Nonlinearity of Uniaxial Compressive Response in Atmospheric Plasma Sprayed Free-Standing CoNiCrAlY Coatings
Hiroyuki WAKI, Izuru NISHIKAWA, Akira KOBAYASHI
Journal of Solid Mechanics and Materials Engineering
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 affected 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) free-standing CoNiCrAlY coatings were examined. The coating specimen was tube with the thickness of 0.3 mm. Coating specimens independent of substrates were fabricated by chemically dissolving out the substrates only at the region of gauge area. The stress-strain response was measured using the laser speckle strain measurement method. The coating showed the significant nonlinear stress-strain response. The stiffness increased with an increase of applied compressive stress, and the coating left permanent strain when the compressive stress was released. The nonlinearity of stress-strain response became significant if the surface roughness increased. The nonlinearity was decided by the surface roughness which represented the amount of defects in the coating. On the contrary, the nonlinearity was not proportional to the fraction of oxidized area. As compared with low pressure plasma sprayed (LPPS) CoNiCrAlY, the Young s modulus of APS CoNiCrAlY was low.
keywords:Mechanical properties; Thermal barrier coating; Plasma spray; CoNiCrAlY; Protective coating; Laser speckle
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