Phase stability and tensile properties of metastable β-Ti alloys for orthopedic applications designed using electronic parameters

The design and development of metastable β-Ti alloys with non-toxic elements that are used in the manufacturing of orthopedic implants are gaining significant research attention. In this work, two metastable β-Ti alloys, binary alloy of Ti-17Mo wt% (referred as Alloy A) and ternary alloy of Ti-16.5Mo-1.1Fe wt% alloy (referred as Alloy B) were designed with different values of electronic parameters such as the Molybdenum equivalence (Moeq), electron to atom ratio (e/a), and the Bo-Md. The contribution of the electronic parameters in influencing the formation of phases and the elastic modulus is discussed. Phase characterization and tensile properties of the alloys after solution treatment at 1100 °C and quenched in ice-brine were carried out using different techniques. The X-ray diffraction (XRD) patterns and optical microscopy (OM) micrographs showed that with increasing e/a ratio the β phase stability increases. EBSD phase maps showed the decrease in the volume fractions of α″and ω phases upon addition of Fe. With increase in stability of β phase, the ultimate tensile strength (UTS) and elastic modulus decreased from 912 MPa to 540 MPa and 82 GPa to 73 GPa in Alloy A and Alloy B, respectively. On the other hand, the increase in the β phase stability resulted in increased hardness from 366 Hv_0.5 for Alloy A to 428 Hv_0.5 in Alloy B. Using scanning electron microscopy (SEM), a combination of cleavage facets and dimpled structure were observered in both alloys.