Investigation and Comparison of Thermal Shock Behavior of Micro and Nanostructured Thermal Barrier Coatings Applied by Plasma Spray

In this investigation micro and nano-structured ZrO2 coatings were plasma sprayed on Ni based substrates with a MCrAlY coating. Thermal shock was applied on samples by heating in a furnace to 1200 °C and quenching in 25 °C water. SEM and XRD techniques were used for evaluation of microstructure and phase transformations respectively. Resulted life times in thermal cycling test show that number of cycles to failure for nanostructured samples is 38% more than micro structured coatings. Moreover, investigation of samples cross section show that failure of nanostructured samples has occurred near interface of ceramic coating and MCrAlY layer while failure of micro-structured samples can be seen as deep vertical cracks in ceramic layer as well. Evaluation on phases shows no transformation after thermal shock test in any type of samples. Microscopic images show that porosity distribution of micro-structured coatings is more in homogeneous than nanostructured samples. Finite element modeling was used in order to verify experimental results and it shows that thermal stress in nanostructured coatings is 70 MPa less than micro-structured ones.