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Title:Role of interfaces on severe plastic deformation and He-irradiation tolerance in Cu-Nb nanocomposites
Author(s):Lach, Timothy G
Director of Research:Bellon, Pascal
Doctoral Committee Chair(s):Bellon, Pascal
Doctoral Committee Member(s):Averback, Robert S; Dillon, Shen J; Stubbins, James F
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Immiscible metal nanocomposites
severe plastic deformation
Abstract:Interface structure in immiscible metal nanocomposites plays a key role in deformation tolerance and radiation damage tolerance. Interface structure, just like microstructure, can vary within the same material system depending on the processing route; the properties of a material can also vary depending on the interface structure. The role of interface structure on the tolerance to severe plastic deformation in Cu-Nb nanocomposites was investigated by comparing the microstructural evolution after high pressure torsion (HPT) of multilayer nanocomposites grown by physical vapor deposition (PVD) with low shear strength interfaces and fabricated by accumulative roll bonding (ARB) with high shear strength interfaces. And the role of interface structure on the trapping of He was studied by comparing He-bubble formation in nano-multilayers grown by PVD, nanolaminates fabricated by ARB, and three-dimensional nanocomposites obtained by high pressure torsion (HPT); each of these has a different preferred orientation relationship. The stability of PVD-grown multilayers when subjected to HPT is significantly better to high shear strain than the ARB-fabricated multilayers. The PVD-grown multilayers remain largely stable up to a strain of ~81 and still have regions of multilayers at a strain of ~357 before transforming to a 3D nanocomposite by a strain of ~685; the ARB multilayer composites meanwhile become unstable at shear strain of ~10 and completely transform to a 3D interconnected composite at a strain of ~278. The mechanisms for deformation depend on the interface character; the PVD-grown material with low shear strength interfaces deform by interfacial sliding while the ARB-fabricated material deforms by dislocation glide across the interface. In both layered systems, there is kink and shear banding of layers at higher shear strain that changes the local orientation of layers relative to the shear direction resulting in a route to transition to a 3D nanocomposite structure. Likewise under He-ion irradiation, the critical He dose per unit interfacial area for bubble formation was largest for the PVD multilayers, lower by a factor of ~1.4 in the HPT nanocomposites annealed at 500 ˚C, and lower by a factor of ~4.6 in the ARB nanolaminates relative to the PVD multilayers. The high concentration of free volume at interfaces in PVD-grown multilayers is excellent for trapping He atoms and point defects, and the amount of trapped He at the interface scales with interface area density. A combination of efficient interfaces and high density of interfaces is ideal for trapping He atoms and point defects. The results of both high shear strain using HPT and He implantation indicate that the (111)FCC||(110)BCC Kurdjumov-Sachs (KS), or {111}KS, interfaces predominant in PVD provide more effective traps for both point and line defects than the {112}KS interfaces predominant in ARB nanolaminates. The steady-state microstructural stability, good trapping efficiency, and high interface area of 3D structures processed by severe plastic deformation make them most attractive for structural applications such as nuclear energy.
Issue Date:2016-01-27
Rights Information:Copyright 2016 Timothy Lach
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05

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