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 (sin2Ψ) method. A good correlation was found, indicating that Raman microscopy, with its high spatial resolution (2 μm), 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.