Classic theories on fatigue damage in bulk metals have been extensively studied, but little is understood about the fundamental fatigue mechanisms at submicron and nanometer scales where dislocation pattern formation is completely inhibited. Recently, Prof. ZHANG Guangping and his research team from Institute of Metal Research, Chinese Academy of Sciences, have revealed the vacancy-dominated fatigue mechanism at smaller scales by quantitatively analyzing fatigue damages. Their work has been published in Acta Materialia.

In this work, they found that although no typical persistent slip band-like dislocation patterns could be found in Au films with h=930 nm ~ 90 nm, severe fatigue extrusion/intrusion behaviors can also be observed in those thin films. Unexpectedly, the relative extrusion height increases with decreasing the film thickness, and it is even thousand times larger than that of bulk-scale single and polycrystals, but the fatigue resistance or fatigue life of the small-scale thin films is higher than that of the bulk-scale ones. Combining the detailed characterizations of fatigue damages and vacancy defects with theoretical calculations, continuous generation and migration of vacancies is proved to be crucial for the shape of extrusion/intrusions and kinetics of their growth at submicron and even nanometer scales. The discovery of the vacancy-dominated fatigue mechanism at small scales expands our comprehension of metal fatigue mechanisms to submicron and even nanometer scales. Furthermore, it proposes an innovative interface engineering approach through the modulation of vacancy behavior for fatigue-tolerant materials, including composite current collectors for new energy batteries, flexible electronic devices, and mechanical components in microelectromechanical systems (MEMS).

Schematic diagram of fatigue damage mechanisms in metals with different length scales. (Image by IMR)