Continuous Production of Pure Titanium with Ultrafine to Nanocrystalline Microstructure

Microstructure of the Advanced Titanium Alloy VT8M-1 Subjected to Rotary Swaging

In this study, the microstructural behavior of the advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn-0.15Si (VT8M-1) alloy during rotary swaging (RS) was investigated. VT8M-1 has increased heat resistance and is considered a replacement for the Ti-6Al-4V alloy. It was shown that, during RS, the evolution of the primary a phase is characterized by the formation of predominantly low-angle boundaries according to the mechanism of continuous dynamic recrystallization. The density of low-angle boundaries increases three times: from 0.38 µm-1 to 1.21 µm-1 after RS. The process of spheroidization of the lamellar (a + b) component is incomplete. The average size of globular a and b particles was 0.3 μm (TEM). It is shown that the microstructures after RS (ε = 1.56) and equal-channel angular pressing (ECAP) (ε = 1.4) are significantly different. The temperature-velocity regime and the predominance of shear deformations during ECAP contributed to a noticeable refinement of the primary a-phase and a more complete development of globularization of the lamellar (a+b) component. EBSD studies have shown that RS leads to the formation of a structure with a higher density of low- and high-angle boundaries compared to the structure after ECAP. The results are useful for predicting alloy microstructure in the production of long rods that are further used in forging operations.

Fatigue properties of UFG Ti grade 2 dental implant vs. conventionally tested smooth specimens

Complicated geometry in combination with surface treatment strongly deteriorates fatigue resistance of metallic dental implants. Mechanical properties of pure Ti grade 2, usually used for dental implant production, were shown to be significantly improved due to intensive grain refinement via Conform SPD. The increase of the tensile strength properties was accompanied by a significant increase in the fatigue resistance and fatigue endurance limit. However, the SLA treatment usually used for the implants' surface roughening, resulted in the fatigue properties and endurance limit decrease, while this effect was more pronounced for the ultrafine-grained comparing to the coarse-grained material when tested under tensile-tensile loading mode. The testing of the implants is usually provided under the bending mode. Even though different testing condition for the conventional specimens tests and implants testing was adopted, a numerical study revealed their comparable fatigue properties. The fatigue limit determined for the implants was 105% higher than the one for coarse-grained and only by 4 % lower than the one for ultrafine-grained Ti grade 2. Based on the obtained results, conventional specimens testing can be used for the prediction of the fatigue limit of the implants.

Optimization of the Mechanical Performance of Titanium for Biomedical Applications by Advanced, High-Gain SPD Technology

This recent study deals with the optimization of the mechanical performance of Grade 2 and Grade 4 titanium with Conform severe plastic deformation (SPD) processing and subsequent rotary swaging. A comprehensive study of the materials behaviour and characterisation during and after processing is given by (finite element method - FEM) numerical simulation, microscopy methods and mechanical testing. The mechanical and fatigue properties are discussed in terms of texture and microstructure evolution. It is shown that the combination of Conform SPD and rotary swaging is a promising technique for economically reliable, high-gain production of titanium alloys fulfilling requirements for biomedical applications. Such a processing can improve the mechanical properties of the unalloyed titanium to the level of the commonly used Ti-6Al-4V.