Evaluation of Fracture Mechanics in Ceramics Splay-Coated Materials by Using Fast 3-D Digital Image Correlation Method

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Low pressure plasma spraying (LPPS) is used to prepare CoNiCrAlY alloy coatings for insulation from the high temperature corrosion and oxidation. However, mechanical properties of LPPS CoNiCrAlY coatings, which have important effects on the life of a gas turbine blade, have not been clarified. In this study, monotonic and cyclic deformation behaviors of the CoNiCrAlY coatings under uniaxial compressive loading were examined. Coating specimens independent of substrates were fabricated by dissolving out the substrates only at the region of gauge area by nitric acid. The thickness of the coatings were 300μm. The stress-strain response was measured using the laser speckle strain / displacement gauge (SSDG). The coating showed the nonlinear stress-strain response with a considerably low elastic modules. It was found that the coating left permanent strain by compressive loading: the coating was hardened by compressive loading. The generated strain was also found to decrease furthermore by undergoing cyclic compressive load. The coatings with high porosity showed that the large strain, large permanent strain and low Young's modulus.