THE EFFECT OF RESIDUAL-STRESS ON MARTENSITIC-TRANSFORMATION IN PLASMA-SPRAYED ZRO2 (8WT-PERCENT-Y2O3) COATINGS

Abstract

The residual stress influences the coating properties in a plasma-sprayed coating layer. This paper presents the effect of residual stresses on the stress induced martensitic transformation in plasma-sprayed partially stabilized zirconia (PSZ) (ZrO2-8 Wt.%Y2O3) coatings. Triaxial stresses were obtained from X-ray dispersive analysis in a PSZ (8 wt.%Y2O3) coated layer. Acoustic signals were also recorded during the indentation test. Acoustic signals from the coating layer were discussed with regard to the residual stresses. The main sources of the signals were martensitic transformation. Acoustic counts decreased with an increase in compressive axial (or radial) residual stress since martensitic transformation was repressed. The critical indentation load for inducing phase transformation varied with the radial (or axial) residual stress. Since the nucleation barrier, DELTAG*, depends on the interaction energy exponentially, the critical stress for martensitic transformation is influenced greatly by the residual stress as the deposition rate decreases.