Abstract
The residual stresses of gradation coating components induced by a fabrication process were analyzed by comparison with two-layer composites prepared by a direct bonding.
Firstly, the gradation coating components of stabilized zirconia/nickel based alloy composites were chosen for a finite element method analysis of residual stress distributions. It was verified that the residual stresses at the interface produced by a uniform heating process decreased by use of the gradation techniques. Especially, stress singularities at the edge of the interface of the direct bonding composites disappeared in case of the gradation coating components. However, the residual stresses at the surface of the gradation coating could not be decreased using the gradation techniques.
Secondly, the effects of the gradation geometry and material constants, such as Young's modulus and thermal expansion coefficients on the residual stresses of the gradation coating components were investigated by the thermoelastic analysis using a finite element method. As a result, it was found that the residual stresses could be effectively analyzed by application of the dimensionless parameter, which is σ(1-μ2)/[E2(α1-α2)ΔT](σ; residual stress, μ1=μ2; Poisson's ratio, E2; Young's modulus of coating film 2, (α1-α2); difference of thermal expansion coefficients between substrate 1 and coating film 2, ΔT; temperature difference) in case of the gradation coating components. The analytical results indicated that the dimensionless residual stresses decreased with increasing the coating thickness ratio, t/T (t; coating thickness, T; substrate thickness) and Young's modulus ratio, E2/E1.
