Influence Of Laser Remelting On Structure And Performance Of Plasma Sprayed Zirconia Thermal Barrier Coatings

It is an important topic about improving energy efficiency and achieving energy conservation and emission reduction in the sustainable development of contemporary society. Aluminum pistons are widely used in automobile engines, but the low melting point of aluminum alloy limits its combustion chamber temperature. Thermal barrier coating prepared on the surface of aluminum piston can effectively improve the combustion chamber temperature, so as to improve energy utilization ratio. Thus, it’s significant to study thermal barrier coatings prepared on aluminum alloy.In this paper, zirconia (ZrO2-8Y2O3) thermal barrier coatings were prepared on aluminum alloy by plasma spraying technology, and then the sprayed coatings were surface modified using laser remelting technique. The surface and cross section morphology and phase structure of the coatings were studied by means of optical microscope (OM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The influence of laser remelting on thermal insulation performance, corrosion resistance and thermal shock resistance of sprayed coatings were studied systematically.The parameters of ceramic coating were optimized using coating adhesion as evaluation index. The optimum spray current is 800A, and the optimum spray distance is 120mm. In the range of selected parameters, the binding force was firstly increased and then decreased along with the increase of spray current, and the binding force was increased monotonically when the spray distance increased. In order to obtain a well-formed coating, the defocusing distance was selected as 10mm during fiber laser remelting experiment. The laser specific energy should be higher than the critical value of 0.78J/mm2 in order to avoid the surface pits.Plasma sprayed 8YSZ coatings had a layer stacking structure with microcracks and pores whose interior structure were not dense. The sprayed coatings mainly contained the T’ phase and a small amount of M phase. The amount of M phase decreased when the spray distance increase. A dense coating can be achieved and microcracks and pores were eliminated after remelting. Vertical network cracks were observed which penetrated through the whole remelting layer. Horizontal cracks were produced at the interface of ceramic layer while using high specific energy. The M phase was completely eliminated after laser remelting.The heat insulation test indicated that the heat insulation performance of sprayed coatings decreased after laser remelting. The thermal insulation performance decreased with the increase of laser specific energy. Corrosion resistance test results showed that the corrosion resistance of 8YSZ coatings was improved after low specific energy CO2 laser remelting. By contrast, the corrosion resistance decreased after fiber laser remelting. Thermal shock test results showed that the thermal shock lifetime of 8YSZ coating prepared on aluminum substrate was influenced by coating thickness. The higher the coating thickness is, the lower the thermal shock lifetime. Lifetime of the coating was increased slightly after remelting due to the decrease of coating thickness and the release of internal stress.The thermal shock failure of Aluminum based 8YSZ coatings occurred in the interface of bond coat and substrate. Cracks appeared on the edge firstly during the thermal cycle, and it propagated rapidly under the promotion of oxidation process. Such process would cause the coating fall out altogether.