Session BB8.2

1:45 PM BB8.2
DETERMINATION OF PROCESS-INDUCED RESIDUAL STRESS IN PLASMA SPRAYED LAYERED AND GRADED COATINGS. O. Kesler, S. Suresh, Dept of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA; S. Sampath, Center for Thermal Spray Research, State University of New York, Stony Brook, NY.

All processing methods used to deposit surface coatings on substrates invariably generate ''intrinsic'' or ''quench'' stresses. These internal stresses, which strongly depend on the specific deposition conditions and processing methods employed, arise from factors such as: rapid quenching of a molten-droplet, non-uniform sintering of the material across the thickness of the coating, non-equilibrium cooling of different phases etc. In addition, temperature excursions cause ''thermal stresses'' to develop due to expansion/contraction mismatch between the constituent phases in the same layer or between layers. An experimental method has been developed which enables the determination of process-induced residual stresses, the elastic modulus and coefficients of thermal expansion of surface coatings of homogeneous or graded compositions. In this method the substrate curvature change is monitored exsitu after before and after deposition. When combined with four-point bend tests, the magnitude of intrinsic stresses through the thickness of the coating can be obtained. In addition, the in-plane Youngís modulus and the coefficient of thermal expansion coefficient can also be determined. Results are presented for plasma sprayed Ni-alumina graded coating and plasma sprayed molybdenum of different thicknesses will be presented.