Abstract
Beta-type titanium alloys contain high-cost alloy elements, and thus the manufacturing process using them is too expensive. In order to solve these problems, with making a good balance of mechanical properties in the titanium alloy, we added low-cost elements (Fe and Mo) rather than the high-cost beta-stabilizing elements (Nb and Zr). Furthermore, boron was added to the Ti alloy because that containing boron, exhibited greater stiffness and strength, along with good fracture resistance. In order to study phase transformation about these alloys, solution treatment and aging were conducted. The knowledge on the solution treatment of the Ti alloy is important for controlling the microstructure, being the key to enhancing the mechanical properties and nucleation sites. The result shows that ${\beta}$-solution treatment leads to a stable ${\beta}$-matrix and provides the greatest driving force for precipitation. This contributed to good ductility (about 900 MPa of ultimate strength with 25% elongation), in Ti-12.1Mo-1Fe (0A1F). However, Ti-12.1 Mo-1Fe-xB (0A1F-0.05B, 0A1F-0.1B) had more ductility than 0A1F. In the solution-treatmentplus-aging condition, the nano-size ${\omega}$ phase that precipitated at $350-450^{\circ}C$ resulted in great strength (above 1500 MPa with 2% elongation). When aged at $550^{\circ}C$, the 0A1F only precipitated ${\alpha}$-phase, and had ductility of about 1100 MPa with 13% elongation. The specimens to which boron was added, had ${\alpha}$ and ${\omega}$ phases; so 0A1F-xB was more brittle than 0A1F when aged at $550^{\circ}C$. Consequently, the design-alloy exhibited good mechanical properties (i.e. strength and elongation). More detailed investigation is needed to determine its optimal mechanical properties.
