梯度结构对氧化铝陶瓷涂层抗冲击载荷性能的影响

梯度结构陶瓷涂层以其优异的抗热震性表现出巨大的工程应用前景。为推动梯度陶瓷涂层在机械零件表面强化上的应用，采用“三明治”式梯度结构形式，建立镍基氧化铝梯度陶瓷涂层在冲击载荷作用下有限元模型，分析冲击载荷作用下涂层的力学性能，以及梯度层的结构形式、厚度及层数等参数对涂层的力学性能影响。结果表明：较无梯度结构陶瓷涂层相比，梯度结构能有效减缓涂层与基体结合面上的应力突变，涂层内部最大Mises应力明显降低，合理的梯度结构能改善涂层内部Mises应力分布，改变应力分布特征，减缓表面陶瓷涂层的冲击应力，从而防止陶瓷涂层在冲击载荷作用下脱落。最后对制备层状结构梯度陶瓷涂层时，如何进行梯度层结构设计进行了探讨，并提出了采用0.25次方幂指数梯度结构，得出10层中间层就可有效减缓冲击载何、降低Mises应力突变的结论。

Influences of Gradient Structure on the Impact Resistance of Al2O3 Ceramic Coatings

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.