Abstract: An elastic-plastic finite element method numerical model for gradient coatings with sandwich structure is formulated to study stresses developed at Al2O3 gradient ceramic coatings during impact loads. The influence of structure parameters such as the layout of interlayer/metal, the thickness of gradient coatings on the impact resistance is analyzed. The results are compared with those obtained from the nongraded interface to assess the potential for achieving impact stress reductions. Analyses are conducted for a axisymmetric cylindrical specimen geometries relevant to coating. The graded microstructure is treated as a series of perfectly bonded layers, each having slightly different properties. Constitutive relations for the interlayers are estimated using a modified rule-of-mixtures approximation, and strain and stress distributions are calculated for simulated falling rigid ball. The 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. And the results also show reasonable graded structure can effectively improve the Mises stress distribution of the coatings and change the characteristics of stress distribution. It shows that in some cases, 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, and 10 interlayers can effectively reduce impact loads and Mises stress mutations.

Key words: Gradient coating, Impact load, Mechanical properties analysis, Structure design