Fatigue behavior of ultrafine-grained Ti–24Nb–4Zr–8Sn multifunctional biomedical titanium alloy

A multifunctional titanium alloy Ti–24Nb–4Zr–8Sn (wt%) was fabricated by warm swaging and rolling to get homogeneous microstructure with ultrafine-grained (UFG) β phase and nanostructured (NS) α phase, and their stress-controlled high cycle fatigue (HCF) and strain-controlled low cycle fatigue (LCF) behaviors were investigated in the study. The results showed that the UFG alloy exhibits much higher HCF strength than that of the hot-rolled alloy with coarse grains whereas its LCF endurance is worse slightly. This was explained by its stable microstructure originated from low homologous temperature being ∼0.15 of melting temperature and the improvement of phase stability by grain refinement and NS precipitations. The former leads to dynamic recovery instead of dynamic recrystallization occurring in other UFG materials while the latter results in comparable cyclic stress stability with the hot-rolled alloy. The study also found that the shear bands have an identical angle of ∼26° with the loading direction, which is independent of the strain ratios. Since the ductile UFG alloy has a nonlinear elastic deformation behavior with large recoverable strain, its LCF endurance is much better than those of other materials exhibiting linear elasticity and would be further improved by the depression of NS precipitation.