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

As-cast Ti–5Nb and a series of Ti–5Nb–xCr with Cr content ranging from 1 to 13 mass% prepared by using a commercial arc-melting vacuum-pressure casting system were investigated. Commercially pure titanium (c.p. Ti) was used as a control. X-ray diffraction (XRD) for phase analysis was conducted with a diffractometer. Three-point bending tests were performed to evaluate the mechanical properties of all specimens. The fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that these alloys obviously had different structures and mechanical properties with the addition of various amounts of Cr. When 1 mass% Cr was added, the structure was comprised mainly of the α′ phase, which was also found in Ti–5Nb. With the addition of 3 mass% Cr, α′ and α′′ phases were appeared. When the Cr content was increased to 5 mass% or greater, the β phase was completely retained. Moreover, the ω phase was detected in the Ti–5Nb–5Cr and Ti–5Nb–7Cr alloys. The largest quantity of ω phase and the highest bending modulus were found in the Ti–5Nb–5Cr alloy, while the Ti–5Nb–9Cr alloy had the lowest bending modulus. Moreover, the high strength/modulus ratios of the Ti–5Nb–3Cr (22.5) and Ti–5Nb–9Cr (21.3) alloys demonstrate its advantage for use as implant materials. Also, these two alloys exhibited the better elastic recovery angles of 28.3° in Ti–5Nb–3Cr and 22.2° in Ti–5Nb–9Cr. In the current search for better implant materials, α′ + α′′ phase Ti–5Nb–3Cr and β phase Ti–5Nb–9Cr alloys with low modulus, ductile property, excellent elastic recovery capability and reasonably high-strength seem to be the most feasible alloy for orthopedic and dental applications if some other necessary properties are obtained.