Kedrovskyi S. Structure formation and functional properties of alloys based on Zr, Hf, Cu-Al, Ti-Ni and their welding joints

The thesis is devoted to the study of potentially biocompatible nickel-free functional alloys based on elements of groups IV and V of the periodic system of chemical elements and the effect of recrystallization on the properties of alloys based on Cu-Al, Ti-Ni and Zr-Nb systems. The effect of valence electrons concentration on the martensitic transformation in alloys of Group IV metal elements (Ti, Zr, Hf) with niobium and their relationship with functional properties are analyzed. It was found that an increase of the valence electrons concentration in all studied alloys leads to a decrease of the MT characteristic temperatures. To estimate the maximum concentration of Nb, at which the existence of the MT in alloys of the Zr-Nb and Hf-Nb systems is possible, computer simulations have been carried out. In some quenched alloys of the Zr-Nb, Hf-Nb, Zr-Ta, Zr-Nb-Ta systems, the presence of SME has been revealed for the first time. MF in these materials after quenching exists in wide temperature and concentration ranges. However, in zirconium alloys, with the addition of ~ 10 at.% of alloying components, the functional properties are suppressed by the formation of the ω-phase. New results of studying the effect of recrystallization processes during welding on the parameters of martensitic transformation in alloys based on the Cu-Al, Ti-Ni and Zr-Nb systems have been obtained, that significantly expands the designing possibilities of welded products for industrial and medical purposes that require joining. Variants of homogeneous and dissimilar joining of alloys based on Cu-Al have been investigated. It was found that the retention of functional properties in the recrystallized region is observed only in alloys based on the Cu-Al and Ti-Ni systems.