This paper studies nanostructured commercially pure Ti (CP Ti) used in producing miniature implants for osteosynthesis in the cranio-facial and mandibular areas. Ti Grade 4 rods are nanostructured by equal-channel angular pressing via the Conform scheme (ECAP-C) and subsequent drawing. Plate-shaped items are designed and produced from nano-Ti. The cross-section of items is reduced, but their static and fatigue strength values are retained. Geometrical aspect and surface treatment of implants produced from nanostructured Ti materials are discussed.

This research is focused on a study of the relationship between mechanical behavior, microstructure and fracture toughness of a Ti-6Al-4V alloy in both coarse-grained (CG) and ultrafine-grained (UFG) conditions. The UFG state with a primary alpha-phase grain size, but with different orientations with respect to the testing direction, was produced by equal-channel angular pressing (ECAP) after thermo-mechanical treatment. Fracture toughness and mechanical testing were conducted at a temperature of 196 °C. A duplex UFG structure formation in the Ti-6Al-4V alloy led to an enhancement of yield stress and a decrease in the fracture toughness at 196 С by comparison with the CG alloy. The lowest values of fracture toughness were observed in a sample in which there were elongated grains lying parallel to the loading direction during testing compared to the situation where the grains were perpendicular to this direction. The reasons for the reduction in fracture toughness in the UFG Ti alloy are discussed.

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The work is aimed at establishing a relationship between the criteria for estimating the local stress state h max / t (where h max is the maximum depth of the plastic zone under the fracture surface, t is the thickness of the sample or part) and the criterion of fracture mechanics t / (K 1C / σ 0.2 ) 2 for materials with an hcp lattice. The titanium alloys Ti-6Al-4Mo and Ti-6Al-4V were investigated in the initial coarse-grained (CG) and ultrafine-grained (UFG) states. The UFG state was processed by rotary forging (RF) in Ti-6Al-4Mo alloy and by equal-channel angular pressing (ECAP) and ECAP followed by isothermal forging (IF) in Ti-6Al-4V alloy. Testing of alloys for static crack resistance (K 1C ) was carried out on prismatic specimens with a thickness of 10 mm according to the three-point bending scheme in a liquid nitrogen environment (−196°C). The depth of the plastic deformation zones under the fracture surfaces was determined by the X-ray method. The test results showed that UFG alloys had a lower K 1C value than the alloys in the CG state. According to the criterion t / (K 1C / σ 0.2 ) 2 > 2.5, the fracture of all samples occurred under plane strain (PS) condition. According to the criterion h max / t <10 −2 , only samples with the UFG structure were fractured under PS conditions. Analysis of the graphical dependence, reflecting the relationship of the criteria t / (K 1C / σ 0.2 ) 2 and h max / t for titanium alloys Ti-6Al-4Mo and Ti-6Al-4V showed that for materials with an hcp lattice, the PS condition can be written as t / (K 1С / σ 0.2 ) 2 ≥10.