In situ study of the initiation of hydrogen bubbles at the aluminium metal/oxide interface

Abstract

The presence of excess hydrogen at the interface between a metal substrate and a protective oxide can cause blistering and spallation of the scale. However, it remains unclear how nanoscale bubbles manage to reach the critical size in the first place. Here, we perform in situ environmental transmission electron microscopy experiments of the aluminium metal/oxide interface under hydrogen exposure. It is found that once the interface is weakened by hydrogen segregation, surface diffusion of Al atoms initiates the formation of faceted cavities on the metal side, driven by Wulff reconstruction. The morphology and growth rate of these cavities are highly sensitive to the crystallographic orientation of the aluminium substrate. Once the cavities grow to a critical size, the internal gas pressure can become great enough to blister the oxide layer. Our findings have implications for understanding hydrogen damage of interfaces.

Hydrogenated vacancies lock dislocations in aluminium

“…3b,c, two minor changes can be observed by comparing the image before and after the hydrogenation: tiny blisters appeared on the pillar surface (as indicated by black arrows) and a short curved dislocation segment became straight (as indicated by the white arrow). The former unequivocally proves that hydrogen has been introduced into the aluminium pillar29. The latter, on the other hand, cannot be simply attributed to the effect of hydrogen, considering that straightening of dislocation also occurred in the previous vacuum aging experiment (Fig.…”

“…The compression tests were carried out subsequently in vacuum and ∼2 Pa pure hydrogen gas. Before the tests in hydrogen environment, samples were hydrogenated under electron-beam intensity of ∼0.45 nA μm −2 in ∼2 Pa H 2 for about 30 min, which is long enough for hydrogen diffusion while not too long to cause obvious blistering on the pillar surface29. The dislocations inside the pillar roughly keep the same configuration during the charging process.…”

Nanometre-scale 3D defects in Cr2AlC thin films

“…Xie et al . 37 reported an in-situ observation of nanoscale gas bubbles at aluminium metal/oxide interface under the exposure of hydrogen in order to explain the commonly observed interfacial failure. Pruymboom et al .…”

Current status and future directions for in situ transmission electron microscopy

“…3–4 The design of in situ TEM holders have now progressed to the level that both strength and ductility can be quantified through compression, tension or bending experiments at low (−140 °C) or high (400 °C) temperatures. 5 It is now possible to make high resolution force measurement and control system. These, combined with improve sample geometries lead to new loading mechanisms, and new methods to measure stress and strain locally.…”

“…For example, the Delft group has used electron energy-loss spectroscopy (EELS) to measure local temperature, using change of gas density with temperature in windowed holder filled with 1.2 5 Pa of H 2 . 44 Resistivity measurements as implemented in the Delft-MEMS based holders seem to work quite well.…”