Inspection of the existing literature shows that earlier reviews are either incomplete or superficial, in particular in view of the indicated new developments. ![]() The listing is not complete but embodies a representative collection. ceramics, metals or polymers), have been included. ![]() reviews not only dedicated to a certain class of materials ( e.g. New developments dedicated to the stress analysis of thin films and surface layers are a focal point of interest in this review paper.Ī selection of reviews on X-ray diffraction stress analysis in the past 25 years is given in Table 1. Thus, standard methods of analysis applicable to bulk aggregates may fail when applied to the stress analysis of thin films (see, for example, van Leeuwen et al., 1999 Leoni et al., 2001 Welzel et al., 2003 Welzel, Leoni & Mittemeijer, 2004 ). However, dedicated diffraction geometries for films much thinner than the X-ray penetration depth have been developed in the past few years and thin films are frequently mechanically elastically anisotropic due to the occurrence of crystallographic texture and/or direction-dependent grain interaction 1 (Welzel & Mittemeijer, 2003 ). In principle, no distinction exists between the analysis of stress in bulk materials and in thin layers. Moreover, useful additional information can be obtained as a by-product of X-ray diffraction stress measurements: whereas the stress analysis uses the shifts of diffraction lines, the (integral) intensities of diffraction lines contain information on the crystallographic texture (see, for example, Bunge, 1982 ), and the shapes and breadths of diffraction lines contain information on the size (distribution) of diffracting domains and the content of crystalline defects such as dislocations and stacking faults (see, for example, Delhez et al., 1982 ). X-ray diffraction methods allow a determination of the full mechanical stress tensor of all crystalline phases furthermore, the analysis of stress gradients is feasible. The rather limited penetration depth of (such) X-rays in solid matter results in surface sensitivity. If, on the other hand, a film or surface layer can be pre-stressed during its production, a compressive pre-stress may prevent cracking when stresses resulting from external forces occur during service life.Īmong a number of methods available for stress analysis, X-ray diffraction methods employing the characteristic radiation emitted from an X-ray tube or medium-energy synchrotron radiation ( E = 5–15 keV) are very suitable for the analysis of films and surface layers. As an example, stress can result in cracking of a film in the case of tensile stress, or buckling in the case of compressive stress. The analysis of the residual stress state is of great technological importance because stresses can be beneficial or detrimental with respect to, in particular, the mechanical properties (see, for example, Hauk, 1997, §6 therein). In thin films and regions near the surface of bulk materials, residual stresses are generally present (see, for example, Hoffman, 1966, 1976 Windischmann, 1992 Machlin, 1995 Proceedings of the International Conference on Residual Stresses, Proceedings of the European Conference on Residual Stresses). On the basis of examples, it is demonstrated that successful diffraction stress analysis is only possible if an appropriate grain-interaction model is applied. Instead, diffraction (X-ray) stress factors have to be used. In this case, the use of diffraction (X-ray) elastic constants is not possible. Next, the focus is on macroscopically elastically anisotropic ( e.g. the state of stress, principal axes known or unknown), the use of one or several values of the rotation angle φ and the tilt angle ψ of the sample, and one or multiple hkl reflections. ![]() The treatment is organized according to the number of unknowns to be determined ( i.e. Then, the case of macroscopically elastically isotropic, untextured specimens is considered: from the simplest case of a uniaxial state of stress to the most complicated case of a triaxial state of stress. First, different X-ray diffraction geometries (conventional or grazing incidence) are described. The various analysis methods and measurement strategies, in dependence on specimen and measurement conditions, are summarized and evaluated in this paper. The components of the macroscopic mechanical stress tensor of a stressed thin film, coating, multilayer or the region near the surface of a bulk material can in principle be determined by X-ray diffraction.
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