Residual stress build up in thick thermal spray coatings is a property of concern. The adhesion of these coatings to the substrate is strongly influenced by the residual stress generation during the coating deposition process. In the HVOF spray process, due to lower processing temperature and higher particle velocity as compared to plasma spraying, significant peening stresses are generated during the impact of semi molten particles on the substrate. The combination of these peening stresses together with quenching and cooling stresses that arise after deposition can be of significant importance. In this paper both a numerical finite element analysis (FEA) method, to calculate peening, quenching and cooling residual stresses, and experimental methods, as Modified Layer Removal Method (MLRM) and Neutron Diffraction analysis, are applied. The investigation is performed for thick Inconel 718 coatings on Inconel 718 substrates. Combined, these numerical and experimental techniques yield a deeper understanding of residual stress formation and a tool for process optimisation. The relationship between the stress state and deposit/substrate thickness ratio is given particular interest.

New technologies as Near Net-Shape Spray Forming offer good possibilities to obtain quickly and easily nozzle type refractory components. Excessive material utilisation and laborious machining can be avoided. Cylindrical shape components have been obtained by plasma spraying of yttria partially stabilized zirconia powder on a preshaped mandrel which was subsequently removed. Residual stress analysis through the coatings has been performed using three evaluation methods. A mathematical model able to predict the levels of residual stress is presented and used. A finite element analysis is developed in order to calculate the residual stress field in the near-net shape formed coatings. The validation of the theoretical analysis and mathematical models were performed by neutron diffraction measurements. The experimental results are in good agreement with those obtained by analytical methods and reveal low levels of residual stresses within the sprayed coatings.

The aim of this work is to develop a finite element model that predicts the residual stresses in plasma sprayed parts formed on conical mandrels and removed by various means. The theoretical analyses and mathematical models are confirmed by X-ray diffraction measurements on plasma-sprayed zirconia samples freed from shaped mandrels by means of cooling, melting, and chemical dissolution. Based on test results, the mandrel-cooling removal method produced the highest internal stresses. Paper includes a German-language abstract.