Cryogenic temperature deformation behavior and shape memory mechanism of NiTiFe alloy

The excellent shape memory properties of NiTiFe alloys make them a popular choice for tube connection components and actuators in the aerospace industry. However, in order to obtain these properties, the alloy must undergo pre-deformation at specific cryogenic temperatures to induce the martensitic phase transformation. Despite their widespread use, the deformation behavior and shape memory mechanism of NiTiFe alloys at cryogenic temperatures remain unclear. To address this, we conducted a study investigating the deformation behavior and shape memory mechanism of Ni₄₇Ti₅₀Fe₃ alloy at temperatures ranging from −190 °C to 150 °C using tensile tests, free recovery tests, and EBSD analysis. Our findings suggest that the deformation behavior of NiTiFe alloy can be classified into four classes corresponding to different deformation mechanisms. At temperatures above the M_d (−15 to −30 °C), dislocation slip and {114}_B2 deformation twinning occur without reversible strain. However, reversible and irreversible strains occur simultaneously at temperatures between −50 to −90 °C. At temperatures ranging from −110 to −150 °C, the reorientation/detwinning of the R-phase, stress-induced martensitic phase transformation, and yield stage of martensite occur in sequence. When the deformation temperature is within the range of −165–190 °C, the reorientation/detwinning of martensite occurs during the stress platform stage, and irreversible strain occurs during the yield stage of martensite. The best shape memory effect of the NiTiFe alloy is observed at deformation temperatures near M_f (−180 °C). Moreover, the reverse phase transformation temperatures increase with the increasing deformation amounts, even without plastic deformation. The temperature-dependent deformation map of NiTiFe alloy was obtained based on the tests conducted in this study, from which the influence of deformation temperatures on the different critical stresses and the deformation mechanism under different temperature conditions can be determined.