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Surface treatments characterized by rapid heating and cooling (e.g. laser hardening) can induce very steep residual stress gradients in the direct vicinity of the area being treated. These gradients cannot be characterized with sufficient accuracy by means of the classical sin2Ψ approach applying angle-dispersive X-ray diffraction. This can be mainly attributed to limitations of the material removal method. In order to resolve residual stress gradients in these regions without affecting the residual stress equilibrium, another angle-dispersive approach, i.e. the universal plot method, can be used. A novel combination of the two approaches (sin2Ψ and universal plot) is introduced in the present work. Prevailing limits with respect to profiles as a function of depth can be overcome and, thus, high-resolution surface layer characterization is enabled. The data obtained are discussed comprehensively in comparison with results elaborated by energy-dispersive X-ray diffraction measurements.

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Under laboratory conditions while applying angle-dispersive X-ray diffraction, the information depth in steel is usually restricted to less than 10 μm. Access to residual stresses induced by mechanical, chemical, or both types of surface treatment in deeper regions requires either the application of the layer removal method or an analysis with highly penetrating X rays and synchrotron radiation, respectively. Successive layer removal yields the actual residual stress depth profiles σij(z) up to any depth below the surface, but this is time consuming and semidestructive. High-energy X-ray diffraction performed in the energy-dispersive mode avoids these drawbacks, but it provides only the Laplace stresses, σij(τ), which have to be transformed back into the real space in order to obtain the actual stress-depth profile σij(z). Using an example of a uniaxially ground steel specimen, it is shown that the layer removal method and the energy-dispersive diffraction method for X-ray stress analysis when performed in reflection geometry yield comparable results in the case of the in-plane stress components σ11 and σ22. However, significant differences were observed concerning the out-of-plane stresses, which can be attributed to the boundary conditions that the σi3 components must satisfy at the free surface. It is demonstrated that stress redistribution at the newly generated surfaces after successive layer removal leads to an underestimation of the shear stresses σ13. The analysis of the out-of-plane normal stress component σ33 is shown to require nondestructive measurements.

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