Activation Volume Determination in FCC Nanopillars
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Authors
Tucker, Megan E.
Date
Type
thesis
Language
eng
Keyword
Activation volume , Nanopillars , Electron-beam lithography , In-Situ Compression Testing
Alternative Title
Abstract
Activation volume (V*) is a fundamental parameter describing thermally activated flow processes in crystalline materials. Its determination is fundamentally defined by the stress response to an instantaneous change in the inelastic strain rate. V* values were measured for polycrystalline nickel (Ni) and copper (Cu) nano-pillars, fabricated in-house by electron beam lithography and electroplating processes, using a new strain rate change test procedure developed for FemtoTool’s FT-NMT03, an in-situ nanomechanical testing apparatus. Pillars were compressed in a scanning electron microscope at temperatures of 300 ± 1 K operating the FT-NMT03 in displacement control at a base nominal strain rate of 0.004 s-1 with rate change factors of 1/4 or 1/10. The instrument response replicates the step-ramp rate change method developed previously at Queen’s for large-scale specimen testing. Continuous rate tests, which are typical in the literature, were also made to compare to rate change results. V* values for ¼ rate change tests on Cu were found to be 35.4 ± 2.4 b3 and 34.4 ± 1.3 b3, and for 1/10 rate change tests, found to be 17.3 ± 2.0 b3 and 29.9± 2.0 b3 with or without step-ramp compensation, respectively. V* for factor of four continuous rate tests on Ni were 2.4 ± 0.1 b3 on average. V* values for 1/4 change tests on Ni were 28.3±2.6 b3, and 29.4±3.0 b3, and for 1/10 change tests on Ni were 27.6 ± 1.3 b3 and 21.0 ± 2.5 b3 with and without steps, respectively. It was determined that step compensation did not significantly impact measurements with the FT-NMT03 compared to those made without compensation for low-factor rate changes, but for rate change factors of 10 or greater, tests without compensation underestimated V* enough to alter conclusions about rate-controlling mechanisms. This work validates the step-ramp method for V* determination and the uncertainty in data previously reported in the nano-pillar literature.
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ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NonCommercial-NoDerivatives 4.0 International