Development of ultrafine-grained and nanostructured bioinert alloys based on titanium, zirconium and niobium and their microstructure, mechanical and biological properties

For this paper, studies of the microstructure as well as the mechanical and biological properties of bioinert titanium, zirconium, and niobium alloys in their nanostructured (NS) and ultrafine-grained (UFG) states have been completed. The NS and UFG states were formed by a combined two-step method of severe plastic deformation (SPD), first with multidirectional forging (MDF) or pressing into a symmetrical channel (PSC) at a given temperature regime, and then subsequent multi-pass groove rolling (MPGR) at room temperature, with pre-recrystallization annealing. Annealing increased the plasticity of the alloys in the NS and UFG states without changing the grain size. The UFG structure, with an average size of structural elements of no more than 0.3 mu m, was formed as a result of applying two-step SPD and annealing. This structure presented significant improvement in the mechanical characteristics of the alloys, in comparison with the alloys in the coarse-grained (CG) or small-grained (SG) states. At the same time, although the formation of the UFG structure leads to a significant increase in the yield strength and tensile strength of the alloys, their elastic modulus did not change. In terms of biocompatibility, the cultivation of MG-63 osteosarcoma cells on the polished and sandblasted substrates demonstrated high cell viability after 10 days and good cell adhesion to the surface

Influence of severe plastic deformation by extrusion on microstructure, deformation and thermal behavior under tension of magnesium alloy Mg-2.9Y-1.3Nd

The microstructural investigation, mechanical properties, and accumulation and dissipation of energies of the magnesium alloy Mg-2.9Y-1.3Nd in the recrystallized state and after severe plastic deformation (SPD) by extrusion are presented. The use of SPD provides the formation of a bimodal structure consisting of grains with an average size 15 µm and of ultrafine-grained grains with sizes less than 1 µm and volume fractions up to 50%, as well as of the fine particles of the second Mg24Y5 phases. It is established that grain refinement during extrusion is accompanied by an increase of the yield strength, increase of the tensile strength by 1.5 times, and increase of the plasticity by 1.8 times, all of which are due to substructural hardening, redistribution of the phase composition, and texture formation. Using infrared thermography, it was revealed that before the destruction of Mg-2.9Y-1.3Nd in the recrystallized state, there is a sharp jump of temperature by 10 ◦C, and the strain hardening coefficient becomes negative and amounts to (−6) GPa. SPD leads to a redistribution of thermal energy over the sample during deformation, does not cause a sharp increase in temperature, and reduces the strain hardening coefficient by 2.5 times

Influence of Zr-1 wt.% Nb alloy structure state on its deformation and thermal behavior under quasi-static tension

The influence of the average size of the structure elements on the deformation and thermal behavior of the Zr-1 wt.% Nb (Zr1-Nb) alloy under quasi-static tension was investigated using the digital image correlation and infrared thermography methods. It is shown that with increasing average size of the structural elements in the range 0.2–2.0 mm the physico-mechanical properties, such as yield strength, microhardness, maximal true strain, and maximal temperature increment during deformation decrease, while longitudinal and transverse strain increase. According to the obtained results, correlations between the mentioned deformation characteristics and the average size of the structural element d–1/2 can be described by linear functions