梯度结构对氧化铝/镍梯度涂层抗热应力的影响

Influences of Gradient Structure on Thermal Shear Stresses of Al_2O_3/Ni Gradient Coatings

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热载荷作用下有限元模型,利用弹塑性有限元分析方法,分析梯度层的结构形式、厚度及中间层数等参数对涂层热应力分布的影响。模型采用轴对称结构形式,梯度是由系列理想中间层叠加而成,并假定各层结构材料性能存在微小差别,各中间层材料性能描述符合混合准则要求。结果表明:同无梯度结构陶瓷层相比,梯度结构能有效减缓涂层与基体结合面上的剪应力突变,涂层结合部最大剪应力明显降低;合理的梯度结构能改善涂层内部轴向热应力及剪应力分布,改变热应力分布特征,降低陶瓷层与基体结合面上的剪应力,减少塑性变形,从而防止陶瓷涂层在温度变化时过大剪应力作用下脱落。探讨制备层状结构梯度陶瓷涂层时梯度层结构的设计,并提出采用8层中间层、2.0 mm厚线性梯度结构就可有效减缓剪应力的突变的结论。

An elastic-plastic finite element model for gradient coatings with sandwich structure was formulated to study stresses developed at Al2O3 gradient ceramic coatings during thermal stress. The influence of structure parameters such as the layout of interlayer/metal, the thickness of gradient coatings on the thermal barrier resistance was analyzed. Analyses were conducted for a axisymmetric cylindrical specimen geometries relevant to coating. The graded microstructure was treated as a series of perfectly bonded layers, each having slightly different properties. Constitutive relations for the interlayers were estimated using a modified rule-of-mixtures approximation The results show gradient structure can reduce the shear stress mutation in the joint surface between the coating and the substrate compared with the nongraded interface, the maximum shear stresses of the coatings is significantly reduced. Reasonable graded structure can effectively improve the shear stress distribution of the coatings and change the characteristics of shear 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 1.0 power exponent is proposed, and 8 interlayers with 2. 0 mm thick can effectively reduce shear stresses mutations.