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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.

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 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.