Optimization of thermal deflection in NiTi-based bimorph microactuators

Bolocan, Vlad; Vâlsan, Dragoș Dumitru; Chilnicean, Gheorghe Amadeus; Novac, Andrei

doi:10.1016/j.matpr.2020.12.122

Cited by 2 publications

(3 citation statements)

References 14 publications

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“…Enhancement of the strength of the matrix is highly required to suppress plastic deformation, thus improving their functional stability. Figure 8 shows the superelastic curves of the homogeneous and geometrically g ed NiTi samples after aging at 250 °C for different durations (1,4,12,24,48, and 120 h). homogeneous samples, aging for 1 h has a negligible effect on the functional stab and the residual strain remains 2.8% after 20 loading-unloading cycles (Figure 8a).…”

Section: Superelasticitymentioning

confidence: 99%

“…Although the as-annealed metrically graded specimens are more prone to introduce plastic deformation (Figur the functional stability could be improved to a level comparable to that of the hom neous specimens after long-term aging treatment (e.g., 120 h). It is suggested that the cumulated residual strains of all the geometrically graded samples were less than 1% ter 20 loading-unloading cycles after aging treatment at 250 °C for 120 h (Figure 8l,r Force (N) Figure 8 shows the superelastic curves of the homogeneous and geometrically graded NiTi samples after aging at 250 • C for different durations (1,4,12,24,48, and 120 h). For homogeneous samples, aging for 1 h has a negligible effect on the functional stability, and the residual strain remains 2.8% after 20 loading-unloading cycles (Figure 8a).…”

Section: Superelasticitymentioning

confidence: 99%

“…NiTi shape memory alloys (SMAs) show unique superelasticity (SE) and shape memory effect (SME), which originate from the reversible thermoelastic martensitic transformation between a B2-structured austenite (A) phase and a B19 -structured martensite (M) phase [1][2][3][4]. These unique properties have attracted widespread interest, including for aerospace [5][6][7], biomedicine [8][9][10], and micro-electromechanical systems [11,12]. During the stress-induced martensite transformation (SIM), a stress plateau occurs over a large strain of 5-7% [13,14].…”

Section: Introductionmentioning

confidence: 99%

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Superelasticity of Geometrically Graded NiTi Shape Memory Alloys

Chen,

Xi,

Jiang

et al. 2023

Metals

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A stress plateau with a strain of 5–8% normally occurs during the stress-induced martensite transformation (SIM) of NiTi shape memory alloys. Within the stress plateau, the correlation between the stress and strain is lost, which limits their application in certain fields which require accurate control of inelastic deformation. In order to address this limitation, a series of step-like NiTi samples with graded cross-sectional area were designed and fabricated. Multiple stress plateaus were achieved by varying the sample width and adjusting the number of steps; for instance, two and three stress plateaus were obtained in the samples with two and three steps, respectively. Also, linear force–strain response was obtained by changing gradually the width of the samples. The functional stability of the geometrically graded samples was significantly improved by incomplete recrystallization annealing (600 °C) followed by low-temperature (250 °C) aging treatment. The incompletely recrystallized specimens contained many dislocations and grain and sub-grain boundaries, which promoted the uniform precipitation of Ni4Ti3 nanoparticles during aging treatment. The homogeneously and densely dispersed Ni4Ti3 nanoparticles were able to strengthen the matrix considerably and prevent plastic activities during stress-induced martensite transformation. As a result, the functional stability of the geometrically graded NiTi samples was much improved. After aging at 250 °C for 120 h, all the samples showed a small residual strain of <1.0% after 20 loading–unloading cycles.

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