Papers by Keyword: Residual Stress Gradient

Abstract: In this research work, Ti/TiAlN multilayers of various designs were deposited on substrates pretreated by nitriding and etching procedures. The influence of the multilayer design on residual stress depth profiles was systematically analyzed for multilayers with different Titanium interlayer thicknesses. The depth dependency of stress was measured by a modified sin2ψ method, using various defined gracing incident angles and measuring angles that ensure constant penetration depths. The residual stresses were investigated by synchrotron X-ray diffraction (SXRD) at the HASYLAB at DESY in Hamburg, Germany. SXRD allows a phase specific stress evaluation of the ceramic and metallic layers of the multilayer systems and the adjacent substrate region. This investigation reveals an influence of the Ti layer thickness on the values and the slope of the residual stress profile in ceramic TiAlN layers.

Abstract: The paper deals with methods for X-ray stress analysis (XSA), which allow for the evaluation of near surface in-plane residual stress gradients σ_||(τ) and σ_||(z) in the LAPLACE- and the real space, respectively. Since the ‘robustness’ of residual stress gradient analysis strongly depends on both, the quality of the measured strain data and the number of experimental data points, the discussion aims at those approaches which are based on processing various diffraction lines or even complete diffraction patterns. It is shown that these techniques, which were originally developed for angle-dispersive (AD) diffraction, can be adapted and enhanced for energy-dispersive (ED) diffraction employing high-energy synchrotron radiation. With the example of a shot-peened ferritic steel it is demonstrated, that sin²ψ-data measured in the Ψ-mode of XSA employing the ED diffraction technique can be analyzed on different levels of approximation.

Abstract: Residual stress depth profiling can be performed by means of non-destructive diffraction methods as well as semi destructive mechanical techniques like the hole drilling method. By none of these methods is it possible to cover the complete depth range being affected by residual stress fields which extend from the surface into the volume of the material. In this paper it is demonstrated that the combined application of surface sensitive X-ray methods and neutron diffraction used normally for bulk stress analysis allows for the study of residual stress gradients generated by mechanical surface treatment. Furthermore, it is shown that the hole drilling method can bridge the information gap between X-ray and neutron diffraction.

Abstract: Roughness influence on the residual stress gradient evaluation in the case of a grazing incidence X-ray diffraction setup is considered. In this geometry the surface roughness changes essentially the X-ray wave fields of the transmitted and diffracted beams inside the coatings and subsurface regions of bulk samples, and thus influences the refractive properties of the investigated sample area. In turn, the change in the refraction index enforces the re-scale of the informational depth and, consequently, the evaluated stress depth profile. The diffracted amplitude from the crystalline grain located beneath the surface is calculated. The surface roughness is shown to contribute into reconstruction of the real stress gradient profile of the coating.

Abstract: Laser shock processing (LSP) is a new and competitive technology in comparison with classical mechanical surface treatments for alloys strengthening. The compressive residual stress could be induced by LSP, which further significantly affects materials surface properties. Aluminum based alloy 6056 is used for aeronautic components and their surface strengthening is very important to increase components’ durability. The main factors of LSP, which affect the surface properties of alloys, such as surface roughness and residual stress gradient, are studied and analyzed in present study. The sin2* method with pseudo-grazing incidence X-ray diffraction (GIXRD) is used to determine the residual stress gradient after LSP treatment. In addition, the FEM simulation of residual stress distribution induced by LSP is also carried out and the results are compared with experimental data.