Microstructure evolution and functional response of NiTi shape memory alloy manufactured by dual-wire electron beam freeform fabrication

• Published in: Journal of manufacturing processes 2024-06, Vol.119, p.842-855
• Main Authors: Song, Debin, Wang, Ting, Wei, Lianfeng, Jiang, Siyuan
• Format: Article
• Language: English
• Subjects: Dual-wire EBF3; NiTi shape memory alloy; Phase transformation; Shape memory effect; Superelasticity
• ISSN: 1526-6125
• DOI: 10.1016/j.jmapro.2024.03.089

In this work, the thin-walled NiTi alloy was fabricated by dual-wire electron beam freeform fabrication (EBF3) technology. The effects of process parameters on the composition uniformity, martensitic transformation behavior, mechanical and functional properties of the NiTi alloy were further investigated. The results showed that improper beam current, feeding speed and travel speed caused the uneven distribution of Ni and Ti elements in the as-built samples, which led to a large amount of Ti2Ni precipitations in the NiTi depositions. And no obvious martensitic phase transition temperature can be detected in the range of −70– 130 °C. The increase of heat input was beneficial for promoting element mixing. The NiTi alloy with uniform composition was composed of coarse columnar B2 austenite and a small amount of sub-micron Ti2Ni phase at room temperature. During heating and cooling process, it exhibited a single reversible martensitic transformation (B2↔B19′). The increase of Ni volatilization with the increase of heat input led to an increase of phase transition temperature. The samples showed satisfactory compressive mechanical properties. The compressive strength and elongation of deposited NiTi alloys were higher than 3.1 GPa and 37 %, respectively. The shape memory recovery rate and superelastic recovery rate of the optimized NiTi alloy were 89.87 % and 83.39 %, respectively. The results provided a valuable reference for low-cost and flexible manufacturing of NiTi alloy structural parts with complex shapes. [Display omitted] •NiTi alloys were deposited using dual-wire electron beam freeform fabrication.•Controlling the travel speed was crucial for obtaining the homogenized composition.•NiTi alloy parts had good superelasticity and excellent shape memory effect.•The homogenization mechanism of Ni and Ti elements was discussed.