Effects On Phase Structures And Performances Of Oxidated Titanium Alloy(TC4) Through Different Methods

Based on microstructure optimization, three surface oxidation treatments (super-frequency induction heating, micro-arc oxidation and anodic oxidation) were applied for titanium alloy TC4. HITACHI SU-70 Field Emission Scanning Electron Microscopy, Rigaku D/max-rc X-ray diffraction (XRD), CHI600E Electrochemical Workstation and YW-80 salt spray corrosion test chamber etc. were used for determination of phase, microstructure and corrosion resistance. Titanium alloy TC4 were super-frequency induction heated with proper induction distance, effects of induction heating time and shot-blasting of substrate on surface morphology, phase, bonding strength and corrosion resistance were revealed. Using micro-arc oxidation with traces rare earth compound Ce(NO3)2 in electrolyte on titanium alloy TC4, the effects of rare earth element on micro-arc oxidation process and characteristics of coatings were demonstrated. And the effects of voltage on surfaces morphology and phase structure of anodic oxidation is also studied.Heating time plays an important role in the formation of super-frequency induction heating coatings, in which short time results in incomplete coatings and long time makes cracking, non-uniform morphology and low performance. The surfaces morphology, hardness, thickness, phase and element composition of super-frequency induction heated titanium alloys TC4 is best when heating time is 25s-30s, and its critical load during scratch test can reach 32.4N, corrosion resistance is one order of magnitude higher than substrate. Shot-blasted pretreatment also makes a difference to super-frequency induction heated coating. After shot-blasted for 50s and then heated for 25s, Surface morphology of the coating changes obviously with thickness decreasing as well as hardness and bonding strength increasing. Because of compressive surface stress layer produced by shot-blasting, corrosion process is slower and corrosion resistance is one order of magnitude higher than no shot-blasted.The micro-arc oxidation coatings fully covered substrate after 20 min of treatment. When content of rare earth compound Ce(NO3)2 in electrolyte is 0.10g/L, the micro-arc oxidation coatings surfaces’ morphology, phase is good, as well as its corrosion resistance, which is two order of magnitude higher than that with no addition of rare earth element, this indicated that even little rare earth element can afffect micro-arc oxidation process seriously. But when 0.15g/L rare earth compound Ce(NO3)2, rare earth oxide CeO2 appears in the micro-arc oxidation coatings and coatings’ overall performance reduces. The anodic oxidated coatings surfaces’ morphology, hardness, thickness corrosion resistance vary with voltage, and overall performance is better when voltage is 120V.Super-frequency induction heated and shot-blasted specimen expresses best corrosion resistance evaluated by salt spray test, by comparing coatings of three surface oxidation treatments. It can resist 40h of salt spray corrosion atmosphere, meanwhile those of RE micro-arc oxidation coating, anodic oxidation coating and substrate are 31h,25h and 22h, respectively.