Mechanical properties of UFG titanium: Notched fatigue and impact toughness

• Published in: Materials letters Vol. 302; p. 130366
• Main Authors: Polyakov, Alexander V., Raab, Georgy I., Semenova, Irina P., Valiev, Ruslan Z.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2021; Elsevier BV
• Subjects: Annealing; CP titanium; Equal channel angular pressing; Etching; Fatigue properties; Fatigue strength; Fatigue tests; Heat treating; Impact strength; Impact toughness; Materials science; Mechanical properties; Notch; Surgical implants; Titanium; Toughness; Ultra-fine grained; Ultrafines; Ultra-fine grained; Impact toughness; Fatigue properties; CP titanium; Notch
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/j.matlet.2021.130366

•Ultrafine-grained structure in metals reduces their toughness.•The increased toughness of UFG titanium grade 4 is an important parameter for threaded products such as medical implants.•Short-term high temperature annealing increases the Charpy impact energy of the ultrafine-grained (UFG) titanium grade 4.•Etching finish of a stress raisers increases the fatigue resistance of notched specimens of UFG titanium grade 4. This paper focuses on the study of the impact toughness and fatigue strength with a notch of ultrafine-grained titanium Grade 4 for advanced medical implants. An ultrafine-grained structure was formed in titanium by equal-channel angular pressing according to the “Conform” scheme followed by short-term annealing. The criterion for choosing the annealing regime was the achievement of a combination of increased impact toughness and preserving of enhanced strength due to the formation of a bimodal UFG structure. Impact toughness was assessed on standard specimens with a V-notch. Fatigue tests were carried out on specimens with a stress concentrator simulating a thread in a medical device. The positive effect of finishing etching with a mixture of nitric and hydrofluoric acids, which is widely used in dental surgery for medical implants, has been revealed. It is shown that a change in the surface topography of the notch, characterized by of surface microdefects after etching, leads to an increase in the fatigue strength σ-1 by about 15% (from 180 to 220 MPa).