Ch. Genzel

A self-consistent method for X-ray diffraction analysis of multiaxial residual-stress fields in the near-surface region of polycrystalline materials. II. Examples

The application of the formalism for residual-stress gradient evaluation based on the measuring principle of the scattering-vector method, which has been derived in the first paper of this series [Genzel (1999). J. Appl. Cryst. 32, 770–778], is demonstrated by practical examples. Depending on the statistical scattering of the experimental data, either biaxial or even triaxial residual-stress states may be analysed; the latter case yields self-consistently the depth profiles of the in-plane stresses, σ11(τ) and σ22(τ), the normal stress component, σ33(τ), as well as the strain-free lattice spacing, d0(hkl). The results obtained by this new evaluation procedure are compared with those obtained by X-ray stress-gradient analysis performed on the basis of the sin2ψ method.

Stress in undoped and doped laser crystallized poly-Si

Raman measurements were performed on laser crystallized poly-Si on different substrates. Observed shifts of the Si LO–TO phonon peak are caused by stress originating from the film-substrate interface. The principal cause of the stress is the difference in the thermal expansion coefficients of substrate and film. Consequently, the amount of thermal stress critically depends on the choice of substrate. In the case of undoped samples on quartz, profiler and x-ray measurements confirmed the occurrence of tensile stress in the films. In the case of heavily doped samples, the change of the lattice parameter determined by x-rays is probably to a significant extend responsible for additional Raman shifts.

Some new aspects in X-ray stress analysis of thin layers

Abstract Due to their influence on the mechanical properties, residual stresses in thin hard coatings and their non-destructive analysis by X-ray diffraction have become an important topic in materials science. Because it is possible today to achieve defined internal stress gradients with respect to the layer thickness by appropriate variation of the deposition parameters, the applied diffraction methods have to meet the demand for a depth-resolved stress evaluation. By the example of thin PVD coatings of Ti1−xCrxN with a marked 〈111〉 fibre texture, the paper compares several methods in X-ray stress analysis (XSA) concerning their suitability for the detection of stress gradients in thin layers. The best results are obtained by means of the scattering vector method, where the lattice spacing depth profiles, d ϕ ψ ( h k l , τ ) , are measured after stepwise rotation of the sample around the scattering vector g ϕ ψ near the intensity poles of the texture.

Energy‐dispersive diffraction stress analysis under laboratory and synchrotron conditions: a comparative study

For a feasibility study of energy-dispersive residual stress analysis under laboratory conditions, an X-ray diffractometer that has been operated so far in the angle dispersive diffraction mode was equipped with a commercial tungsten tube and an energy-dispersive solid-state germanium detector. Starting from systematic investigations to find the optimum configuration regarding geometrical resolution, measuring time and stability of the applied detector system, different materials were characterized with respect to the near-surface residual stress state. The results achieved with the modified laboratory equipment within reasonable measuring times are in good agreement with synchrotron measurements performed on the same samples. With the example of a shot-peened Al2O3 ceramic with a highly non-uniform near-surface residual stress distribution it is furthermore shown that the different size and shape of the diffracting gauge volume used for the laboratory and synchrotron measurements might have a significant influence on the experimentally obtained Laplace-space residual stress depth profiles σ||(τ).

Sin2ψ-based residual stress gradient analysis by energy-dispersive synchrotron diffraction constrained by small gauge volumes. II. Experimental implementation

On the basis of the theoretical concept for the use of small gauge volumes to study near-surface residual stress fields with high spatial resolution [Meixner, Klaus & Genzel (2013). J. Appl. Cryst. 46, 610–618], the experimental implementation of the approach is demonstrated. It is shown that specifically designed slit systems are required to avoid effects such as diffuse scattering at the slit blades and total external reflection, both giving rise to a reduced resolution. Starting from the characterization of the small gauge volume, practical guidance on how to control the alignment of the sample relative to the gauge volume for different geometrical conditions of energy-dispersive diffraction is given. The narrow-slit configuration as well as the formalism for data evaluation introduced in the first part of this series is applied to the analysis of a very steep in-plane residual stress gradient in a shot-peened Al2O3 ceramic sample. The results are compared with those obtained by means of a conventional wide-slit setup using the classical universal plot method for residual stress analysis on the one hand, and with the simulations performed in the first part on the other hand.

