ABSTRACT
Despite various strategies to address sticking failure in stainless steels (STSs), difficulties in understanding its fundamental mechanisms hinder precise solutions during STS fabrication. This study investigated the effect of chromium (Cr) content on the microstructures and failure modes of oxide scales under a tensile load, simulating the hot-rolling process. The dynamic, real-time behavior of crack initiation, propagation, and interfacial delamination in the oxide scales under tension was analyzed using an in situ scanning electron microscopy (SEM) tensile test. With a high Cr content, iron (Fe) oxide and chromium(III) oxide (Cr2O3) form a layered structure, which is delaminated along the interfaces between the thin Cr2O3 layer and the bulk after perpendicular cracking. The saturated crack densities obtained from in situ SEM provide interfacial strength, while the elastic modulus and hardness obtained from nanoindentation provide vertical fracture strength. In combination with an ex situ elemental image analysis, the in situ SEM results reveal three different failure modes of the four different STSs. The results confirm that sticking failure is more likely to occur as the Cr content increases.
ABSTRACT
Both self-healable conductors and stretchable conductors have been previously reported. However, it is still difficult to simultaneously achieve high stretchability, high conductivity, and self-healability. Here, we observed an intriguing phenomenon, termed "electrical self-boosting", which enables reconstructing of electrically percolative pathways in an ultrastretchable and self-healable nanocomposite conductor (over 1700% strain). The autonomously reconstructed percolative pathways were directly verified by using microcomputed tomography and in situ scanning electron microscopy. The encapsulated nanocomposite conductor shows exceptional conductivity (average value: 2578 S cm-1; highest value: 3086 S cm-1) at 3500% tensile strain by virtue of efficient strain energy dissipation of the self-healing polymer and self-alignment and rearrangement of silver flakes surrounded by spontaneously formed silver nanoparticles and their self-assembly in the strained self-healing polymer matrix. In addition, the conductor maintains high conductivity and stretchability even after recovered from a complete cut. Besides, a design of double-layered conductor enabled by the self-bonding assembly allowed a conducting interface to be located on the neutral mechanical plane, showing extremely durable operations in a cyclic stretching test. Finally, we successfully demonstrated that electromyogram signals can be monitored by our self-healable interconnects. Such information was transmitted to a prosthetic robot to control various hand motions for robust interactive human-robot interfaces.
