Alloy design and property evaluation of new β type titanium alloy with excellent cold workability and biocompatibility

Alloy designing of new β type titanium alloy with excellent cold workability and biocompatibility was conducted by using total heat numbers of 38 titanium alloys containing Nb, Fe, Ta or Zr in basic compositions of Ti-10%Mo-2%Fe and Ti-14%Mo. Cold workability was evaluated based on hardness values obtained by solution treating and after cold rolling with a rolling reduction ratio up to 90% as well as a critical rolling reduction ratio for onset of cracking. Excellent cold workability in β type titanium alloy was obtained by enhanced thermal and mechanical stability of β phase through optimum addition of β stabilizing elements in Ti-14%Mo base alloy and a reduction of β transus below 1000 K. Newly developed alloy of 71-14%Mo-3%Nb-1.5%Zr yields Vickers hardness values of 240 and 284 in as solution treating and after a cold rolling reduction ratio of 90%, respectively, and no cracking occurs in rolling reduction ratio up to 90%. New titanium alloy shows the almost similar level of non-toxicity to other implant titanium materials in the cell culture test using L929 cells, although a slightly increased passive current density is observed by anodic polarization test in both solutions of saline and 1 nnass% lactic acid. New austenitic stainless steel of Fe-6%Mn-22%Cr-10%Ni-2%Mo-0.4%N used as one of comparative materials for evaluation of biocompatibility results in the same level of non-toxicity with new titanium alloy, while relatively poor non-toxicity of the Type 316L steel is observed by cell culture test.