Mechanical behavior of crystals is dictated by dislocation motion in response to applied force. While it is extremely difficult to directly observe the motion of individual dislocations, several correlations can be made between the microscopic stress-strain behavior and dislocation activity. Here, we present for the first time the differences observed between mechanical behavior in two fundamental types of crystals: face-centered cubic, fcc (Au, Cu, Al, Ni, etc.) and body-centered cubic, bcc (W, Cr, Mo, Nb, etc.) with sub-micron dimensions subjected to in-situ micro-compression in SEM chamber. In a striking deviation from classical mechanics, there is a significant increase in strength as crystal size is reduced to 100nm; however in gold crystals (fcc) the highest strength achieved represents 44% of its theoretical strength while in molybdenum crystals (bcc) it is only 7%. Moreover, unlike in bulk where plasticity commences in a smooth fashion, both nano-crystals exhibit numerous discrete strain bursts during plastic deformation. These remarkable differences in mechanical response of fcc and bcc crystals to uniaxial micro-compression challenge the applicability of conventional strain-hardening to nano-scale crystals. We postulate that they arise from significant differences in dislocation behavior between fcc and bcc crystals at nanoscale and serve as the fundamental reason for the observed differences in their plastic deformation. Namely, dislocation starvation is the predominant mechanism of plasticity in nano-scale fcc crystals while junction formation and subsequent hardening characterize bcc plasticity, as confirmed by the microstructural electron microscopy. Experimentally obtained stress-strain curves together with video frames during deformation and cross-sectional TEM analysis are presented, and a statistical analysis of avalanche-like strain bursts is performed for both crystals and compared with stochastic models.
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ASME 2008 9th Biennial Conference on Engineering Systems Design and Analysis
July 7–9, 2008
Haifa, Israel
Conference Sponsors:
- International
Volume 1: Advanced Energy Systems; Advanced and Digital Manufacturing; Advanced Materials; Aerospace
ISBN:
978-0-7918-4835-7
PROCEEDINGS PAPER
In-Situ Investigation of Plasticity at Nano-Scale Available to Purchase
Julia R. Greer,
Julia R. Greer
California Institute of Technology, Pasadena, CA
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Ju-Young Kim,
Ju-Young Kim
California Institute of Technology, Pasadena, CA
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Steffen Brinckmann
Steffen Brinckmann
California Institute of Technology, Pasadena, CA
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Julia R. Greer
California Institute of Technology, Pasadena, CA
Ju-Young Kim
California Institute of Technology, Pasadena, CA
Steffen Brinckmann
California Institute of Technology, Pasadena, CA
Paper No:
ESDA2008-59117, pp. 519-520; 2 pages
Published Online:
July 6, 2009
Citation
Greer, JR, Kim, J, & Brinckmann, S. "In-Situ Investigation of Plasticity at Nano-Scale." Proceedings of the ASME 2008 9th Biennial Conference on Engineering Systems Design and Analysis. Volume 1: Advanced Energy Systems; Advanced and Digital Manufacturing; Advanced Materials; Aerospace. Haifa, Israel. July 7–9, 2008. pp. 519-520. ASME. https://doi.org/10.1115/ESDA2008-59117
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