Abstract
This study numerically investigates cyclic thermal shock behavior of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a nonlinear mean-field micromechanical approach, which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface. The fabrication processes for the FG TBCs have been also considered in the simulation. The effect of creep and compositional gradation patterns on micro-stress states in the FG TBCs during thermal cycling has been examined in terms of the amplitudes, ratios, maximum and mean values of thermal stresses. The compositional gradation patterns highly affect thermal stress states in case of high creep rates of ZrO2. In comparison with experimental data, maximum thermal stresses, amplitudes and ratios of thermal stresses can be effective parameters for design of such FG TBCs subject to cyclic thermal shock loadings.
Highlights
Ceramic-metal functionally graded thermal barrier coatings (FG TBCs) have been attracting a great deal of attention for structures working under super high temperatures and temperature gradients
Macroscopic heterogeneity means the gradation of microstructures and material properties through the thicknesses of the FG TBCs, and microscopic heterogeneity is due to the fact that the composite materials are composed of several constituents, usually metals and ceramics
The purpose of the current study is to numerically investigate thermal cyclic behavior of ZrO2/Ti functionally graded thermal barrier coatings (FG TBCs) based on a nonlinear mean-field micromechanical approach [5], which takes into account the time-independent and dependent inelastic deformation, such as plasticity of metals, creep of metals and ceramics, and diffusional mass flow at the ceramic/metal interface
Summary
Ceramic-metal functionally graded thermal barrier coatings (FG TBCs) have been attracting a great deal of attention for structures working under super high temperatures and temperature gradients. FG TBCs are advanced multiphase composites that are engineered to have a smooth spatial variation of material constituents. This variation results in an inhomogeneous structure with smoothly varying thermal and mechanical properties. The advantages of FG TBCs as an alternative to two dissimilar materials (ceramics and metal) joined directly together include smoothing of thermal stress distributions across the layers, minimization or elimination of stress concentrations and singularities at the interface corners and increase in bonding strength [3]. Macroscopic heterogeneity means the gradation of microstructures and material properties through the thicknesses of the FG TBCs, and microscopic heterogeneity is due to the fact that the composite materials are composed of several constituents, usually metals and ceramics. In order to make the best use of such heterogeneous materials, the formulation of the constitutive relation from the standpoints of these two different scales is required [4,5]
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