Titanium has many limitations in coverage and frequency of application due to its expensive alloying elements and complex manufacturing process. The biocompatible Ti-Mo-Fe ternary beta titanium alloys were designed by replacing high-cost beta-stabilizer elements (V, Nb, Zr, etc.) with low-cost Mo and Fe elements. In addition, it was attempted to obtain a low-cost, high-strength beta-titanium alloy with 800 MPa or more by applying the powder metallurgy process technology to the Ti-Mo-Fe alloy system. The added Mo element has the effect of reducing the elastic modulus of the titanium alloy without reducing its strength. In this study, Ti-Mo-Fe alloys designed with different Mo contents were fabricated using a powder metallurgy process and analyzed in connection with microstructural properties, phase changes, and mechanical properties. As Mo contents are increased, the α-lath thickness of Widmanstätten decreases and the size of prior β grain decreases. It was confirmed that the hardness and tensile strength were excellent and were compared with the ingot material of the same alloy system.

Titanium and titanium alloys are promising implant metallic materials because of their high strengths, low elastic moduli, high corrosion resistances, and excellent biocompatibilities. A large difference in elastic modulus between the implant material and bone leads to a stress shielding effect, which increases the probability of implant separation or decrease in the bone density around it. Thus, a lower elastic modulus is required for a better implant metallic material. β titanium has a lower elastic modulus and high strength and can reduce the probability of the stress shielding effect. In this study, the applicability of the Ti–39Nb–6Zr+0.45Al alloy, obtained by adding a small amount of aluminum to the Ti–39Nb–6Zr alloy, as a biomedical implant material was evaluated. The mechanical properties and biocompatibility of the alloy were evaluated. The biocompatibility of Ti–39Nb–6Zr+0.45Al was similar to that of Ti–39Nb–6Zr according to in vitro and in vivo experiments. In addition, the biological corrosion resistances were evaluated through a corrosion test using a 0.9% NaCl solution, which is equivalent to physiological saline. The corrosion resistance was improved by the addition of Al. The yield strength of the Ti–39Nb–6Zr+0.45Al alloy was improved by approximately 20%. The excellent biocompatibility confirmed its feasibility for use as a biomedical implant material.

Titanium alloys that are used in biomedical applications must possess biocompatibility and a low elastic modulus so that they protect host bone tissue without causing stress shielding. As the elastic modulus of beta Ti alloys is close to that of bone (10–30 GPa), these alloys are considered potential orthopedic implant materials. The elastic modulus of the single β-phase Ti-39Nb-6Zr (TNZ40) alloy is approximately 40 GPa, whereas the strength is lower than that of other types of Ti alloys. Interstitial oxygen in a Ti matrix is well known to improve the matrix strength by solid-solution hardening. The desired mechanical properties can be optimized using a thermo-mechanical procedure to maintain a low elastic modulus. In order to enhance the strength, TNZ40 alloys were fabricated with different amounts of oxygen. The TNZ-0.16O and TNZ-0.26O alloys were cold swaged into 11 mm diameter bars, subjected to solution treatment at 900 °C and 950 °C for 2 h, and furnace-cooled to room temperature. As a result, recrystallized grains were clearly observed in the β matrix. The TNZ-0.26O alloy that was cold-worked by swaging followed by solution treatment at 900 °C exhibited the best mechanical properties (Vickers hardness: 247 HV, ultimate tensile strength: 777 MPa, elongation at rupture: 18.6%, and compressive strength: 1187 MPa). This study reports the effects of oxygen content on the recrystallization behavior and mechanical properties of these alloys.

Ti-2.5Zr-5.0Hf-37.5Cu-7.5Ni-1.0Si-5.0Sn (at.%) BMG has been successfully manufactured in amorphous powder with a size of about 25 μm (D₅₀). Using this amorphous powder, a Ti-based BMG was manufactured by an additive manufacturing process based on a laser powder bed fusion (LPBF) technique. In 3D printing processes using amorphous powders, it is necessary and important to understand the crystallization behavior due to the difference in energy density applied to the powders. An LPBF process has been carried out with various energy density conditions to minimize the inner defects and identify the sound mechanical properties of 3D-printed BMG parts. At the lowest energy density condition (3.0 J/mm³), the most pores were generated. Even if the same energy density (3.0 J/mm³) was applied, the rapid laser movement caused many pores to form inside the material. The relatively sound 3D-printed Ti-based BMG was successfully fabricated with a size of about 5 mm × 5 mm × 3 mm. Peaks at 41° and 44° showing crystallization were observed in all conditions. The higher the laser power was, the greater each peak intensity and the more crystallization (CuTi, Ti₃Cu₄, etc.) was present in the BMG, and the higher the scan speed, the more the internal defects were found.

The dissimilar welding of titanium and copper by fusion welding is very difficult because the melting points of the materials are very highly different and strong brittle intermetallic compounds (IMCs) can be easily produced in welded zone and heat-affected zone, etc. Friction stir welding was employed as a type of solid-state welding for Ti/Cu dissimilar welding to obtain a sound welded zone and reduce the total process cost. This study investigated how the metal flow of the welded zone changes according to the variation in the rotational speed of the tool, from 450 rpm to 600 rpm. When the rotational speed was too high, the plastic flow of the softened material increased and intermetallic compounds such as TiCu, Ti2Cu3, and Ti2Cu, were generated in the Cu region of the welded zone. The microstructural evolution of AS (Advancing Side) and RS (Retreating Side) were investigated and the soundness of the welded zone and its mechanical properties were evaluated through the microstructural evolution. A high hardness value of 200 Hv or more was exhibited in some points, due to the formation of intermetallic compounds in the RS (Cu) region. Ti/Cu dissimilar friction stir welding at a welding speed of 50 mm/min and an appropriate rotation speed of 500 rpm showed a good welded zone and mechanical properties.

Beta-type titanium alloys have a low elastic modulus, excellent cold workability, and are widely used as implant materials. High strength is possible by forming a precipitation in the β-matrix via solution treatment and aging treatment. However, beta titanium alloys require a large amount of beta-stabilizing elements (Fe, Nb, Mo, Ta, etc), and these expensive beta stabilizing elements increase the manufacturing cost of these alloys. In this study, Ti-5Mo-2Fe metastable beta-titanium alloy was designed by adding Mo and Fe, which were relatively inexpensive and had excellent biocompatibility among beta-stabilizing elements, and an ingot was manufactured by vacuum arc remelting. Solution treatment was maintained at 850oC for a holding time of 1 hour, followed by furnace cooling. Aging treatments were conducted in a range of temperature 350~500oC and holding time 2 h~48 h. The microstructure behaviors and mechanical properties were analyzed according to these aging treatment conditions. Isothermal ω phases were precipitated by aging treatment, and hardness and yield strength were found to be significantly higher for conditions of 400oC, 8h. As holding time and temperature increased, these phases transformed into secondary alpha phases and the hardness and yield strength decreased due to this microstructural evolution.