Residual stresses and final deformation of an alumina coating: Modeling and measurement

Mechanical performances of multi-layer coatings are directly affected by thermal history and subsequent residual stress distribution within the sample during thermal spray process. In the present work, a 3D multi-layer model of the plasma spray process was developed to study the thermal and mechanical evolutions of the specimen. The coating build-up was performed by progressive activation of coating layers with a Gaussian distribution profile measured from the corresponding coating. The contribution of sprayed particles to the substrate heating was thus taken into account using a heat flux presenting a Gaussian distribution profile. The decrease of the coating effective properties caused by the presence of porosities and microcracks was investigated by measurement and calculation works. As a result, the temperature evolution, residual stress distribution and final displacement field of the specimen were predicted. At the end of the deposition process, a tensile stress with small magnitude was obtained within the alumina coating. However, the residual stress was turned to a compressive state within the coating after cooling to ambient temperature. A higher cooling rate was found to result in a lower temperature magnitude of the specimen, a lower residual stress within the coating and a lower displacement field of the specimen. The simulated deflection of the specimen was found to agree well with the experimental measurements. (C) 2014 Elsevier B.V. All rights reserved.