Papers by Keyword: Substrate Curvature

Abstract: Thin films’ residual stress is often determined by the Stoney formula, using the measurements of the substrate curvature, even if the required hypotheses are not completely respected. In this study, a 2.2 µm titanium nitride coating was deposited by reactive sputtering on a silicon substrate. The Stoney formula was used in order to calculate the residual stress of the film. The radius of curvature was measured, before and after coating by optical profilometer, considering the whole surface of the sample. The effect of the substrate shape (square and rectangular) with various dimensions was investigated. We showed that the shape of the substrate influence strongly the deformation. Moreover, it was highlighted that the choice of the radius (maximum value, minimum value, mean value, with or without initial curvature correction) is critical to the determination of the stress.

Abstract: In this paper, we explored the relationship between thermal aging and the residual stresses developed within a thermal barrier coating (TBC) and the underlying thermally grown oxide (TGO). Superalloy model specimens (CMSX4) with a curved geometry designed to simulate key features of turbine blades coated with air plasma sprayed (APS) 7 wt.% Y₂O₃-stabilised ZrO₂ applied to an Amdry 995 bond coat were oxidised in the temperature range 900°C to 975°C for various lengths of time. Stress measurements on both the TBC and the underlying TGO were made at positions of known curvature using Raman and photo-stimulated piezo-luminescence spectroscopy (PLPS). The residual stress values reflect the interaction between TGO and TBC, which has the potential to be used as an indicator of service lifetime. The results are discussed with respect to the origin of the stress changes and the long term integrity of the coating.