RELATION BETWEEN THE RESIDUAL-STRESSES AND THE HIGH-TEMPERATURE OXIDATION RESISTANCE OF SUPERALLOYS PROTECTED BY PLASMA-SPRAYED COATINGS .2.

Previous studies on the oxidation behavior of two superalloys, IN100 and CMSX2, protected by LPPS MCrAlYTa coatings, were the basis to relate the high-temperature oxidation resistance to the oxidation stresses. Details are given on the choice of the X-ray diffraction conditions and on the calculations of the crystallographic elastic constants of each phase studied. Dilatometric tests were used to determine the expansion coefficient of the coatings and substrates; a difference in expansion creates stresses during cooling. It has not been possible to determine the Al2O3 oxidation stresses by X-ray diffraction on such systems. Calculations give an Al2O3 stress which agrees with values found by other authors in Al2O3, NiO, or Cr2O3, taking into account the differences in expansion coefficients of the various systems. The as-sprayed coatings are subjected to tensile stresses, due to the Δα between the coating and the substrate. During oxidation, these stresses decrease, owing mainly to the interdiffusion phenomena between the coating and its substrate. This confirms that the more resistant system must consist of CoNiCrAlYTa-coated IN100. © 1990 Plenum Publishing Corporation.