Chen, J., Zhao, C., Zhang, S., Zhang, W., Liu, W., Lei, L., Ramamurty, U., & Fang, G. (2024). Imparting high elastocaloric cooling potential to NiTi alloy by two-step enhancements. Materials Science and Engineering: A, 892, 146073. https://doi.org/10.1016/j.msea.2024.146073
Abstract:
The large adiabatic temperature change during the stress-induced phase
transformation in the superelastic NiTi alloy makes it a leading candidate material for
solid-state elastocaloric cooling applications. However, NiTi with a uniform grain
structure generally offers either large cooling capacity or low energy dissipation, but
not both. In an earlier study, we demonstrated that the alloy with graded grain sizes,
obtained using differential annealing of heavily cold-worked sheets, can overcome this
intrinsic limitation. However, non-transformable phases (residual martensite and
amorphous phases), which are introduced into the microstructure during cold rolling,
impair the full exploitation of the cooling potential of the graded NiTi. Here, we
introduce an intermediate processing step, namely post-deformation annealing, which
eliminates the undesirable phases while maintaining nanocrystallinity, before imparting a microstructural gradient. Results show that the synergy between various
microstructural elements results in a significant enhancement in the cooling capacity
while keeping the energy dissipation low. Moreover, the functional fatigue performance
of the graded alloy is also preferable to the conventional coarse-grained NiTi. The
micromechanical reasons behind these improvements are elucidated by recourse to
detailed experiments.
License type:
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Funding Info:
This research / project is supported by the Agency for Science, Technology and Research - Structural Metal Alloys Programme
Grant Reference no. : A18B1b0061