Abstract: Theory analysis results show gradient structure can reduce the stress mutation in the joint surface between the coating and the substrate comparing with the nongraded interface, the maximum Mises stress of the coatings is significantly reduced, reasonable graded structure can effectively improve the Mises stress distribution of the coatings and change the characteristics of stress distribution. Optimization of the microstructure is required to achieve reductions in certain critical stress components believed to be important for controlling interface failure, and an adopting gradient structure of 0.25 power exponent is proposed, which can effectively reduce impact loads and Mises stress mutations. Supersonic air plasma spraying is used to produce gradient coatings, coatings with designed exponential graded structure and 6 interlayers are prepared, the coatings specimen are analyzed and tested using for microstructure, bonding strength and impact resistance separately. The XRD analysis results of coatings cross-section show the gradient coating present multilayer structure with designed exponential grade characteristics, impact experimental results show impact resistance properties of coating with 0.25 power exponent graded structure increased by 30% compared with linear gradient structure coating, and increased by 45% compared with 4.00 power exponent graded structure coating. The impact stress of coating with structure of 0.25 power exponent graded reduced, the surfact of coating is not is destroged or peeled off, the graded mutilayer structure is layered, and the impact failure mode of gradient structure of 1.00 and 4.00 power exponent are surface layer peeled off.

Key words: gradient coating;bonding strength;impact load;failure analysis