Effect of chromium content on structure and mechanical properties of Ti-7.5Mo-xCr alloys

Abstract

The present work is a study of a series of Ti-7.5Mo-xCr alloys with the focus on the effect of chromium content on the structure and mechanical properties of the alloys. Experimental results show that low hardness, strength and modulus binary Ti-7.5Mo alloy is comprised primarily of fine, acicular martensitic α′ phase. When 1 wt % Cr is added, a small amount of β phase is retained. With 2 wt % or more chromium added, the entire alloy becomes equi-axed β phase with bcc crystal structure. The average β grain size decreases with Cr content. When the alloy contains about 2–4 wt % Cr, a metastable ω phase is present. In Ti-7.5Mo-2Cr alloy appears the highest ω intensity accompanied with high microhardness, bending strength and modulus. The ω-induced embrittling effect is most profound in Ti-7.5Mo-2Cr alloy that exhibits a terrace type fracture surface covered with numerous micron-sized dimples. The alloys with higher Cr contents show normal ductile type fractography with much larger deformation dimples. The present results indicate that Ti-7.5Mo-(4–6)Cr alloys seem to be potential candidates for implant application.