Research On Performance Of Al₂O₃-TiO₂ Coatings By Plasma Spraying And Laser Remelting

A very important problem that the modern industrial society faced is how to further improve the energy efficiency. The research object of this paper is thermal barrier coating which has a broad application prospect in automotive engine. The purpose of this paper was prepare Al2O3-TiO2 coating on aluminum alloy substrate that has good thermal insulation, thermal shock resistance and corrosion resistance, and analyze the influence of different process on the coating performance.In this paper, the Al2O3-TiO2 coatings with different TiO2 content were prepared by plasma spraying technology on aluminum alloy, using OM, SEM and XRD measure the surface and the cross section morphology of coating and phase, thermal insulation, thermal shock resistance and corrosion resistance, choose the appropriate spraying parameter and TiO2 content by optimizing. Because of the defect that is high porosity, the laser remelting was used after plasma spraying. The plasma sprayed coating was remelted with different laser energy density with the selected TiO2 content and the thickness, the improvement of performance of laser remelted coating were researched.Studies show that with the increase of the TiO2 content, thermal insulation is more and more poor, but corrosion resistance and thermal shock performance is more and more high, possible reasons are that the addition of TiO2 is beneficial to inhibit α-Al2O3 to γ-Al2O3. Melting point of TiO2 is lower than Al2O3, in the process of spraying, they dispersed in the brittleness alumina substrate and played a role of hole sealing and release stress by reduce the crack, making the corrosive medium difficult to meet the bonding layer. The coefficient of thermal conductivity of TiO2 is higher than Al2O3 and TiO2 can decrease the coating porosity, so the thermal insulation will decline. The adding of TiO2 can release the interlayer stress between top coat and bond coat and internal stress in the top coat, therefore thermal shock performance was improved.The results showed that with the increase of thickness of AT13 coating, the type of phase has not changed; thermal insulation stays up, the corrosion resistance and thermal shock resistance down after rising first. Possible reason is that the thickness increase, the heat insulation ability enhance. The coating surface crack widen after narrowing first, these crack can become the source of crack that through the coating, porosity was rise after falling first, corrosive medium to the bonding layer change easily after difficult first, so the corrosion resistance fall after rise first. When the thickness is low, because of the high porosity, the antioxidant ability is very poor, therefore thermal shock performance is low. With the increase of the thickness, the interlayer stress and internal stress increase gradually, therefore thermal shock performance decrease.The results of laser remelting showed that with the increase of laser energy density, the surface of AT 13 coatings has serious ups and downs, forming quality decline. After laser remelting, the type of phase did not change, but the peak of each phase changed obviously, so the relative content changed. In certain power range, with the increase of laser power, the thermal insulation and thermal shock resistance decreases. Possible reason is that with laser power increasing, the thickness of the coating and internal porosity decrease at the same time, therefore thermal insulation decrease. When the laser power is small, the main reason of failure is the interlayer stress; when the laser power is large, the main cause of failure is the internal stress. Laser remelting can reduce the interlayer stress between top coat and bond coat, while increase the internal stress.