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Title:Dislocation interactions with characteristic interfaces in Ag-Cu eutectic
Author(s):Eftink, Benjamin P
Director of Research:Robertson, Ian M
Doctoral Committee Chair(s):Robertson, Ian M
Doctoral Committee Member(s):Mara, Nathan; Lambros, John; Bellon, Pascal; Dillon, Shen
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Transmission electron microscopy (TEM)
Abstract:In the AgCu eutectic alloy, the observation of deformation twinning in Cu proposed to be induced by direct transmission of deformation twinning partial dislocations in Ag highlights the question of how interfaces in bi-phase materials respond to deformation. AgCu eutectic alloy was produced by both directional solidification and cast water-quenching. Control over processing variables enabled the synthesis of Ag/Cu eutectic with three predominant interface types: ones with a cube-on-cube orientation relationship with {111}Ag||{111}Cu interface habit planes, twin orientation relationship with {111}Ag||{111}Cu interface habit planes, and twin orientation relationship with near {3̅13}Ag||{1̅12}Cu interface habit planes. How dislocations interacted with each of the interfaces was determined using in situ and ex situ TEM straining experiments. It was determined that how strain transfers across Ag/Cu interfaces is consistent with criteria of strain transfer across grain boundaries in single phase materials. Specifically, the magnitude of the Burgers vector of the residual dislocation, |bres|, left in the interface should be small. This criterion was determining enough to drive Cu to twin under conditions where otherwise it would not. When transmission of a dislocation would result in a high |bres|, which is common for most slip systems encountering an incoherent twin interface, the interfaces were observed to block the dislocations. It was found that the increased effectiveness of the incoherent twin interfaces to block dislocations compared to the cube-on-cube interfaces resulted in an increased in the yield strength of the material. Interfaces with the cube-on-cube orientation relationship and mutual {111} interface plane between Ag and Cu results in transfer of twinning defects from Ag into Cu. This was found at length scales in the tens of nano-meters to the micron range. Twinning in both phases was observed after both split-Hopkinson pressure bar ex situ straining and tensile in situ straining. The cube-on-cube interfaces were still found to be barriers as dislocation pile-ups formed against the interfaces. Dislocation content at the interfaces increased as well after deformation. Incoherent and coherent twin interfaces between Ag and Cu were greater barriers to strain transfer than the cube-on-cube orientation relationship interfaces. Incoherent twin interfaces were found to allow perfect but not partial dislocation communication on the shared {111} slip plane across the interfaces due to the larger |bres| to communicate the partial dislocations. On the non-shared plane perfect and partial dislocations were blocked by the interfaces.
Issue Date:2016-02-22
Rights Information:Copyright 2016 Benjamin P. Eftink
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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