G. P. Pochivalova

True grain-boundary slipping in coarse- and ultrafine-grained titanium

The temperature dependence of internal grain-boundary friction in coarse- and ultrafine-grained titanium is investigated. It is demonstrated that true grain-boundary slipping causes internal grain-boundary friction in ultrafine-grained titanium, as in coarse-grained metals. It is established that when going from the coarse-grained structure with perfect grain boundaries to ultrafine-grained structure with imperfect grain boundaries, the temperatures of the beginning and intense development of true grain-boundary slipping decrease together with the activation energy of this process. The diffusion mechanism of true grain-boundary slipping is justified for both structural states.

Structure and mechanical and electrochemical properties of ultrafine-grained Ti

A study is conducted into the microstructure and physico-mechanical properties of ultrafine-grained titanium produced by severe plastic deformation using the method of equichannel angular pressing. The effects of thermal and mechanical treatment on these characteristics are investigated. The possibility of forming mechanical properties in titanium that compare well with those of highly doped titanium alloys is shown.

Microplastic deformation of polycrystalline and submicrocrystalline titanium during static and cyclic loading

A study is made of the laws governing the accumulation of microplastic strain during the static and cyclic loading of polycrystalline and submicrocrystalline titanium. It is shown that a change from the polycrystalline structure to the submicrocrystalline structure does not change the character of development of microplastic strain for either type of loading, but it does increase fatigue strength and fatigue limit. A correlation between the fatigue strength based on 106 cycles and the macroscopic elastic limit was found to exist for both types of loading.

Microplastic deformation of polycrystals during cyclic loading

A model of microplastic deformation of polycrystals during zero-start cyclic loading with tensions lower than the yield strength is proposed according to which during cycling, thermally activated movement of dislocations occurs under conditions of stress relaxation. Based on this model and the statistical theory of polycrystalline microdeformation, the accumulation of microplastic deformation is theoretically described as a function of the number of loading cycles and the stress amplitudes. It is theoretically proved that in the cycling process the microplastic deformation that accumulates over one cycle decreases as the number of cycles increases; up to the macroscopic elastic limit it is independent of the stress amplitude, and then sharply increases. Agreement of the theory with experimental data for spring alloys is observed in the density of mobile dislocations, which decreases during cycling.

Stress relaxation in the region of microplastic deformation of polycrystals

Stress relaxation equations are derived to predict the relaxation capacity of a material on the basis of studies of microplastic deformation under static loading. The approach was checked experimentally on spring steels LANKMts, ÉI702, ÉP637, and 50KhFA.