X-ray residual stress measurement in metallic and ceramic plasma sprayed coatings

Processing-induced residual stresses play an important role in the producti on and performance of thermally sprayed coatings, Their precise determinati on is a key to influence the coating properties by modification of process variables and to understand the processing-structure-property relationship. Among various methods for residual stress measurement, x-ray diffraction h olds a specific position as being nondestructive, phase distinctive, locali zed, and applicable for real parts, The sin(2) psi method is commonly appli ed for bulk materials as well as coatings. However, the results are often r eported without sufficient experimental details and the method is used in i ts simplified form without justification of certain assumptions. In this investigation, the sin(2) psi x-ray diffraction method was used to measure residual macrostress in plasma sprayed metallic (nickel, NiCrAlY, a nd molybdenum) and ceramic (ZrO2 + 8% Y2O3) coatings. Reproducibility of th e method was tested and the assumptions allowing its use are discussed and experimentally verified. For nickel coatings, a comparison with hole drilli ng and neutron diffraction measurements is presented. The influence of proc essing factors such as deposition temperature and coating thickness is stud ied and the results are discussed.