作者: Marek Andrzej Kojdecki

摘要: A polycrystalline material may be considered as a set of crystallites. Since the crystallites have rather regular shapes, the assumption about the same shape is not far from physical reality for most polycrystals, especially powders. Such a system may be characterised in a statistical manner by two functions, the crystallite size distribution and the crystalline lattice strain distribution (for some materials other lattice distortions inside the crystallites, like stacking faults or dislocations, are to be considered additionally). The crystalline microstructure can be determined by investigating an X-ray diffraction pattern, what should be based on comparing an experimental pattern with a simulated one, derived from an appropriate physical model. Pure X-ray diffraction line profiles, containing information about crystalline microstructure, can be extracted from
experimental data. An important step in analysing them is the separation of contributions from crystallite shapes and sizes and from strains, enabling the proper determination of both distributions together with the estimation of prevalent crystallite shape. A model of polycrystalline material combined with a description of X-ray diffraction on it, making such an analysis possible, is
presented in this article. An approximate formula for separating both effects is based on results of computer simulation of pure X-ray diffraction line profiles from different crystalline powders, done under simplifying assumptions that the crystallites are prismatic or spherical, the size distribution is logarithmic-normal and the second-order strain distribution is normal.

107

作者: U. Welzel, Eric J. Mittemeijer

摘要: The so-called crystallite group (CGM) method, employed for diffraction stress analysis, involves that a possibly complex texture is approximated by a set of one or a few so-called ideal orientations. It has been shown that this approximation can lead to pronounced errors in the determined stress values. The range of applicability of the CGM has been investigated from a
theoretical point of view. Numerical simulations of diffraction strain measurements have been performed using orientation distribution functions representing textures of different strength and sharpness. Special emphasis has been put on the fibre-textured case.

131

摘要: A novel X-ray diffraction method, allowing the position resolved imaging of a polycrystalline specimen using the diffracted radiation, was applied for in situ investigation of recrystallization of cold-rolled copper. A large area of the specimen could be observed simultaneously, yielding information about nucleation and growth of many individual crystallites. The recrystallization process showed a stochastic behavior which can be described by the model of self-organized criticality.

689

作者: J. te Nijenhuis, M.J. Fransen, J.H.A. Vasterink

摘要: In this study a detailed analysis is given of the development of preferred orientations of polycrystalline diamond films, deposited from the gas phase using the combustion-flame assisted chemical vapor deposition technique, as a function of the amount of intentionally added nitrogen. The preferred orientations are studied using X-ray diffraction and are compared with the morphological changes of the sample surfaces. The role of nitrogen in the deposition process is discussed. Low amounts of nitrogen enhance the growth rate and lead from a randomly oriented layer successively to {011} and {001} fiber textures. Higher amounts of nitrogen deteriorate the growth; no preferred orientation is visible anymore.

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