PROGRESS IN X-RAY DIFFRACTION OF RESIDUAL MACRO-STRESS DETERMINATION RELATED TO SURFACE LAYER GRADIENTS AND ANISOTROPY, S.J. Skrzypek, A. Baczmanski, pp. 134-145

The well known sin2p method for macro-stress measurement elaborated for BraggBrentano geometry has some disadvantage e.g. penetration depth of X-ray beam varies during m.easurement. This is particularly important in the case of coatings or surface layers where residual stresses appear with large gradients, The new version of the sin’v method, named gsin’w (based on the grazing angle scattering geometry) was applied for determination of the macro-residual stresses in TiN coatings deposited on sintered WC and on sintered high speed steel. These types of samples present a wide range of residual stresses i.e. from large tensile to large compressive. Using the g-sin2w method the stresses are determined for chosen near surface layers for which effective penetration depth remains almost constant during measurement. Anisotropic elastic constants were used for calculations. The measured results were compared with a model based on thermal shrinkage. Introduction The most universal sir& diffraction method enables measurement of the macro-stress tensors and the elastic properties of polycrystalline materials. If a known stress can be applied during measurement, diffraction elastic constants (DEC) and elastic constants or mechanical compliances can be measured [l-4 J. The diffraction methods have several important features such as a non-destructive and non-reference character, possibility of stress analysis for multiphase and anisotropic materials. The conventional well-known sin’ p method has some disadvantage i.e. penetration depth of Xray rad.iation varies during experiment when the w angle is changing. This is particularly important for thin coatings, films or surface layers where the residual stresses have large gradients which can reach several hundreds MPa/p.m. Till now the gradients of residual macrostresses in surface layers were measured using different wavelengths [5,6] or by gradual removing of surface layers and following measurements [7]. In this work the g-sin’ly method based on the grazing incidence angle X-ray diffraction (MD) geometry is applied to macro-residual stresses (RS) measurement in TiN coating. Van Acker et al. [8] and Quaeyhaegen and Knuyt [9] have introduced the first approaches to this geometry in term of residual macro-stress measurement. Using this method the non-destructive analysis of the residual stresses for different penetration depth bellow the sample surface can be performed. The problems concerning penetration depth, diffraction intensity distribution, Copyright(c)JCPDS-International Centre for Diffraction Data 2001,Advances in X-ray Analysis,Vol.44 1 134