Impact Toughness of Ultrafine‐Grained Commercially Pure Titanium for Medical Application

Abstract

This study aims at achieving the best combination of strength, ductility, and impact toughness in ultrafine-grained (UFG) Ti Grade 4 produced by equalchannel angular pressing via Conform scheme (ECAP-C) with subsequent cold drawing. UFG structures with various parameters (e.g., size and shape of grains, dislocation density, conditions of boundaries) are formed by varying the treatment procedures (deformation temperature and speed at drawing, annealing temperature). The tensile and impact toughness tests were performed on samples with a V-shaped notch and different structures of commercially pure Ti Grade 4 in the coarse-grained and UFG states. The results demonstrated that grain refinement, higher dislocation density, and their elongated shape were obtained as a result of drawing at 200 С, which led to a decrease in both the uniform elongation at tension and the impact toughness of Ti Grade 4. Short-term annealing at 400-450 C could improve the impact toughness of UFG Ti with a non-significant decrease in strength. This short-term annealing contributes to the dislocation density decrease without considerable grain growth as a result of the recovery and redistribution of dislocations. The dependence of impact toughness on the strain hardening ability of UFG Ti was discussed.

Thermal Stability and Recrystallization of Titanium Grade 4 with Ultrafine-Grained Structure

“…In the range of 450-500°C (0.37-0.39 Tm) the material softened noticeably. This effect has also been found previously during annealing of severely-deformed titanium and has been usually attributed to recrystallization [4,8,9,10]. A further increase in annealing temperature to 600°C (0.44 Tm) resulted in a gradual softening followed by a slight strength increase at higher temperatures.…”

“…Moreover, a remarkable hardening effect is sometimes observed in this temperature range [3][4][5][6]. On the other hand, a further increase of the annealing temperature to 400oC usually leads to material softening and essential restoration of ductility [4,[7][8][9][10], thus evidencing a recovery process [10]. Recrystallization of SPD CP Ti is often found to occur within the temperature interval of 400-500°C [4,[8][9][10].…”

“…On the other hand, a further increase of the annealing temperature to 400oC usually leads to material softening and essential restoration of ductility [4,[7][8][9][10], thus evidencing a recovery process [10]. Recrystallization of SPD CP Ti is often found to occur within the temperature interval of 400-500°C [4,[8][9][10]. This process has been reported to develop via a discontinuous mechanism [4], i.e., it involves nucleation and subsequent growth of recrystallization nuclei.…”

Ultrafine‐Grained Titanium‐Based Alloys: Structure and Service Properties for Engineering Applications

“…Dependence of the impact strength K CV on the uniform elongation δ u of UFG Grade 4 Ti samples. Reproduced with permission . 2018, John Wiley and Sons.…”

The Relationship between Strength and Toughness in Tempered Steel: Trade‐Off or Invariable?

“…Since the plane strain fracture toughness ( K IC ) and impact toughness (CVN) are both used to express material toughness, it appears paradoxical about the variation of them. Several investigations demonstrated that the grain size, second phase, and grain boundary have different effects on the impact toughness and fracture toughness. Ritchie et al emphasized that the contradictory result of the toughness appear to be an indeed indication of important difference between fracture induced by the critical cleavage stress and characteristic distance.…”