Microstructures and Stability Origins of β-(Ti,Zr)-(Mo,Sn)-Nb Alloys with Low Young’s Modulus

The present work investigates the microstructural evolution and β-phase stability of a multi-component [(Mo,Sn)-(Ti,Zr)₁₄]-Nb alloy series developed using the cluster-plus-glue-atom model. Low Young’s modulus (E) can be reached, when both low-E elements, Sn and Zr, and β-Ti stabilizers, Mo and Nb, are properly incorporated in the so-called cluster formulas. After the X-ray diffraction and transmission electron microscopy analysis, and in combination with the β-Ti stability measured by the Mo equivalent, the Young’s modulus of β-Ti alloys is found to increase with increasing β stabilities and is closely related to both the microstructures of the β matrix and the precipitated phases. More importantly, the morphologies of the β matrix change with β stabilities apparently so that high-E (E >70 GPa) and low-E (E ≤70 GPa) β-Ti alloys can be distinguished with the microstructures of the β matrix. The quinary alloy, formulated as [(Mo_0.5Sn_0.5)-(Ti₁₃Zr₁)]Nb₁, owns its lowest E of 48 GPa among the present alloy series to the mixed thin-lamellar and rod-shaped morphology of the β structure with the lowest stability for the β formation.