Microstructural Evolution and Mechanical Properties According to Aging Conditions of Ti-5Mo-2Fe Alloy

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.