High Temperature Fatigue Deformation Measurement of Ceramics Thermally Sprayed SUS304 Steel Using an ESPI System

Abstract

Surface strains of Al2O3/NiCr thermally sprayed SUS304 steel specimens during the fatigue test (σmax=173MPa, R=0, T=873K) were measured using an electronic speckle pattern interferometry (ESPI) system. The relationships between surface strain and crack initiation/delamination behavior are discussed.The strain values obtained from the ESPI system were confirmed to be almost the same as those from strain gauges on un-sprayed specimens when tensile stresses were loaded at 293K. Thermal expansion deformation and stress deformation at high temperatures were easily measured with the ESPI system. The presence of cracks and delamination on the sprayed coatings can be nondestructively detected by analyzing the strain concentration or decrease. The surface strains of sprayed specimens were almost the same as those of un-sprayed specimens at 873K, indicating that the deformation of the sprayed coatings are always associated with that of the substrate surfaces at high temperature. The maximum surface strain after 1×105 cycles test was a little lower than after 2 cycles test. Surface cracks occurred but stopped at the inner NiCr layer after 2 cycles test at 873K. Many surface cracks and delamination along the interface between the NiCr layer and substrate inte face were confirmed after 1×105 cycles test.