Investigation of martensitic transformations in Ti-Nb-Zr-O alloys: experiments and alloy design

There is an increasing quest for improved structural biomedical materials. Ti-Nb based alloys are popular due their excellent biocompatibility coupled with low elastic modulus, eventually approaching the one of human bones. The most intriguing properties and phenomena in these materials are associated with martensitic transformations. For instance, martensite formed e.g. by quenching is very compliant while retaining reasonable strength. Moreover, depending on the chemical composition, martensite can be strain-induced and lead to superelastic behavior, which is considered a further option to enhance compliance. In the present contribution, we report on martensitic transformations in Ti-xNb-13Zr-yO alloys, including commercial grade Ti-13-13, by applying dilatometry, X-Ray diffraction, scanning electron microscopy and hardness measurements. The activity is part of an ongoing project on Ti-Nb based alloys. The applied methods provide information on the transformation temperatures, transformation strain and an estimate of the strength of the material as a function of the chemical composition and heat treatment. Selected results of particular interest to the heat treatment community are presented, and it is illustrated how the data can be framed to improve the predictions of a thermodynamics-based tool for the development of new Ti-Nb-Zr-O alloys with improved mechanical properties, ultimately aiming for a higher strength/stiffness ratio.