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In situ transmission electron microscopy He+ implantation and thermal aging of nanocrystalline iron

Journal of Nuclear Materials

Muntifering, Brittany R.; Fang, Youwu; Leff, Asher C.; Dunn, Aaron; Qu, Jianmin; Taheri, Mitra L.; Dingreville, Remi P.; Hattar, Khalid M.

Due to their high density of interfaces, nanostructured material are hypothesized to show a higher tolerance to radiation damage compared to conventional coarse-grained materials and are on interest for use in future nuclear reactors. In order to investigate the roles of vacancies, self-interstitials, and helium during defect accumulation, and the thermal evolution of such defects, a complex set of in situ TEM experiments were performed in nanocrystalline iron.

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TYPE Journal Article YEAR 2016
DOIOSTI

High Cycle Fatigue in the Transmission Electron Microscope

Nano Letters

Bufford, Daniel C.; Stauffer, Douglas; Mook, William M.; Syed Asif, S.A.; Boyce, Brad B.; Hattar, Khalid M.

One of the most common causes of structural failure in metals is fatigue induced by cyclic loading. Historically, microstructure-level analysis of fatigue cracks has primarily been performed post mortem. However, such investigations do not directly reveal the internal structural processes at work near micro- and nanoscale fatigue cracks and thus do not provide direct evidence of active microstructural mechanisms. In this study, the tension-tension fatigue behavior of nanocrystalline Cu was monitored in real time at the nanoscale by utilizing a new capability for quantitative cyclic mechanical loading performed in situ in a transmission electron microscope (TEM). Controllable loads were applied at frequencies from one to several hundred hertz, enabling accumulations of 106 cycles within 1 h. The nanometer-scale spatial resolution of the TEM allows quantitative fatigue crack growth studies at very slow crack growth rates, measured here at ∼10-12 m·cycle-1. This represents an incipient threshold regime that is well below the tensile yield stress and near the minimum conditions for fatigue crack growth. Evidence of localized deformation and grain growth within 150 nm of the crack tip was observed by both standard imaging and precession electron diffraction orientation mapping. These observations begin to reveal with unprecedented detail the local microstructural processes that govern damage accumulation, crack nucleation, and crack propagation during fatigue loading in nanocrystalline Cu.

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TYPE Journal Article YEAR 2016
DOIOSTIScopus
Results 326–350 of 612
Results 326–350 of 612