Non-destructive phase analysis and residual stresses measurement due to grazing angle X-ray diffraction geometry

S. J. Skrzypek¹, J. Jeleńkowski², W. Ratuszek¹, T. Wierzchoń²

¹Faculty of Metallurgy and Materials Science, University of Mining and Metallurgy,
Al. Mickiewicza 30, 30-059 Kraków, Poland,

e-mail:skrzypek@uci.agh.edu.pl, fax: (48) 12 6173190

²Faculty of Materials Science, University of Technology, 02-507 Warszawa,

ul. Wołoska 141

The non destructive structure characterisation of surface layers for various kind of fatigue experiments and machining of heat-treated steels and stainless steels or other materials having metastable phase can be a powerful tool in surface engineering. These kinds of treatments can cause phase transformation and/or non-uniform plastic deformation in surface layer. It is connected with volume change and non-uniform elasto-plastic deformation, which create residual macro and/or micro-stresses. These characteristics are gradient-like in mostly similar cases.

An application of classical X-ray diffraction sin²y method and classical Bragg-Brentanno diffraction geometry in these kinds of examinations make some problems in term of X-ray real depth of penetration. The Bragg-Brentanno diffraction geometry is characterised by parallel diffracting crystallographic plains {hkl} to the surface and non-linear increase of effective depth of X-ray penetration when Bragg angle (q) increases, contrary when sin²y method is used. An application of g-sin²y method which is based on grazing angle X-ray diffraction geometry made possible to get real value of residual macro-stresses and additionally could be suitable in estimation of their gradient-like distribution. An application of this geometry to X-ray diffraction phase analysis enabled to get phase contents versus thickness under surface in non-destructive way.

Surface preparation is usually demanded treatment like grinding and/or polishing before coating deposition. The grinding and polishing of austenitic steel can cause phase transformation of austenite and non-uniform plastic deformation in surface layer.

The X-ray quantitative phase analysis was used to establish volume fraction of transformed austenite. Theoretical calculation of residual macro-stresses due to volume fraction of transformed austenite in stainless steel and following measurements of residual stresses were curried out as well.

Grinding and polishing of samples caused big compressive residual stresses and phase transformation of austenite in thin surface layer. These factors can influence on properties of following deposited coatings.