Engineering heterophase interface for improving fatigue resistance in Ag-based gradient nanolayered films

Nanocrystalline metal films are indispensable as conductors in flexible electronics, yet their electrical functionality is frequently compromised by poor fatigue resistance. We propose a gradient nanolayered (GNL) architecture strategy to enhance the fatigue performance of nanocrystalline Ag films. Through a synergistic combination of fatigue experiments, microstructural analyses and molecular dynamics simulations, we systematically compare the fatigue behavior of two Ag/X ( X = Al, Mo) GNL systems. Our results demonstrate that fatigue life and damage mechanisms are critically governed by heterophase interface characteristics. The Ag/Al GNL films exhibit exceptional fatigue resistance, with a fatigue life improvement exceeding two orders of magnitude. This enhancement arises from highly stable coherent Ag/Al interfaces, which suppress grain coarsening, alleviate interfacial stress concentration, and promote crack deflection, thereby delaying crack initiation and impeding crack propagation. In contrast, the Ag/Mo GNL films show only a modest (∼ 3-fold) improvement due to the instability of their semi-coherent interfaces, where interfacial shearing and void formation dominate failure. We elucidate this disparity by establishing a direct correlation between damage mechanisms, interface stability, and the crystallographic misorientation of adjacent Ag layers across the heterophase interface. These findings establish GNL architectures as a promising design concept for developing fatigue-resistant metal films in flexible electronics.