Abstract
CoNiCrAlY protective coatings are used for insulation from corrosion and oxidation of super alloy substrates in gas turbine blades. The life of a gas turbine blade is significantly affect by the mechanical properties of the protective coating. However, the properties of the coatings themselves have not been clarified, because there are few proper measurement methods for thin coatings. In this study, uniaxial stress-strain responses of atmospheric plasma sprayed (APS) CoNiCrAlY coatings were examined. The coating specimen was tube with the thickness of 0.3 mm. Coating specimens independent of substrates were fabricated by dissolving out the substrates only at the region of gauge area by nitric acid. The stress-strain response was measured using the laser speckle strain measurement method. The coating showed the significant nonlinear stress-strain response. The rigidity increased with an increase of applied compressive stress, and the coating left permanent strain when the compressive stress was relieved. The nonlinearity was decided by the surface roughness which represented the amount of defects in the coating. Nonlinearity of stress-strain response becomes significant if the surface roughness increases. Oxidation ratio was not related with nonlinearity. As compared with low pressure plasma sprayed (LPPS) CoNiCrAlY, the Young's modulus of APS CoNiCrAlY was lower, and total strain was higher. There were not significant differences between the stress-strain response at 873K and that at R.T.
