—The grain-boundary diffusion of Co in Nb has been studied by a layer-by-layer radiometric analysis in the temperature range of 723–873 K. The diffusion annealing modes corresponded to the kinetic C mode, which implies that the diffusion proceeds only along grain boundaries. The coefficients of grain-boundary diffusion of Co in Nb have been determined for several temperatures from diffusion profiles. An expression for the Arrhenius dependence of Co diffusion coefficient along the grain boundaries of Nb has been determined. The temperature dependence of coefficient of grain-boundary segregation of Co in Nb is constructed based on the temperature dependence of coefficient of grain-boundary diffusion of Co in Nb and the data in the literature on the temperature dependence of the triple product.

Grain boundaries in ultrafine-grained niobium deformed by high-pressure torsion have been studied by Mössbauer emission spectroscopy on 57Co(57Fe) nuclei. The evolution of the grain boundary state upon heating has been studied. Grain boundaries have been shown to be in a “nonequilibrium” (deformation-modified) state, which is characterized by an excess free volume, after severe plastic deformation. Annealing changes the state of grain boundaries, bringing them closer to the state characteristic of coarse-grained materials.

The grain structure of tin bronze with 7.4 wt % Sn after high-pressure torsion (HPT) at room temperature and subsequent annealing is analyzed.It is demonstrated that, in Cu-7.4 % Sn bronze, two groups of grains with different characteristics and different grain-boundary mobility are formed under deformation by HPT.It can be stated that the formation of two groups of grains results from different inclination of grains to relaxation due to the presence of competitive processes occurring directly under deformation.The grains of both groups evolve under heating, with increasing average crystallite size as the annealing temperature rises; however, their volume fraction depends on the defectiveness of the crystallites themselves.

The effect of high-speed dynamic compression on the structure and mechanical properties of low-alloyed tin bronze in different initial states (coarse-grained, with additional annealing, and cast, obtained by spun casting) and commercially pure copper of the M1 standard is investigated.The results obtained show that the dynamic compression of tin bronze samples in the coarse-grained initial state causes intensive twinning starting from a strain rate of 2.6•10 3 •s -1 .At relatively low deformation rates, the dynamic compression of samples in the initial cast state promotes an increase in their strength characteristics, whereas, with a further strain rate increase, the development of relaxation processes is observed.However, additional homogenization annealing decreases the probability of relaxation processes under loading, which results in the highest possible mechanical characteristics.The studies of the M1 commercially pure copper have shown that variations in the deformation rate much less affect the properties than in case of bronze, and their values are lower due to relaxation processes both under loading and after deformation.

The evolution of the structure of Cu-1Sn tin bronze under severe plastic deformation by high-pressure torsion has been studied and compared with that of commercially pure copper.It is demonstrated that high-pressure torsion of bronze results in much higher strengthening and structure refinement than that of commercially pure copper, as the presence of the doping element in the former promotes the retardation of dynamic recrystallization and relaxation processes.Besides, contrary to copper, which undergoes not only dynamic, but also post-dynamic recrystallization, all the bronze samples studied are stable after the HPT at room temperature, and they do not suffer any changes after unloading and prolonged ageing.