Preparation Of Porous TiO₂ On Titanium Alloy Substrate And Improvement Of Bonding Strength Of The Coating

To improve the bonding feature between the stealth coating and the aerocraft substrate is an important precaution to prolong the service life of the aerocraft which has become one of the research emphases. In this work, the TiO2 porous films were prepared on the TC4 substrate with the aid of anodic oxidation and micro-arc oxidation so as to modify the bonding strength between the substrate and the epoxy coating (with the absorbent Fe).The constant voltage oxidation with the electrolyte of sulphuric acid and the constant current oxidation with the electrolyte of Na2SiO3 were separately adopted in the experiments. Then the as-prepared TiO2 porous film was characterized respectively by means of FESEM and XRD. The effects of technical parameters (such as the voltage, the current, the time, the concentration of the electrolyte) on the morphology, the crystal structure, the thickness and the surface roughness of TiO2 porous film were investigated. It was indicated that the aperture of porous film prepared by anodic oxidation in sulphuric acid distributed from 100nm~200nm. The anatase TiO2 film was obtained at the oxidation voltage of 80V, while the rutile TiO2 was gained at 150V. The porous film prepared by micro-arc oxidation, however, possessed the aperture of 0.1μm~10μm with the thickness of 10μm~50μm, in which the current played a leading role in the transformation of the crystal structure of TiO2 film. Moreover the bonding strength between the substrate and the coating was measured. The results showed that, the bonding strength of the coating prepared by anodic oxidation technique firstly increased and then decreased with the increasing of the voltage, whereas almost constant with varying oxidation time. It reached the maximum value of 9.97 MPa when the voltage and time was 100V and 10min respectively. Differently, for the coating via micro-arc oxidation route, the bonding strength initially increased and subsequently decreased with the increasing current and time, after reaching the maximum value of 33.62 MPa oxidized at 3A for 4min.