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A comprehensive study was performed of the deformation and temperature behavior during quasi-static tension, as well as the peculiarities of accumulation and dissipation of energy during plastic deformation. Microstructural analysis at the pre-fracture stage of pure titanium and Ti-45Nb alloy in the coarse grain (CG) and ultrafine-grained (UFG) states was also conducted. It was shown that substructural and dispersion hardening leads to a change in the regularities of dissipation and accumulation energies during deformation of the samples of the pure titanium and Ti-45Nb alloy in the UFG state. Some features of structural transformations during deformation of the pure titanium and Ti-45Nb alloy samples in the CG and UFG states were studied. A band and cellular-network and fragmented dislocation structure was formed in the case of the CG state, while large anisotropic fragments were formed in the UFG state, thus specifying a local softening of the material before fracture.

The paper presents the results of fatigue-testing ultrafine-grained and coarse-grained Ti-45 wt.% Nb alloy samples under very high cycle fatigue (gigacycle regime), with the stress ratio R = −1. The ultrafine-grained (UFG) structure in the investigated alloy was formed by the two-stage SPD method, which included multidirectional forging (abc–forging) and multipass rolling in grooved rollers, with further recrystallization annealing. The UFG structure of the Ti-45 wt.% Nb alloy samples increased the fatigue limit under the high-cycle fatigue conditions up to 1.5 times compared with that of the coarse-grained (CG) samples. The infrared thermography method was applied to investigate the evolution of temperature fields in the samples under cyclic loading. Based on numerical morphology analysis, the scale invariance (the Hurst exponent) and qualitative differences for UFG and CG structures were determined. The latter resulted from the initiation and propagation of fatigue cracks in both ultra-fine grained and coarse-grained alloy samples under very high-cycle fatigue loading.

The evolution of the microstructure and mechanical properties (for example, microhardness) of biodegradable alloy Mg−0.8 wt % Ca after multi-pass rolling in grooved rollers at different accumulated strain values e = 0.4, 0.9, 2.0 was investigated. As a result of multi-pass rolling under cumulative deformation e = 2.0, the recrystallized structure with average grain size of 1.4 µm and ultrafine grain volume ratio of up to 35% were formed in the alloy. It was proved that the absence of alloy strengthening after rolling was associated with the fact that the strengthening due to grain size refinement was compensated by annealing, as a result of dynamic recovery. This also resulted in further redistribution of the phase composition with decreasing volume ratio and Mg2Ca particle dispersion.

The method of grain refinement is described which is used to obtain titanium and zirconium base alloys in an ultra-fine grain state. The method involves abc-press forging and subsequent multiple-pass die rolling. It is shown that annealing performed at temperatures below the recrystallization threshold would cause formation of a stable nanostructure. The characteristics of such nanostructure would remain unaffected even at high plastic deformation levels until the fracture of the object made from this material. Both alloys having nanostructure are suitable for medical applications.

This paper focuses on the development of the microstructure and mechanical properties of bioinert Ti-40 wt.% Nb alloy after severe plastic deformation. Primary Ti40Nb cast billets were exposed to a combined two-stage severe plastic deformation method, including abc-pressing and multi-pass rolling in grooved rollers. It was proved that a relatively large amount of micron grains and subgrains were produced from the alloy through severe plastic deformation (SPD) method. Local shear zone, twins and low-angle grain boundaries were created in meantime. The misorientation angles of less than 6.45° constitutes 53.8 % of the alloy. SPD method intensified the formation of ultrafine-grained structure in Ti40Nb billet bulk with average element size of 0.3 µm. This, in its turn, improved the material strength. Microhardness of the alloy increased from 1730 MPa to 3000 MPa.

The results of studies on the deformation behavior during quasistatic tension of zirconium-based alloy samples (Zr-1 wt.% Nb) in microcrystalline and ultrafine-grained states are presented. The patterns of strain field distributions on the surface of the samples under tension have been obtained using a three-dimensional digital optical system Vic-3D. It has been established that the deformation difference in the plastic strain zone relative to the deformation, averaged over the entire sample, depends on the structural state of the Zr-1Nb alloy at the stage preceding destruction of the samples. Based on the analysis of the distribution patterns of strain fields, the Poisson’s ratio and the Gruneisen parameter in the plastic strain zone have been determined.

Fatigue testing of ultrafine-grained, fine-grained and coarse-grained VT1-0 and Zr–1 wt. % Nb samples was performed under conditions of gigacycle fatigue regime. It was established that ultrafine-grained titanium and zirconium alloy samples initiate increasing fatigue strength of up to 1.3 times for titanium and 1.7 times for zirconium alloy within gigacycle region (109 cycles) comparable to fine-grained and coarse-grained samples. Analysis of fracture surface morphology has revealed the similar fractured structure in coarse-grained and ultrafine-grained titanium and zirconium alloy samples. Fractures in ultrafine-grained titanium and zirconium alloy samples exhibit quasi-brittle pattern.

The paper presents the experimental data observed in the microstructure and phase composition of ultrafine-grained Ti–40 mass % Nb (Ti40Nb) alloy after high-temperature annealings. The ultrafine-grained Ti40Nb alloy is produced by severe plastic deformation (SPD). This method includes multiple abc-pressing and multi-pass rolling followed by further pre-recrystallizing annealing which, in its turn, enhances the formation of ultrafine-grained structures with mean size of 0.28 µm involving stable β- and α-phase and metastable nanosized ω-phase in the alloy. It is shown that annealing at 500°C preserves the ultrafine-grained structure and phase composition. In cases of annealing at 800°C the ultrafine-grained state transforms into the coarse-grained state. The stable β-phase and the nanosized metastable ω-phase have been identified in the coarse-grained structure.

The paper describes the experimental results in microstructure thermal stability and mechanical properties of ultrafine-grained zirconium alloy with 1 mass % Nb (Zr–1 mass %Nb) under prolonged thermal exposure. Ultrafine-grained zirconium alloy is produced by severe plastic deformation (SPD) method. It was proved that SPD method including multiple аbс-pressing and multi-pass rolling, as well as further pre-recrystallizing annealing enhances the formation of ultrafine-grained structures with mean element size of 0.2 µm. Thermostability time interval of ultrafine-grained structure and the mechanical properties (in case of microhardness) under prolonged thermal exposure (up to 360 hours) for zirconium alloy was experimentally determined. It was proved that ultrafine-grained structure is stable at 400°С within 10 hours whilst keeping the microhardness level attained after SPD. In cases of continuous annealing time from 24 to 360 hours recrystallization processes develop intensively, followed by the decrease i...

The study presents the analysis of microstructure, phase composition and mechanical properties of Ti40Nb alloy exposed to severe plastic deformation. It was shown that isothermal multi-axial forging and further multi-pass rolling intensify the formation of ultra-fine grained structure in the bulk of a billet with the average element size of 0.3 μm. Such ultra-fine grained structure considerably improves the alloy mechanical properties.