Experimental validation of a one-dimensional model for monolithic shape memory alloys with multiple pseudoelastic plateaus

Michael, A.; Zhou, Y.; Khan, Muhammad

doi:10.1177/1045389x15620044

Cited by 7 publications

(1 citation statement)

References 44 publications

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“…By alternately varying two sets of process parameters [29] or using a repetitive scanning strategy [30] to regulate the Ni evaporation, NiTi alloys with a compositional gradient were prepared using laser powder bed fusion techniques. Similarly, local heat treatment of Ni-rich NiTi wire by laser processing resulted in more pronounced vaporization of Ni than Ti, and thus a multi-stage SIM plateau could be achieved [31]. By welding NiTi wires with different compositions into a single unit along their length, a sample with graded transformation temperatures and graded critical stress for SIM was achieved [32].…”

Section: Introductionmentioning

confidence: 99%

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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Section: Introductionmentioning

confidence: 99%

Superelasticity of Geometrically Graded NiTi Shape Memory Alloys

Chen,

Xi,

Jiang

et al. 2023

Metals

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Effects of post-processing on the thermomechanical fatigue properties of laser modified NiTi

Panton

Michael

Zhou

et al. 2019

International Journal of Fatigue

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The multifunctional capabilities needed for advanced shape memory alloys (SMA) actuators has been shown to be achievable by locally tuning the properties through laser processing. Before the wide-spread use of these SMAs is realized, a detailed understanding on the long-term stability and functional life span of these material must be achieved. The current study systematically investigates the effects of thermomechanical treatment on laser modified NiTi wires, while comparing them to the original base material. Surface analysis was done using a scanning electron microscope (SEM), while microstructure analysis was performed using transmission electron microscopy (TEM). Mechanical properties were assessed using standard tensile tests and a custom built thermomechanical fatigue. Results showed that the coarse-grains, large precipitates and surface defects associated with as laser modified NiTi resulted in reduced mechanical performance. However, subsequent thermomechanical treatment restored the refined microstructure and mechanical performance similar to the base material while providing the added functionality.

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