Improving functional behavior of a novel Ti-18Zr-13Nb-2Sn shape memory alloy by thermomechanical treatment

The paper is aimed at developing a thermomechanical treatment route to achieve an optimal combination of mechanical and functional properties in Ti-18Zr-13Nb-2Sn shape memory alloy for orthopedic implantology. The thermomechanical treatment parameters were varied as follows: homogenization annealing (900°C, 60 min; 1000°C, 120 min); cold rolling (e = 0.3; e =1.5); post deformation annealing in the temperature range of 500 – 800°C for 30 min. At the initial stage, the alloy was subjected to hot rolling (e = 0.3, 600°C) and in the final step, the aging at 300°C for 15 min. The optical microscopy, X-Ray diffraction, hardness measurement and mechanical tensile testing were used to estimate the effect of the thermomechanical treatment on the structure, phase composition, mechanical and functional properties of the alloy. In result, the most promising thermomechanical treatment includes hot rolling (e = 0.3, 600°C), homogenization annealing (1000°C, 120 min), cold rolling (e = 0.3), post-deformation (650°C, 30 min) and subsequent aging (300°C, 15 min). This leads to the achievement of following functional properties: dislocation yield stress σdis ≈ 582 MPa, maximum achieved strength σmax ≈ 652 MPa, superelastic recovery strain εrse = 3.0 %, the transformation yield stress σtr ≈143 MPa and an apparent mechanical Young’s modulus E ≈ 38 GPa. Such combination of functional properties includes high strength and the perfect superelastic behavior with low Young’s modulus which is highly beneficial for the biomechanical compatibility and live-time of the alloy.

1. the financial support of the Russian Science Foundation - 25-19-00871