OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 4 2022 obtained from the ingot as a result of pre-pressing. Abc-pressing of the billet was carried out with a step decrease in temperature from 500 to 400 °C. In this case, a single upsetting of the billet at each temperature was performed. Rolling of preheated billets to 200 °C was carried out, as in the case of the first scheme, at the room temperature of the rolls. In this case, the total logarithmic degree of deformation was 2.94. After the application of the first and second schemes, plates with dimensions of 10×1.5×140 mm3 were obtained. The prepared samples were annealed at 350 °C for one hour in an argon atmosphere and then cooled with the furnace to remove residual internal stresses and to increase plasticity. For a comparative study of UFG states with a CG structure, we used recrystallization annealing of a part of the samples at 800 °C for one hour after the second scheme of deformation. The microstructure and phase composition of the samples were studied using optical microscopy (Carl Zeiss Axio Observer microscope), transmission electron and scanning electron microscopy (JEOL JEM 2100 and LEO EVO 50 microscopes), as well as X-ray diffractometry (DRON-7 diffractometer). The X-ray diffraction patterns were obtained in CoKα radiation. The average size of structural elements (grains, subgrains, fragments) was calculated using the secant line method [14]. The microhardness was measured using the Duramin 5 microhardness tester. The mechanical tensile tests were performed on the Instron 5582 testing machine. During mechanical testing, five samples were used for each state. The elastic modulus was determined using the DUH-211S Nano Hardness Tester by pressing the indenter into the surface of the sample with simultaneous plotting of the “stress–strain” kinetic diagram. The microstructural and X-ray diffraction studies, as well as measurements of microhardness and mechanical tests of the samples were carried out for the CG state and for the UFG states obtained after rolling and after combined deformation impact (abc-pressing and rolling). Results and discussion Fig. 2, a, b shows the microstructure of the Ti-42Nb-7Zr ingots after remelting. The microstructure is heterogeneous across the cross-section of the ingot in the cast state. Three zones are readily observed. The first zone consists of equiaxed grains. The second and third zones have a dendritic structure, where the second zone is region with a cellular structure, and the third zone is a region of elongated columnar dendrites. Fig. 1. Scheme of heat and deformation treatments of Ti-42Nb-7Zr alloy
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