Fabrication and characterization of novel low-cost ternary titanium alloys

Abstract

Titanium and titanium alloys are commonly used in applications such as aerospace and biomedical due to their excellent mechanical properties as well as biocompatibility. However, reduction of the cost in titanium alloys is still sought after aiming to expand the use of titanium to other consumer industries. By alloying β-stabilizer elements with titanium, superior mechanical properties can be obtained.

Novel ternary α + β Ti-xCu-xNb, Ti-xMn-xNb, Ti-xFe-xNb, Ti-xFe-xCu and Ti-xFe-xMn (x = 0.5, 1, 2, 3.5 and 5 in wt%) alloys were designed aiming to have enhanced mechanical properties compared to unalloyed titanium at lower cost. In this study, the alloys were fabricated via powder metallurgy (i.e. cold press and vacuum sintering) to lower the production costs. The microstructure and phase identification of the sintered alloys were performed using optical microscopy, scanning electron microscopy and X-ray diffraction. Mechanical properties were analysed through tensile testing and the Rockwell hardness test.

Experimental results showed that the mechanical properties (tensile and hardness) of all sintered ternary titanium alloys, proportionally increase with the amount of alloying elements added, nevertheless, ductility decreases.

High tensile properties were observed for the Ti-5Fe-5Cu alloy (due to the formation of the Ti2Cu phase, the strong β-stabilizer effects of Fe as well as a refined microstructure), in comparison to all the sintered ternary titanium alloys. Ti-5Fe-5Mn showed the highest hardness compared to all the sintered ternary titanium alloys, owing to the strong β-stabilizer effects of Fe and Mn (strong solid-solution strengthening effect), and an equiaxed microstructure. Cu and Nb as alloying elements added to Ti show high ductility compared to Fe and Mn, because of that the Ti-xCu-xNb alloy system showed higher elongations than the other alloy systems at the same total amount of alloying elements. It is worth mentioning that Ti-5Fe-5Cu was the only alloy to show comparable UTS and YS with Ti-6Al-4V, and Ti-5Fe-5Mn showed higher hardness compared to Ti-6Al-4V.