Sb-doping of ZnO: Phase segregation and its impact on p-type doping

The incorporation of antimony (Sb) in pulsed-laser deposited ZnO thin-films was investigated employing scanning electron microscopy, Raman spectroscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction (XRD) measurements. It is shown that an increase in the Sb concentration in the target leads to a significant deterioration of the sample structure which is accompanied by a decrease in the deposition rate. Furthermore, the dopant transfer factor depends strongly on the deposition temperature and exhibits a steplike behavior above 600 °C. XRD measurements clearly show that significant Sb–O phase precipitations occur. The implications of our data on p-type doping of ZnO are discussed.

Thermal residual microstresses in steel-NbC particulate composites studied by X-ray and neutron diffraction

During cooling of particle reinforced metal matrix composites (PMMCs) residual microstresses emerge owing to the different physical and mechanical properties of the metal matrix and the coarse quasi-ceramic hard phases. The thermal residual microstress state at the sample surface and in the bulk are analysed using X-ray diffraction and neutron diffraction methods, respectively. While the X-ray diffraction results reveal a strong influence of the sample preparation on the surface residual stress state the results obtained by neutron diffraction are in good agreement with theoretical considerations.

White-beam X-ray radioscopy and tomography with simultaneous diffraction at the EDDI beamline.

A set-up for simultaneous imaging and diffraction that yields radiograms with up to 200 frames per second and 5.6 µm effective pixel size is presented. Tomograms and diffractograms are acquired together in 10 s. Two examples illustrate the attractiveness of combining these methods at the EDDI beamline for in situ studies.

Residual stress analysis of diamond‐coated WC–Co cutting tools: separation of film and substrate information by grazing X‐ray diffraction

Chemical vapour deposition (CVD) of diamond surface layers is an effective way of improving the properties of cemented carbide cutting tools. Inadequate coating adhesion is one of the main issues and it may be affected by the residual stresses of the CVD diamond films. The most common methods for nondestructive residual stress analysis are based on X-ray diffraction. The present paper deals with the particular case of determining the residual stress state of thin CVD diamond layers deposited on cobalt cemented tungsten carbide (WC–Co) substrates. It will be shown that the application of the conventional sin2ψ method might lead to erroneous results, as a result of superimposing diffraction lines originating from cobalt and the diamond coating. An approach to separating information on the substrate and film, based on grazing conditions in the symmetrical Ψ mode of diffraction, is presented. The results, revealing large compressive stresses within the coating, are compared with those obtained by supplementary micro-Raman spectroscopy investigations.

Residual stress in nano-structured stainless steel (AISI 316L) prompted by Xe+ ion bombardment at different impinging angles

The effect of low energy (<1 keV) xenon (Xe+) ion bombardment on the residual stress of polycrystalline iron alloy (AISI 316L steel) is reported. The results take into account the influence of the ion incident angle maintaining constant all other bombarding parameters (i.e., ion energy and current density, temperature, and doses). The bombarded surface topography shows that ions prompt the formation of nanometric regular patterns on the surface crystalline grains and stressing the structure. The paper focalizes on the study of the surface residual stress state stemming from the ion bombardment studied by means of the “sin2 ψ” and “Universal Plot” methods. The analysis shows the absence of shear stress in the affected material region and the presence of compressive in-plane residual biaxial stress (∼200 MPa) expanding up to ∼1 μm depth for all the studied samples. Samples under oblique bombardment present higher compressive stress values in the direction of the projected ion beam on the bombarded surface. ...