Shape memory alloys (SMAs)
Research techniques: Micro/ nano-scale evaluation, elevated temperature evaluation, fatigue, creep and fracture evaluation, simulation and experimental modeling, material imaging and characterization, etc.
Shape memory alloys (SMAs) is one of the materials that is already widely used in many bulk scale applications like medical implants, braces, spring etc. and is still currently attracting numerous interests in small-scale applications. What’s unique about this material is that unlike other metallic alloys, shape memory alloys are able to change their shape between the austenitic phase and martensitic phase accordingly based on temperature and stress variations. This has allowed it to exhibit two unique mechanical behaviours, which are known as the shape memory effect and superelasticity. If we deform the material at lower temperatures, the material will be able to return back to its original shape when we heat it back up to form austenitic phase. This behaviour is also known as the shape memory effect. On the other hand, if we deform the material at higher temperatures, the material will return back to its original shape once the deformation force is released, exhibiting what we called superelasticity.
Amongst all the different types of SMAs, nickel-titanium (NiTi-) alloys stand out due to its excellent biocompatibility and mechanical performances. However, integration of this material in the form of thin films is still deemed difficult due to its high compositional sensitivity and reduced superelastic strain. This challenge have then made it crucial to precisely control the fabrication parameters in order to deposit thin films with desirable compositions and properties. This has also no doubt increased the difficulty to accurately evaluate its mechanical properties at small-scales.
Our research works focus on fabrication and the mechanical evaluation of the NiTi alloy in micro/ nano-scales, with great emphasis put on understanding the compositional effects through combinatorial studies, assessment of the deformation mechanisms under monotic and cyclic loading, improving simulation models, and evaluating its behaviors at elevated temperatures. These efforts would provide valuable insights in the fields of flexible electronics, elastocaloric devices, actuators and sensors, etc.
Shape memory alloys (SMAs) is one of the materials that is already widely used in many bulk scale applications like medical implants, braces, spring etc. and is still currently attracting numerous interests in small-scale applications. What’s unique about this material is that unlike other metallic alloys, shape memory alloys are able to change their shape between the austenitic phase and martensitic phase accordingly based on temperature and stress variations. This has allowed it to exhibit two unique mechanical behaviours, which are known as the shape memory effect and superelasticity. If we deform the material at lower temperatures, the material will be able to return back to its original shape when we heat it back up to form austenitic phase. This behaviour is also known as the shape memory effect. On the other hand, if we deform the material at higher temperatures, the material will return back to its original shape once the deformation force is released, exhibiting what we called superelasticity.
Amongst all the different types of SMAs, nickel-titanium (NiTi-) alloys stand out due to its excellent biocompatibility and mechanical performances. However, integration of this material in the form of thin films is still deemed difficult due to its high compositional sensitivity and reduced superelastic strain. This challenge have then made it crucial to precisely control the fabrication parameters in order to deposit thin films with desirable compositions and properties. This has also no doubt increased the difficulty to accurately evaluate its mechanical properties at small-scales.
Our research works focus on fabrication and the mechanical evaluation of the NiTi alloy in micro/ nano-scales, with great emphasis put on understanding the compositional effects through combinatorial studies, assessment of the deformation mechanisms under monotic and cyclic loading, improving simulation models, and evaluating its behaviors at elevated temperatures. These efforts would provide valuable insights in the fields of flexible electronics, elastocaloric devices, actuators and sensors, etc.
Read more in our publications:
[1] Lee, Z. F., Ryu, H., Kim, J. Y., Kim, H., Choi, J. H., Oh, I., Sim, G. D. (2024). High-throughput membrane deflection characterization of shape memory alloy thin films. Materials Science and Engineering: A, 892, 146028.
[2] Choi, J. H., Zaki, W., & Sim, G. D. (2023). Size-dependent constitutive model for shape memory alloys based on couple stress elastoplasticity. Applied Mathematical Modelling, 118, 641-664.
[1] Lee, Z. F., Ryu, H., Kim, J. Y., Kim, H., Choi, J. H., Oh, I., Sim, G. D. (2024). High-throughput membrane deflection characterization of shape memory alloy thin films. Materials Science and Engineering: A, 892, 146028.
[2] Choi, J. H., Zaki, W., & Sim, G. D. (2023). Size-dependent constitutive model for shape memory alloys based on couple stress elastoplasticity. Applied Mathematical Modelling, 118, 641-664.
Updated on 2024.04.19
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