Study On The Structure And Performance Of The Cu-Al₂O₃ Gradient Ceramic Coatings Prepared By Plasma Spraying

Spraying ceramic coatings on metal substrate by thermal spraying technology has been widely utilized in many fields. However, because of the differences of physical properties between the ceramics and metals, high residual thermal stress will be introduced during the course of preparing and applying, and these induce the coatings have poor adhesion stress, low thermal-shock resistance and high porosity, thus limit the applied range of ceramic coatings. According to the fundamentals of that metal-ceramic coatings can release stress concentration, improve the adhesion strength of coatings, Cu-Al₂O₃ gradient coatings were fabricated by plasma spraying in this paper. The distribution and microstructure of the gradient coatings were analyzed by SEM and metallomicroscopy. The adhesion strength, thermal-shock resistance, porosity, hardness and wear-resisting property of coatings have also been tested, and the characteristics of physical properties of Cu-Al₂O₃ gradient coatings were studied primarily. Moreover, the distribution states of thermal stress of coatings were analyzed by Ansys software. It offers the theory support for the design and preparation of coatings in the future.By analysis and study, the results indicate:The Cu-Al₂O₃ gradient coatings have typical layer structure and mechanical bond with the substrate mainly. From the substrate to the surface of coatings and along the direction of thickness, the content of Al₂O₃ is increased and the content of Cu is decreased, and without distinct componential saltation and macroscopic interface among the different compositions, the gradient coatings show the characteristic that structure is not uniform macroscopically but consecutive microscopically.Compared to double-layer coatings, the gradient coatings have higher adhesion strength and thermal-shock resistance, which are twice and four times of those of douber-layer coatings. The porosity of gradient coatings are decreaseing as the Al₂O₃ content increasing, and the surface ceramic layer has the highest porosity which is 8.74%. Following increasing of Al₂O₃ hard phase, the hardness of coatings is increased, and the pure ceramic layer has the highest one. The hardness, microstructure, pore, and the adhesion strength among the particlesof coatings have influence on the abradability of coatings. The secondary outer layer(the content of Al₂O₃ is 80%, the content of Cu is 20%) has the best abradability, When the are lesser, the major wear mode of coatings are cutting and ploughing, and when the have many Al₂O₃ hard phase, the main wear mode of coatings translate into the hard phase breaking and pull-out.Both the double-layer coatings and the gradient coatings have large residual stress in the fringe of coatings interface. The utility of transition layer recessive relaxed the stress mutation. Thus the gradient coatings have better adhesion strength and thermal shock resistance in comparison with double-layer coatings.