PSI - Issue 69

Carlo Alberto Biffi et al. / Procedia Structural Integrity 69 (2025) 121 – 126

126

Table 3: Transformation temperatures and heat exchanged upon cooling, at varying the laser power P [W] Rs [°C] Rf [°C] Ms [°C] Mf [°C] h [J/g] 45 49 35 -24 -59 12 55 44 30 -2 -23 21 65 39 33 22 1 26 75 - - 36 13 26 85 - - 38 32 25 4. Conclusions The present work explored the effect of the principal process parameters, such as laser power and scanning speed, on the transformation temperatures in thin Ti rich-NiTi wires, subjected to laser shape setting. The cold worked wires, subjected to a suppressed martensitic transformation due to the induced plastic deformation, was successfully treated by laser scan for inducing the martensitic transformation. The optimal range of laser process parameters, able to induce a promising martensitic transformation, was explored from a large feasibility window, defined by the scanning speed value (interval in the range 45-55 mm/s) and laser power (interval in the range 45-95 W). In general terms, at low power values, the transformation was composed from two distinct peaks upon cooling, while at high power a single peak transformation was induced. More specifically, at 45 mm/s, the most suitable laser power for promoting promising functional performances was selected at 55 W, while the increase of the scanning speed up to 50-55 mm/s, shifted forward higher laser power up to 65 W. These laser conditions promoted a martensitic transformation largely comparable with the industrial reference for promoting SME performances usable in SMA based actuators. [1] Otsuka K. and Wayman C. M., Shape Memory Materials (Cambridge University Press, USA, 1998). [2] Yiong L., Youn L., Van Humbeek J., Two-way shape memory effect developed by martensite deformation in NiTi, Acta materialia 47-1 (1999) 199-209. [3] Tuissi A., Bassani P., Mangioni A., Toia L., Buttera F., SMST 2004 Proceedings of the International Conference on Shape Memory and Superelastic Technologies, (2005) 501-508. [4] Huang X., Liu Y., Effect of annealing on the transformation behavior and superelasticity of NiTi shape memory alloy, Scripta Materialia, 45 (2001) 153-160. [5] Miller D.A., Lagoudas D.C., Influence of cold work and heat treatment on the shape memory effect and plastic strain development of NiTi, Materials Science and and Engineering A 308 (2001) 161-175. [6] Mitwally M., Farag M., Effect of cold work and annealing on the structure and characteristics of NiTi alloy, Materials Science and and Engineering A 519 (2009) 155-166. [7] Malard B., Pilch J., Sittner P., Gartnerova V., Delville R., Schryvers D., Curfs C., Microstructure and functional property changes in thin Ni–Ti wires heat treated by electric current—high energy X-ray and TEM investigations, Functional Materials Letters, 5-2 (2009) 45–54. [8]Welp E. G., Langbein S., Survey of the in situ configuration of cold-rolled, nickel-rich NiTi sheets to create variable component functions, Materials Science and Engineering A, 481–482 (2008) 602–605. [9] Meng Q., Liu Y0., Yang H., Shariat B.S., Nam T., Functionally graded NiTi strips prepared by laser surface annealing, Acta Materialia 60 (2012) 1658–1668. [10] Meng Q., Liu Y., Yang H., Nam T., Laser annealing of functionally graded NiTi thin plate, Scripta Materialia 65 (2011) 1109-1112. [11] C.A. Biffi, R. Casati, A. Tuissi, Laser shape setting of NiTinol thin wires, Smart Materials and Structures. 2016, 25 01LT02; doi:10.1088/0964-1726/25/1/01LT02. [12] A. Tuissi, M. Coduri, C.A. Biffi, Laser Shape Setting of Superelastic Nitinol Wires: Functional Properties and Microstructure, Functional Materials Letters (2017) DOI: 10.1142/S1793604717400082. Invited. [13] C.A. Biffi, A. Tuissi, Laser shape setting of superelastic NiTi wire: effects of laser beam power and axial pre-load, 2019 Smart Materials and Structures. https://doi.org/10.1088/1361-665X/ab1e86. [14] Carlo Alberto Biffi, Karthik Mathivanan, Ausonio Tuissi, Laser-Induced Superelasticity in NiTinol Stent Strut, Shap. Mem. Superelasticity (2018) 4:377-382. DOI 10.1007/s40830-018-0183-y. References