Raman microscopic studies of residual and applied stress in PVD hard ceramic coatings and correlation with X-ray diffraction (XRD) measurements

In order to assess the complementarity of Raman microscopy and X-ray diffraction for the measurement of residual stresses in PVD hard coatings, a series of TIAlN/VN superlattice coatings were deposited onto high speed and stainless steel substrates. Raman spectral shifts of the main optical phonon mode at ca. 650 cm(-1) from lattice vibrations of the TiAlN/VN polycrystalline coatings (which are sensitive to residual stress) were correlated with stress values obtained using X-ray diffraction by the glancing angle (sin(2)Psi) method. A good correlation was found, indicating that Raman microscopy, with its high spatial resolution (2 mum), short sampling times (1-10 min) and non-destructive nature, provides a viable alternative method for determination of residual stresses. A calibration method, using a four point bending rig, has also been developed to strain the TiAlN coatings and assess the material response to externally applied stress using the Raman technique. (C) 2003 Elsevier B.V. All rights reserved.