Elastocaloric effect of laser powder bed fused NiTi alloy with customizable hierarchical heterogeneous microstructure

Laser powder bed fusion (LPBF) technology not only allows the complex macro-structures fabrication, but also has the potential of flexible spatial microstructure controllability. For functional materials, slight modifications in the microstructure could significantly affect the macroscopic functionality. In this work, we showed how to break the trade-off between cooling capacity and efficiency in the elastocaloric effect by hierarchical heterogeneous microstructures NiTi shape memory alloys fabricated by LPBF in-situ remelting strategy. By applying different laser scanning strategies to different sub-regions of the preformed block, NiTi alloys with alternating ‘coarse-fine’ grain sizes were fabricated. The two samples were also independently prepared by using the sub-area process strategy for comparative study purposes. The results indicate that the hierarchical heterogeneous microstructure NiTi alloys acquire a stepwise gradient phase transformation behavior, which leads to an additional 38 % enhancement of their phase transformation enthalpy. Furthermore, the hierarchical heterogeneous microstructure sample exhibits a 38.5 % decrease in energy dissipation and a 52.3 % increase in elastocaloric efficiency with almost no cooling capacity loss compared to samples with a homogeneous microstructure. This work inspires the fabrication of high-performance materials with artificial microstructures via LPBF. This fabrication approach has significant potential to develop promising green, high-efficiency NiTi elastocaloric components. © 2024 Elsevier B.V.