Residual Stress Analysis on Thermally Sprayed Coatings by Means of Optical and Mechanical Methods

The residual stresses present in coatings and layer composites are influenced not only by the thermal and mechanical loads generated during manufacturing, but also by the mechanical and thermophysical properties of the coating and substrate materials. In-process measurement of transient, process-induced stresses may thus enable the manufacturing of coated parts with a residual stress state that lies within a predefined application-oriented stress regime. This paper presents a quasi-nondestructive method by which such measurements may be obtained. A small amount of material is removed from the surface of a part by laser ablation, while optical interference sensors monitor surface deformation caused by stress relaxation and heating due to absorbed laser energy. The new method is evaluated by four-point bend testing using Al5754 plates coated with Al/TiO₂ by atmospheric plasma spraying.