Mechanics of superelasticity in Ti-30Nb-(8-10)Ta-5Zr alloy

The superelastic behaviour of Ti-30Nb-10Ta-5Zr and Ti-30Nb-8Ta-5Zr (wt.%) biomedical alloys was investigated by tensile testing and in situ synchrotron X-ray diffraction. The phenomenological theory of martensite crystallography and texture prediction based on the Schmid law indicate that alpha '' in Ti-30Nb-10Ta-5Zr forms in untwinned variants. Measurement of single-crystal elastic constants using an Eshelby-Kroener-Kneer self-consistent model shows that the 10-Ta alloy has a C' modulus 3 GPa higher than that of the 8-Ta alloy. That it nevertheless has a proof stress 35 MPa lower can be qualitatively explained by the differences in martensite crystallography. The results suggest that high tensile strength can be maintained for low modulus beta-Ti in spite of martensitic transformation by optimizing transformation strains. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.