Assessing thermal residual stress reduction from composition grading at material interfaces: A numerical modeling study

Elastic-plastic finite element models are utilized to study residual stress and strain development at graded ceramic-metal interfaces during cooling from an assumed fabrication temperature to ambient conditions. Results are compared with those obtained for sharp (non-graded) interfaces to assess the potential for achieving residual stress and strain reductions. The graded material region is modeled as a series of perfectly bonded layers, each having slightly different mechanical and thermal properties. Constitutive relations for the composite interlayers are approximated using a modified rule-of-mixtures approximation. Ni-Al₂O₃ was used as a model system, and calculations are performed for two axisymmetric geometries. Significant geometrical effects on peak stresses are observed in the graded materials. The results illustrate the importance of accounting for plasticity when comparing graded and non-graded interfaces. For one specimen geometry, both linear and a variety of nonlinear composition gradients are considered, demonstrating the necessity of microstructure optimization for reduction of certain critical stress components.