Critical assessment of high speed nanoindentation mapping technique and data deconvolution on thermal barrier coatings

Abstract

A critical assessment of the high speed nanoindentation technique is performed by testing a complex material system such as thermal barrier coating (TBC). Extensive nanoindentation tests are performed to spatially map the properties of bond coat, top coat and bond coat-top coat interface regions of as-coated and thermally cycled TBCs and the resulting spatial property maps (hardness and elastic modulus maps) are compared with the corresponding microstructures to establish correlations. Excellent correlation is observed between the microstructure and the mechanical properties at the micrometer length scale. The various microstructural features and phases including thermally grown oxide (TGO) at the bond coat-top coat interface are accurately captured by the mapping technique. A deconvolution technique based on k-means data clustering algorithm is used to obtain the phase level properties from the maps and also generate mechanical phase maps to visualize the evolution of mechanical properties with thermal cycling which enables a holistic understanding of degradation mechanisms operating at various levels of thermal cycling. The capabilities of the high speed nanoindentation mapping demonstrated in this work have important implications for microstructure based finite element modeling and also for development of data-driven models for predicting the life of TBCs. Keywords: Thermal barrier coating, Nanoindentation, Mapping, Deconvolution, Thermally grown oxide