Chapter 5: Raman measurements of stress in films and coatings

Films and coatings have become widely used in structures and components to protect the underlying material from mechanical degradation, corrosion, oxidation and high temperatures or improve surface properties. Residual stress generated in these multi-layer systems is one of the main causes of coating delamination and eventual failure. Systematic measurement and monitoring of the residual stresses are a vital basis for integrity evaluation and remaining life prediction. Raman spectroscopy has been recognised as one of the most important approaches to measure the stress in films and coatings. This review considers the measurement of stresses in films and coatings using Raman spectroscopy. It addresses the following questions: what is Raman spectroscopy, why is stress important for films and coatings, how is strain/stress derived from Raman spectra and what confidence do we have in this technique and the limitations. To elucidate specific issues related to the application of the Raman technique for stress measurement, despite the wide range of coatings available, important films and coating are chosen as representative examples.