Finite element simulation of surface micro-indentation behavior of yttria stabilized zirconia thermal barrier coatings with microstructural characteristic of columnar grains and sub-grains based on a nonlinear contact model

Surface micro-indentation is a very important technique to characterize the mechanical properties and elastic/plastic response behaviour of ceramic coatings. In this paper, surface micro-indentation simulation for yttria stabilized zirconia thermal barrier coatings (TBCs) with microstructural characteristic of columnar grains and sub-grains was performed by finite element method (FEM) based on a nonlinear contact model. The influence of the indenter shape (spherical indenter and flat indenter) on the elastic/plastic response behaviour of the TBCs with microstructural characteristic of columnar grains and sub-grains have been compared and discussed in detail. Especially, the interactions between the columnar grains and the inner sub-grains which are grown on the bond-coat were also considered in the present simulation for the first time. The simulation results indicate that the both the contact friction coefficient (caused between the indenter and the surface of the TBCs) and the inner friction coefficient (caused between the two standing adjacent columnar grains and between the columnar grains and neighbour inner sub-grains) play an important role in affecting the elastic/plastic mechanical response behaviour under the action of micro-indentation. The shear bands and kink bands can be formed due to the action of the micro-indentation. The elastic/plastic deformation mechanism and the failure patterns caused by the micro-indentation were also discussed in detail in this study.