Form reminiscence alloys (SMAs) are glorious practical supplies which might be broadly utilized in numerous fields, together with medical, aerospace, automation, and so forth [1], [2]. The form reminiscence impact [3], [4], superelastic habits [5], [6], [7], elastocaloric impact [8], [9] and magnetocaloric impact [10], [11] function the elemental foundation for his or her widespread industrial purposes and stay a key focus of present analysis. Moreover, all of those results are intently related to the first-order martensitic transformation (MT), which is the bodily foundation for the wonderful properties of those alloys. Consequently, comprehending and controlling the MT habits is likely one of the difficult duties to enhance these alloys’ efficiency and design new practical supplies.
Reversible diffusionless MT can happen in form reminiscence alloys below the affect of exterior components equivalent to temperature or stress. Usually, the high-temperature austenitic section reveals a cubic construction with excessive symmetry. In distinction, the low-temperature martensitic section is complicated because of the emergence of quite a few nano-twins and macro-twins that accompany its formation [4], [12]. Totally different purposes necessitate particular section transformation processes and merchandise. For example, the SMAs exhibit superelasticity because of stress-induced MT. When they’re used as a damping materials in gadgets, it’s important for the alloys’ stress-strain curve to exhibit a big hysteresis width and recoverable deformation [13]. Conversely, when larger elastic energy-storage capability and cyclic stability are required below exterior stress cycles, it’s preferable for the alloys to show ultralow hysteretic and even non-hysteretic stress-strain responses [14], [15], [16], [17]. Equally, the reversible magnetic-field-induced pressure (MFIS) impact, generated by twin boundaries shifting below the affect of exterior stress produced by a magnetic area, necessitates a modulated martensitic construction with a decrease driving pressure, because of its decrease twin stress [18], [19], [20]. Then again, a non-modulated (NM) martensitic construction is important for a bigger deformation variable as a result of it has a bigger (1-c/a) worth [21]. It’s evident that the complicated and various MT habits performs a crucial function within the widespread usages of form reminiscence alloys in numerous fields. Due to this fact, controlling the transformation to satisfy totally different software necessities turns into important.
Quite a few efforts have been dedicated to controlling the MT habits of SMAs by numerous strategies. The everyday methods are composition adjustment and factor doping, because the MT habits, together with the martensitic floor state and transformation temperature of this alloy, is very depending on materials composition [22], [23], [24], [25], [26], [27]. Moreover, warmth therapy and mechanical coaching are additionally broadly used to switch the MT traits [28], [29], [30], [31], [32], [33]. Furthermore, some research have demonstrated that precipitate microstructures have profound impacts on the MT course of [34], [35], [36]. These precipitates introduce focus heterogeneity, coherency stress area, and geometrical confinement within the mother or father section, which all have an effect on the MT habits. Introducing defects is one other methodology to tailor the MT. Reviews have revealed that vacancies can fine-tune the transformation temperature [37], [38], whereas a excessive focus of defects can inhibit the MT, resulting in a pressure glass formation [39], [40], [41], [42]. By means of these strategies, the management of MT habits has been achieved, leading to a efficiency enchancment of SMAs. Nonetheless, it’s famous that each one of those investigations have been carried out on the macroscale. Exactly controlling the MT in particular areas on the microscale and nanoscale stays difficult, however is essential for the applying of SMAs in micro-/nano-devices. Significantly with the speedy improvement of micro-electromechanical methods (MEMS) lately, SMAs have emerged as promising candidates for the following technology of MEMS gadgets. As well as, the flexibility to manage the martensitic transformation on the micro-/nano-scale degree can even information macro-control and additional comprehension of SMAs’ transition mechanism. Not too long ago, a number of research have targeted on the microscopic MT habits of the SMAs [43], [44], [45], [46], [47], [48], [49], [50], [51], [52]. However, there’s a lack of reviews addressing the institution of exact management over the MT on the micro-/nano-scale degree.
On this work, the site-specific management of the MT habits was achieved in form reminiscence alloys on the microscale. The basic Ni-Mn-Ga magnetic form reminiscence alloy was chosen because of its complicated martensitic construction and various MT processes, and displacive omega section transformation was induced in defect-free single crystal alloy by high-energy gallium ion beam irradiation. In-situ transmission electron microscopy (TEM) cooling experiments revealed that distinct MT processes occurred within the irradiated and intrinsic areas of the pattern, indicating that the microscale management of MT will be achieved by high-energy ion beam irradiation. Moreover, ab-initio calculations have been carried out to help the experimental outcomes. This work supplies a novel strategy to controlling the MT habits and associated efficiency of form reminiscence alloys on a micro-/nano-scale degree.