Papers by Author: T.I. Savyolova

Abstract: Various equal channel angular pressing (ECAP) regimes by routes A and Bc were applied to a commercial MA2-1 (Mg-5wt.%Al-1wt.%Zn-0.4wt.%Mn) alloy for the development of texture which is different from the one of conventionally extruded and annealed alloy. In order to avoid the grain-size effect, the ECAP-processed alloy was annealed to coarsen the grains. The alloy texture before and after the ECAP was determined by the approximation of the X-ray measured pole figures with the canonical normal distributions of central type. The ECAP implementation results in the formation of ultra-fine grained structure of the alloy with an average grain size of 2.0-2.4 µm. The ECAP also drastically changes the initial axial texture characterized by a sharp basal component by splitting it into several more scattered orientations. The degree of the orientation scattering depends on the ECAP regime and route. The annealing of alloy after ECAP results in the grain size growth to the initial state of the extruded and annealed alloy. In addition to that the texture changes of the ECAP-processed alloy after annealing, unlike the structure changes, don’t result in texture of the initial state. The mechanical tensile properties of the annealed alloy substantially depend on the preceding ECAP routes. The yield strength of the annealed alloy decreases after all routes of ECAP. On the contrary, the uniform elongation compared with the one of the initial state of the alloy decreases after 4A route and increases after 4Bc route of ECAP. The effect of the texture and structure on the yield strength and tensile elongation of the alloy after ECAP and annealing was estimated using calculation of the generalized Schmid factors for specific preferred orientations of the active deformation systems and Hall-Petch relationship.

Abstract: Influences of an X-ray experimental texture plan and of pole figure primary errors on the accuracy of the ODF coefficients are discussed. A modified harmonic method, which is a statistical method of ridge estimates, has been used for ODF restitution from pole figures. The plan of measurement of the pole figures was analysed on the basis of minimization of the primary experimental errors and the errors of the ODF restitution method. Principles of the optimum texture plan construction for hexagonal metals (magnesium example) and for the URD-6 texture diffractometer are considered.

Abstract: The mathematical method of the texture function restoration according to diffraction experiment is offered. The texture function is represented as superposition of standard texture functions with the identical dispersions, located on a regular three-dimensional grid in orientation space. Applicability of the method is shown by model examples and in an example of a cold rolled texture of a copper sheet.

Abstract: Experimental pole figures are measured by x-ray method for materials with hexagonal symmetry (Ti and Mg alloys). The Orientation Distribution Function is calculated by approximation method with central normal distribution. Texture inhomogeneities and effects of defocusing are the main sources of pole density errors. The measurement errors depend on crystal direction {hkl} and are different for maximum and minimum regions on pole figure. The influence of texture measurement errors on accuracy of the ODF calculation is investigated.

Abstract: A new method of computing of normal distributions [1] on rotation groups is suggested. Monte Carlo method allows to calculate the orientation of grains function (ODF) and correspondent pole figures (PFs) using approximation by normal distributions [2]. The developed Monte Carlo method is applied for construction of PFs mathematical statistical model corresponding to experimental measurement. This model is based on statistical simulation of normal distributions on SO(3) group for discrete representation of pole figures. It is possible to calculate effective physical properties of polycrystals using the given discrete representation. The mathematical simulation for texture with two components of polycrystalline sample with hexagonal symmetry is developed. Two experimental PFs } 0 1 10 { and } 0002 { for Be measured by X-ray experiment are being used. For this case the effective property as a tensor of elastic compliance was calculated. The mathematical simulation of PFs also allows to determine the statistical errors of pole figures measurement.