Controlling Fatigue Cracks in the Transmission Electron Microscope.

Fatigue cracking in materials is a widespread engineering challenge with substantial economic and safety consequences. In situ Transmission Electron Microscopy (TEM) is an emerging method to investigate the nanoscale origins of fatigue. Recent nanoindenter-based methods enabled detailed observation of crack propagation in the TEM, yet these experiments remain difficult to control. Here, a novel control methodology adopted from linear elastic fracture mechanics employs a stress intensity factor K to quantify the driving force acting on propagating fatigue cracks in the TEM. This present method, demonstrated here on nanocrystalline Pt alloys, provides a quantitative basis to compare response of different materials. Controlling crack growth over many micrometers for in situ TEM fatigue experiments also unlocks an ability to observe nanoscale damage mechanisms including crack blunting, closure, deflection, branching, healing, and fatigue-induced grain growth. Such an approach is readily extensible to investigate the nanoscale origins of cyclic degradation in both bulk structural materials and in functional nanotechnology applications such as micro-/nano-electronic components, MEMS (micro-electro-mechanical systems) devices, flexible electronics, and thin film applications.