Design and characterization of new Ti-Nb-Hf alloys

NiTi alloys are the only shape memory alloys that have been used in biomedical applications. However, in recent studies, it has been demonstrated that the release of Ni ions produces adverse reactions in the surrounding tissue which can generate different kinds of allergy. The objective of this work is to design, produce and characterize new Ni-free Ti alloys as possible substitutes of the NiTi materials and also, enhance bone regeneration by presenting a similar bone elastic response.

 For that, a method based on the molecular orbital theory has been implemented to design three new Ti-Nb-Hf system alloys. A vacuum arc melted button of each alloy was heat treated at 1100 ºC during 2 hours and quenched with a mixture of ethanol/water at 0 ºC. Finally, the alloys were microstructurally and mechanically characterized elastic modulus was obtained as well as the thermoelastic behaviour, which were evaluated by means of nanoindentation tests using a Berkovich and a spherical tip, respectively.

 X-Ray diffraction results show the presence of β phase in the three studied alloys. Moreover, one of the alloys exhibits reversible phase transformation due to the presence of thermoelastic martensitic α” plates inside the β grains observed by transmission electron microscopy. Results show a low elastic modulus in all the studied alloys with values between 70-90 GPa, which are values lower than those of the commercial alloys used in bone implants load transfer.

 

 Keywords: Ni-free Ti alloys, shape memory effect, low elastic modulus, nanoindentation.