Effect of Nb Addition on Martensitic Transformation Behavior of AuTi-15Co Based Biomedical Shape Memory Alloys

Abstract

The effect of quaternary addition of Nb being from 0 to 2 mol% on the phase constitution, phase transformation behavior and shape memory behavior of Au-50 mol%Ti-15 mol%Co (AuTiCo) alloys is studied. X-ray diffraction analysis shows that, with increasing Nb concentration, the primary phase appeared at room temperature changes from B19 orthorhombic martensite phase to B2 cubic parent phase, and that all the lattice parameters are not largely changed by Nb addition. The maximum transformation strain evaluated in 2 mol%Nb-added AuTiCo is 7.4%. Differential scanning calorimetry revealed that the reverse martensitic transformation finish temperature (A f ) decreases from 414 K in Nb-free AuTiCo to 303 K by 2 mol%Nb addition. The ratio of A f change by Nb addition is evaluated to be ¹55 K/mol%Nb, that is comparably larger than ¹31 K/mol%Nb in NiTi. These results indicate that Nb addition is effective to stabilize B2 parent phase. AuTiCo alloy containing less than 2 mol%Nb exhibits shape memory effect with 90% shape recovery ratio. Besides, AuTiCo containing 2 mol%Nb exhibits 2.8% superelastic shape recovery at room temperature as well as 7.4% maximum transformation strain. Therefore, Nb addition to AuTiCo is effective to decrease the martensitic transformation temperature and to improve superelasticity, although the transformation temperature hysteresis increases by Nb addition, similar to Nb-added NiTi.

Compressive Deformation Behavior and Magnetic Susceptibility of Au₂CuAl Biomedical Shape Memory Alloys

“…It should be noted that the disappearance of forward martensitic transformation in DSC measurements has been sometimes reported in SMAs such as Nb-added AuTiCo. 19) XRD results and DSC results are consistent with each other. Microstructure of 25Cu was reported.…”

Mechanical and Superelastic Properties of Au-51Ti-18Co Biomedical Shape Memory Alloy Heat-Treated at 1173 K to 1373 K

“…Nowadays, Au-Ti-Co ternary alloys have received a lot of attention owing to their good biocompatible and sufficient X-ray radiographic properties [1][2][3][4]. These features fulfill a drawback of Ni-Ti practical alloys which are the possibility of Ni-hypersensitivity [5][6] and not enough X-ray radiography [7][8].…”