GEOMETRY OF DIFFRACTION AND EFFECTIVE DEPTH OF PENETRATION IN RESIDUAL STRESS MEASUREMENT

S. J. Skrzypek

University of Mining and Metallurgy-AGH, Faculty of Metallurgy and Materials Science, 30-059 Kraków, al.Mickiewicza 30, Poland

The surface, thin films and coatings of engineering components play a key role in their quality by influence on final properties. The surface and near by its region is characterised by its phase composition, surface tension, viscosity, energy, residual stresses and mechanical features like roughness, waveness etc.

Residual stress (RS) becomes more and more important property of the surfaces and coatings because of their influence on their properties. This is for the reason of its superposition with loading and important influence of RS on physical, chemical structural and microstructural phenomena e.g. stress-induced phase transformation, piezoelectricity, linear relation of resistivity vs. RS and stress-induced self-disintegration etc.

Residual stresses usually examinied by X-ray diffraction with Bragg-Brentano geometry using y or w goniometers. Depth penetration zone for this case is changed versus theta (q) and y angles. This is particularly important for coatings and surface layers with big gradients of RS. New geometry i.e. grazing angle scattering geometry avoids above inconvenience. Although most methods of measurements of residual stresses are still under development they become more and more accurate. Gradients of RS and change of effective depth of penetration are important sources of measurement errors. The new version of sin²y method due to grazing angle scattering geometry marked g-sin²y was applied to residual macrostresses of TiN coatings.