Influence of niobium on the thermal and microstructural behavior of TiNiCu shape-memory alloys

Resumo

© 2025 The Authors.NiTi-based Shape Memory Alloys (SMAs), such as Nitinol, are widely used in biomedical applications due to their shape memory effect, superelasticity, and biocompatibility. While copper addition enhances mechanical strength and compositional tolerance, it introduces brittleness, limiting processability. To mitigate this limitation, niobium additions can be used to improve ductility but may increase the hysteresis of the thermoelastic martensitic transformation. The present work analyzes the effect of Nbx (x = 0, 10, 15 at%) in addition to the thermal hysteresis and the microstructure of a Ti50Ni30Cu20 alloy. The results showed that Ti50Ni30Cu20 (reference alloy) is constituted by a martensitic B19 matrix and Ti2(Ni,Cu) particles. Further Nb addition leads to a hypoeutectic microstructure consisting of B2 austenitic matrix and a ductile enriched niobium phase (β-Nb); the interdendritic lamellae was refined with 10 at% Nb, but 15 % resulted in a hyperfine morphology. It also resulted in a lower fraction of intermetallic Ti2(Ni,Cu). In the three alloys studied, only the B2↔B19 transformation was present upon heating and cooling. A reduction in all phase transformation temperatures and thermal hysteresis was also observed. Vickers microhardness decreased with the addition of 10 at% Nb, but it increased again with the introduction of 15 at% of this element, due to the microstructure refinement. The reduction of the Ti2(Ni,Cu) fraction, the suppression of the B19↔B19’ transformation, and the ultrafine hypoeutectic microstructure show that the addition of Nb to NiTiCu alloys has the potential to increase the processability of these materials and promote a new range of applications.

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