Locally Resolved Residual Stress Measurements in (Al,Ti)N Coatings Using Raman Spectroscopy

The residual stress state in tool coatings can positively influence tool life. Measurement in strongly curved surfaces e.g. in the cutting edge area is only possible to a limited extent by means of X-ray diffraction (XRD). Raman spectroscopy offers great potential for determining the residual stress state in this area. Therefore, the aim is to determine the fundamental limits of residual stress measurement by XRD on coated carbide tools and to determine and evaluate the suitability of Raman spectroscopy. On typical cutting tools only a small area on the rake face can provide reliable measurement results using conventional XRD methods. Using the XRD results as reference, Raman spectroscopy shows plausible results for residual stresses induced into the coating by mechanical or thermal post-treatment. Coating-induced residual stresses cannot be reliably detected because other coating properties are also changed by modified coating processes that induce higher compressive residual stresses.