β-Ti Alloys with Low Young’s Moduli Interpreted by Cluster-Plus-Glue-Atom Model

β-Ti bio-alloys with low Young’s moduli (E) require multiple alloying using both BCC stabilizers and low-E elements. In this study, the cluster-plus-glue-atom model was introduced in the composition interpretation and design of Ti-based (Ti,Zr)-(Mo,Sn)-Nb alloys. Alloying elements are grouped according to their enthalpies of mixing with Ti, forming a general cluster formula [(Mo,Sn)(Ti,Zr)14]Nb1 or 3, where the square brackets enclose the nearest neighbor coordination polyhedron cluster CN14 of the BCC structure and Nb is the glue atom. The formulated compositions could reach simultaneously low E and high β-Ti structural stabilities, as exemplified by [(Mo0.5Sn0.5)(Ti13Zr)]Nb1 which had a Young’s modulus as low as 48 GPa in the suction-cast state.