Using ESPI system to measure high temperature fatigue deformation of ceramics thermally sprayed SUS304 steel

Abstract

The strains in an Al₂O₃/NiCr coating, which was thermally sprayed on SUS304 steel, were analyzed using an electronic speckle pattern interferometry (ESPI) system during fatigue testing (R = 0, σ_max = 173 MPa) at high temperature of 873 K. The strain changes with the crack initiation in the coatings and the delamination at the coating/substrate interface are accordingly discussed.

Surface cracks originated from the top coating of Al₂O₃ and stopped at the bond coating of NiCr after 2 cycles test at 873 K. Many surface cracks and delamination along the NiCr/substrate interface were confirmed after 1 × 10⁵ cycles test. The strain values of un-sprayed specimens obtained from the ESPI system agreed with those measured by the strain gauge when tensile stresses were applied at room temperature. The deformation by thermal expansion and stress application at high temperatures can also be easily measured using this method. The strain on sprayed specimens was almost the same with that on un-sprayed specimens at 873 K, indicating the deformation in the coatings are always associated with that of the substrate surfaces at high temperature. By comparing and analyzing the strain distribution on the coating surface, the presence of cracks in the coatings and delamination at the coating/substrate interface can be in-situ and nondestructively detected.