Structure and mechanical properties of as-cast Ti-5Sn-xCr alloys

In this study, the effects of chromium (Cr) on the structure and mechanical properties of a Ti-5Sn-based system were examined, with an emphasis on improving the strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti-5Sn and a series of Ti-5Sn-xCr (x=1, 3, 5, 7, 9, 11 and 13 wt%) alloys prepared by using a commercial arc-melting vacuum-pressure casting system were investigated. X-ray diffraction (XRD) for phase analysis was conducted using a diffractometer. Three-point bending tests were performed on all specimens to evaluate their mechanical properties. The experimental results indicate that the structure and mechanical properties of these alloys changed with the addition of various amounts of Cr. The as-cast Ti-5Sn has a hexagonal α׳ phase. When 1 wt% Cr was introduced into the Ti-5Sn alloy, the structure essentially stayed the same. When the Cr content was at 3 wt%, retention of the metastable β phase began. When the Cr content was increased to 5 wt% or greater, the β phase was entirely retained. The ω phase was detected in Ti-5Sn-3Cr and Ti-5Sn-5Cr. Ti-5Sn-5Cr, which had the largest quantity of the ω phase, exhibited the highest microhardness value due to the hardening effect of the ω phase. Among all Ti-5Sn-based alloys, the β-phase Ti-5Sn-7Cr alloy had the lowest elastic modulus. It also exhibited higher bending strength/modulus ratios, which at 26.8 were higher than that of c.p. Ti (8.5) and that of Ti-6Al-4V (17.4). Furthermore, the elastically recoverable angle of this alloy (31.0°) was much greater than that of c.p. Ti (2.7°). In the search for better implant materials, the low modulus, ductile property, excellent elastic recovery capability and high strength/modulus ratio of β-phase Ti-5Sn-7Cr make this alloy a promising candidate.