Unveiling oxidation-induced super-elasticity in metallic glass nanotubes

Oxidation can degrade the properties and performance of metals. Nevertheless, a analysis group co-led by scientists from Metropolis College of Hong Kong (CityU) not too long ago found that severely oxidized metallic glass nanotubes can attain an ultrahigh recoverable elastic pressure, outperforming most typical super-elastic metals. Additionally they found the bodily mechanisms underpinning this super-elasticity.

Their discovery implies that oxidation in low-dimension metallic glass may end up in distinctive properties for functions in sensors, medical units and different nanodevices. The findings had been revealed in Nature Supplies below the title “Oxidation-induced superelasticity in metallic glass nanotubes.”

Lately, the useful and mechanical properties of low-dimensional metals, together with nanoparticles, nanotubes and nanosheets, have garnered consideration for his or her potential functions in small-scale units, similar to sensors, nano-robots and metamaterials. Nevertheless, most metals are electrochemically energetic and prone to oxidation in ambient environments, which frequently degrades their properties and functionalities.

“Metallic nanomaterials have a excessive surface-to-volume ratio, which could be as much as 10⁸ m^-1. So in precept, they’re anticipated to be notably liable to oxidation,” mentioned Professor Yang Yong, within the Division of Mechanical Engineering at CityU, who led the analysis group collectively together with his collaborators.

“To make use of low-dimensional metals to develop next-generation units and metamaterial, we should totally perceive the hostile results of oxidation on the properties of those nanometals after which discover a method to overcome them.”

Due to this fact, Professor Yang and his group investigated oxidation in nanometals, and in sharp distinction to their expectation, they discovered that severely oxidized metallic glass nanotubes and nanosheets can attain an ultrahigh recoverable elastic pressure of as much as about 14% at room temperature, which outperforms bulk metallic glasses, metallic glass nanowires, and plenty of different super-elastic metals.

They made metallic glass nanotubes with a median wall thickness of simply 20 nm, and fabricated nanosheets from totally different substrates, similar to sodium chloride, polyvinyl alcohol and traditional photoresist substrates, with totally different ranges of oxygen focus.

They then performed 3D atom probe tomography (APT) and electron power loss spectroscopy measurements. Within the outcomes, oxides had been dispersed throughout the metallic glass nanotubes and nanosheets, in contrast to typical bulk metals, through which a strong oxide layer varieties on the floor. Because the oxygen focus within the samples elevated owing to metallic–substrate reactions, linked and percolating oxide networks had been fashioned contained in the nanotubes and nanosheets.

In-situ microcompression measurements additionally revealed that the severely oxidized metallic glass nanotubes and nanosheets exhibited a recoverable pressure of 10%–20%, which was a number of occasions greater than that of most typical superelastic metals, similar to form reminiscence alloys and gum metals. The nanotubes additionally had an ultra-low elastic modulus of about 20–30 GPa.

To grasp the mechanism behind this, the group performed atomistic simulations, which indicated that the superelasticity originates from extreme oxidation within the nanotubes and could be attributed to the formation of a damage-tolerant percolation community of nano-oxides within the amorphous construction. These oxide networks not solely limit atomic-scale plastic occasions throughout loading, but in addition result in the restoration of elastic rigidity on unloading in metallic glass nanotubes.

“Our analysis introduces a nano-oxide engineering method for low-dimensional metallic glasses. The morphology of nano-oxides inside metallic-glass nanotubes and nanosheets could be manipulated by adjusting the oxide focus, starting from remoted dispersions to a linked community,” mentioned Professor Yang.

“With this method, we are able to develop a category of heterogeneous nanostructured ceramic-metal composites by mixing metals with oxides on the nanoscale. Such composites have nice potential for numerous future industrial functions and nanodevices working in harsh environments, similar to sensors, medical units, micro- and nano-robots, springs and actuators,” he added.