Endowing low fatigue for elastocaloric effect by refined hierarchical microcomposite in additive manufactured NiTiCuCo alloy

NiTiCu-based shape memory alloys have been considered as ideal materials for solid-state refrigeration due to their superb cycling stability for elastocaloric effect.However,the embrittlement and deterioration caused by secondary phase and coarse grains restrict their applications,and it is still challenging since the geometric components are required.Here,bulk NiTiCuCo parts with excellent forming quality were fabricated by laser powder bed fusion(LPBF)technique.The as-fabricated alloy exhibits refined three-phases hierarchical microcomposite formed based on the rapid cooling mode of LPBF,composed of intricate dendritic Ti2Ni–NiTi composite and nano Ti2Cu embedded inside the NiTi-matrix.This configuration endows far superior elastocaloric stability compared to the as-cast counterpart.The low fatigue stems from the strong elastic coupling between the interphases with reversible martensite transformation,revealed by in-situ synchrotron high-energy x-ray diffraction.The fabrication of NiTiCuCo alloy via LPBF fills the bill of complex geometric structures for elastocaloric NiTiCu alloys.The understanding of interphase micro-coupling could provide the guide for designing LPBF fabricated shape memory-based composites,enabling their applications for special demands on other functionalities.

Proof of concept of a self-tightening needle-less suture using a NiTi shapememory alloy

Among surgical procedures,suturing is considered simple.However,in some situations,suturing is not easy or feasible.Here,we present proof of concept of a new self-tightening needle-less suture made of a NiTi alloy.The new device is designed to overcome two demanding steps of traditional suturing:needle introduction and manual knotting.Our novel suture is composed only of a short NiTi wire that is able to change shape by exploiting a thermoelastic phase transition.This shape change is achieved by increasing the temperature from that of the operating room(e.g.,20-22℃)to 32℃using warm water.Suturing consists of two steps:suture introduction,in which the suture is in an open configuration,and shape recovery(i.e.,closed configuration).The closed configuration is maintained at human body temperature thanks to peculiar pseudoelastic properties of the NiTi material.Finally,thermal and functional characterization verified the simplicity and effectiveness of the proposed device.

Kinetic equations characterizing double reversible transformations in heating CuZnAlMnNi shape memory alloy

The apparent activation energies and frequency factors of thedouble reversible transformations occurring in heating CuZnAlMnNIshape memory alloy (SMA) were deduced as ΔE_x→M = 62. 597 8 KJ/mol, ΔE_M → A = 153. 92 KJ/Mol, A_x→M = 5.2232 × 10~9S^-1, andA_ M → A = 2.3251 × 10~23 S^-1, respectively. The kinetic equationsof the two transformations due- Ing heating were establishedsimultaneously.