Tailoring mechanical and surface properties of UFG CP-Ti by the low-temperature annealing

This work offers the approach to exploit simple and cost-effective low-temperature annealing treatment to simultaneously enhance of hardness, corrosion and biological response of the ultra-fine grained commercially pure titanium (UFG CP-Ti) fabricated by multiple-pass cold rolling technique. Performed investigations revealed that improvement of all of these characteristics was possible by subjecting UFG CP-Ti to the heat treatment with parameters 250 °C/15 min. Hardening (for about 4.2 %) was governed by both partial recovery process of UFG structure and segregation of impurities atoms during annealing. Thereby, this beneficial effect was achieved only in titanium with a certain level of impurities (UFG Ti Grade 2). Enhancement of the corrosion resistance in fluoridated medium (increase of the passive layer resistance Rp from 0.28 ± 0.16 to 3.48 ± 0.18 MOhm*cm 2 ) and osteoblast-like response was closely related to the thermally-induced changes in the passive layer characteristics e.g. growth of its thickness (from c.a. 6 to 11 nm) and changes in the nanotopography (increase arithmetic deviation of surface roughness Ra from 5 ± 1 to 10 ± 2 nm). Overall results indicate that the low-temperature annealing is an effective way to improve both bulk and surface properties of biomedical UFG CP-Ti, which could be easily transferred to the industrial scale.