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. The various analysis methods and measurement strategies, in dependence on specimen and measurement conditions, are summarized and evaluated in this paper. First, different X-ray diffraction geometries (conventional or grazing incidence) are described. 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. The treatment is organized according to the number of unknowns to be determined (i.e. the state of stress, principal axes known or unknown), the use of one or several values of the rotation angle ' and the tilt angle of the sample, and one or multiple hkl reflections. Next, the focus is on macroscopically elastically anisotropic (e.g. textured) specimens. In this case, the use of diffraction (X-ray) elastic constants is not possible. Instead, diffraction (X-ray) stress factors have to be used. On the basis of examples, it is demonstrated that successful diffraction stress analysis is only possible if an appropriate grain-interaction model is applied.

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By X-ray diffraction and neutron diffraction using the isotopic substitution method, the partial structure factors /S

The atomic structure and phase separation of amorphous Si-B-C-N ceramic powder samples obtained by thermolysis of boron-modified polysilazanes were investigated using X-ray and neutron diffraction in the wide-angle and small-angle scattering regimes. The short-range order of the Si-B-C-N ceramics corresponds to that of Si-C-N ceramics consisting of two separated amorphous phases: an amorphous graphite-like phase and amorphous Si 3+(1/4)x N 4-x C x (x ) 0-4). The evaluation of the total pair correlation functions revealed that the boron atoms are bonded to nitrogen with B-N bond lengths typical for h-BN. These units are incorporated in the graphite-like phase not statistically, but within regions of BN-rings which are less extended than the regions formed by C-rings. X-ray diffraction phase analysis and small-angle scattering showed that the addition of up to 10 at. % of boron to Si-C-N ceramics significantly influences the high-temperature behavior of the ceramics: coarsening of the separated amorphous phases, the crystallization of Si 3 N 4 and its decomposition are retarded, and evolution of a nanocrystalline SiC phase is observed.

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