Exploiting the advantages of energy‐dispersive synchrotron diffraction, a method for the determination of strongly inhomogeneous residual stress depth gradients is developed, which is an enhancement of the stress scanning technique. For this purpose, simulations on the basis of a very steep residual stress depth profile are performed, and it is shown that conventional real space evaluation approaches fail, because they do not take into account the variation of the residual stresses within the gauge volume. Therefore, a concept facilitating the deconvolution of the diffraction signal by considering the effect of the gauge volume geometry as well as the influence of the material absorption on the average information depth is proposed. It is demonstrated that data evaluation requires a three‐dimensional least‐squares fit procedure in this case. Furthermore, possible aberrations and their impact on the analysis of the residual stresses by applying the `modified stress scanning' method are treated theoretically.
The modified stress scanning method [http://scripts.iucr.org/cgi-bin/paper?to5114] is experimentally implemented for the analysis of near‐surface residual stress depth distributions that are strongly inhomogeneous. The suggested procedure is validated by analyzing the very steep in‐plane residual stress depth profile of a shot‐peened Al2O3 ceramic specimen and comparing the results with those that were obtained by well established X‐ray diffraction‐based gradient methods. In addition, the evaluation formalism is adapted to the depth‐dependent determination of the residual stresses inside of multilayer thin‐film systems. The applicability for this purpose is demonstrated by investigating the residual stress depth distribution within the individual sublayers of a multilayered coating that consists of alternating Al2O3 and TiCN thin films. In this connection, the specific diffraction geometry that was used for the implementation of the stress scanning method at the energy‐dispersive materials science beamline EDDI@BESSYII is presented, and experimental issues as well as limitations of the method are discussed.
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.
Recently, the ‘stress scanning method’ has been introduced in the field of depth resolved residual stress analysis. The principle of this method is based on depth scans that are performed in several inclination angles with a gauge volume characterized by a height dimension in the range of 10 µm. This method has been used in the energy-dispersive mode of diffraction for rather long-range depth gradients. In this case the variation of the residual stresses is negligible on the scale of the gauge volume height dimension. In this contribution it is shown that the stress scanning method can be extended to the analysis of steep residual stress depth gradients that vary significantly even within the height dimension of the gauge volume, but a careful evaluation of the measured data is necessary and must be adapted to the special case.
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