Study of substructural heterogeneity of textured materials by the X-ray method of generalized direct pole figures

Abstract

Any material can be considered a composite consisting of grains of different orientations which possess different properties depending on the history of their reorientation upon thermomechanical processing. A well-known selective character of X-ray methods is attributed to the fact that only grains of certain orientations participate in the formation of reflected radiation. A comprehensive description of the material including information about the substructure of grains of all orientations necessitates developing of the method providing description of the substructural state of grains located in the volume under study by analyzing the profile of x-ray lines. The proposed x-ray diffractometric method of Generalized Direct Pole Figures (GPF) which suggests combination of texture imaging and recording the profile of x-ray lines appeared to be rather efficient in a systematic x-ray study of the substructural heterogeneity of textured metallic materials. The measured parameters of the X-ray line profile — the true angular half-width β and angular peak position 2θ — are determined by the distortion (fragmentation) of the reflecting grains and interplanar spacings in their crystal lattice, respectively. The method provides a possibility to compare the substructure features of grains with different crystallographic orientations. An algorithm for calculation of the true physical half-width of the x-ray line using the necessary computer programs is presented. GPF β and GPF 2θ are presented for metal materials with hcp, fcc, and bcc crystalline lattices, as well as characteristic diagrams of their mutual correlation with texture PF. The use of the developed GPF method makes it possible to identify patterns of the formation of substructural heterogeneity during plastic deformation of metals.