Effects of chromium addition on structure and mechanical properties of Ti–5Mo alloy

• When Cr content was increased to 3 mass% or greater, the β phase was retained.
• The ω phase was detected only in Ti–5Mo–(3, 4, and 5)Cr.
• The low-modulus Ti–5Mo–1Cr exhibited the highest strength/modulus ratio.

Titanium and its alloys have been widely used as biometals due to their excellent biocompatibility, corrosion resistance and moderate mechanical properties. As-cast Ti–5Mo and a series of Ti–5Mo–xCr (x = 1, 2, 3, 4, 5, 7 and 9 mass%) alloys were designed and fabricated for the first time to develop novel biomedical materials. Commercially pure titanium (c.p. Ti) was used as a control. The experimental results indicated that the structure and mechanical properties of these alloys changed as different amounts of Cr were added. The Ti–5Mo alloy was composed mainly of α′ phase. When 1 mass% Cr was added, the structure was changed to α″ phase. The addition of 3 mass% or greater Cr content resulted in β-phase Ti–5Mo–xCr alloys. ω phase formed in alloys containing 3–5 mass% Cr. The largest quantity of ω phase and highest bending modulus were found in Ti–5Mo–3Cr. With the exception of ω-phase Ti–5Mo–3Cr and Ti–5Mo–4Cr, the Ti–5Mo–xCr and Ti–5Mo alloys had good bending ductility. α″-phase Ti–5Mo–1Cr had the highest bending strength/modulus ratio (23.4). This ratio is higher than that of c.p. Ti (8.5) by 175% and the Ti–5Mo alloys (20.3) by 15%. The elastic recovery angle of the Ti–5Mo–1Cr (28.4°) was about 10.5 times greater than for c.p. Ti (2.7°). In the search for a better implant material, α″-phase Ti–5Mo–1Cr, with its low modulus, ductile property, excellent elastic recovery capability, and reasonably high strength, is a promising candidate.