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

• Published in: Advanced engineering materials Vol. 20; no. 5
• Main Authors: Polyakov, Alexander Vadimovich, Semenova, Irina Petrovna, Bobruk, Elena Vladimirovna, Baek, Seung Mi, Kim, Hyoung Seop, Valiev, Ruslan Zufarovich
• Format: Journal Article
• Language: English
• Published: 01-05-2018
• Subjects: Ductility; ECAP‐Conform; Grain boundaries; Impact toughness; Strength; Titanium; Ultrafine‐grained structure
• ISSN: 1438-1656; 1527-2648
• DOI: 10.1002/adem.201700863

This study aims at achieving the best combination of strength, ductility, and impact toughness in ultrafine‐grained (UFG) Ti Grade 4 produced by equal‐channel 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.
This study is focused on possibility of achieving the high impact toughness in UFG Ti rods processed by ECAP‐Conform with subsequent drawing. It is demonstrated that the annealing at 425–450 °C for 30 min can improve the impact toughness from 85 to 130 kJ m–2 of UFG Ti with a non‐significant decrease in tensile strength.