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>Canada and NATO Operations:Examining the ‘middle power’ narrative and its influence on Canadian foreign policy in NATO’s Afghanistan and Libya operations
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Canada and NATO Operations:Examining the ‘middle power’ narrative and its influence on Canadian foreign policy in NATO’s Afghanistan and Libya operations
Nickel-based superalloys are high performance structural materials that exhibitexcellent strength and creep resistance at high temperatures, even inchemically aggressive environments. This makes them ideal for use in theconstruction of ecient turbines for energy generation or aerospace applications.These superalloys are usually manufactured as single crystals, withtheir high strength resulting from dislocation pinning at interfaces betweenthe fcc matrix an L12-ordered precipitates. Chemical impurities such asrhenium also aect dislocation mobility, and their inclusion in commercialmaterials is standard practice. However, there is currently no detailed understandingof the atomic-scale mechanisms underlying these processes. Thisproblem is here addressed at the atomistic level. The typical accuracy level ofrst principle methods is required to describe bond breaking in the distortedregion surrounding a dislocation core and for including impurities in the fccmatrix, but model systems must be large enough to accommodate the straingradients typical of long-range elastic interactions due to the presence ofdislocations. Multiscale methods are therefore required for simulating thesechemo-mechanical processes. The `Learn on the Fly' (LOTF) technique is anon-uniform precision quantum mechanical/molecular mechanical approach.It oers a predictor/corrector algorithm for speeding up calculations, and thepossibility of modelling a moving quantum region, useful for fast dislocationmotion due to high simulating temperature or load condition. The scope ofthis thesis is to apply this method to metallic systems to conduct, for the rsttime, quantum mechanical accurate simulations of dislocation motion in Nibasedalloys. The QM/MM method corrects the deciencies of the classicalinteratomic potential related to inaccurate energetics for the hcp phase, relevantto the geometry of dislocation cores, and it is capable of reproducing thecorrect separation between Shockley partials at high temperature conditions.
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