;accompany with the duty atio rised,the surface finish and the film thickness were rised,adhesive force and resistance to corrosion were dropped follow the duty ratio rised;companion with the pulse frequency rised,the surface finish,micro-pore diameter and film dimension of the MAO film layer were reduced,the adhesive force was rised and the resistance to corrosion was reduced,and the diffraction intensity of the rutile TiO₂ was rised first and then downed,the diffraction intensity of anatase TiO₂ was first weakened and then enhanced.The TC4 titanium alloy has no resistance to high temperature environment above700 degree,but the oxidation resistance of TC4 titanium alloy with MAO is more than 4times than base metal in the range of 700 degree to 900 degree.The TC4 titanium alloy in concentrated sulfuric acid was quickly failed,but the TC4 titanium alloy which was treated by MAO in concentrated sulfuric acid was corrosioned for 60h and then still has a good performance,the corrosion resistance was increased by more than 13 times higher than the base metal.At the same time,the surface hardness of the TC4 titanium alloy which was treated with MAO is more than 2 times higher than the base metal,and the anti-friction was greatly rised ibid.The microcosmic hardness and anti-friction of the sample can still be maintained at high temperature.Based on the above analysis of a series of factors and performance analysis,a set of MAO process with the best high temperature oxidation resistance and corrosion resistance was obtained:Electrolyte formulation:Na₃SiO₃ 15g/L,Na₃PO₄ 10g/L,NaOH1g/L and Na₂WO₄ 2.5g/L;Electrolyte concentration:0.04 mol/L;pulse frequency is500Hz,current density keep at 16A/dm²,voltage set at 475V,duty cycle is 10%;oxidize for 75 min.