STRAIN GRADIENTS IN PLASMA-SPRAYED ZIRCONIA THERMAL BARRIER COATINGS

Neutron diffraction was used to measure the residual strain field in p lasma-sprayed zirconia thermal barrier coatings (TBCs). Data were coll ected at the British neutron spallation source of ISIS (Didcot), on EN GIN, a recently installed TOF (time-of-flight) instrument designed for residual strain depth profiling. Its particular geometry permitted a direct measurement of the interplanar distances of crystallographic pl anes lying parallel to the component surface as well as the measuremen t of zero-strain reference samples. The latter were annealed samples o f the three present phases: zirconia (top coat), NiCoCrAlY (bondcoat), and copper (substrate). In this way epsilon(33), the strain component perpendicular to the sample surface, was determined at several positi ons inside the component, for all the present phases. The results of t his analysis, consisting of a strain profile throughout the entire cro ss-section of the coated component, were integrated by those obtained by a destructive testing, performed after TOF data collection, consist ing in the measurement of curvature change of the ceramic after substr ate removal by chemical attack. (C) 1998 Elsevier Science S.A. All rig hts reserved.