RESPONSE OF BULK CU-NB NANOLAMELLAR COMPOSITES TO SEVERE ROLLING STRAINS
In bulk multi-phase composite metals containing an unusually high density of heterophase interfaces, the bi-meta! interface controls all defect-related processes. Quite unconventionally, the constituent phases play only a secondary role. With the right characteristics, these bi-material interfaces can possess significantly enhanced abilities to absorb and eliminate defects. 1-3 Through their unparalleled ability to mitigate damage accumulation induced under severe loading and/or severe environments, they will provide their parent composite with a highly effective healing mechanism and consequently a robustness not possible in existing advanced structural materials. Todays bulk synthesis techniques and materials models,however, are unprepared to treat materials that are dominated by bi-metal interfaces. Consequently we cannot fabricate interface-dominant composites with the needed interfacial properties. In this work, we approach this problem by developing a predictive and experimentally validated model that holds the unique capability to predict the evolution of the interfacial structure and behavior during bulk large strain deformation. To succeed in this pioneering effort, we will spearhead new and creative ways to overcome the areas in which current methodologies are the weakest梚n linking length scales over the so-called micron gap and accounting for the special roles of bi-metal interfaces. This innovative multi-scale predictive capability will for the first time offer a tool to address materials falling within the new paradigm of interface dominance and to predict the synthesis routes needed for a targeted set of desired interfacial properties. Bulk (> cm3) laminar composites with controllable layer thicknesses down to the submicron or nano-scale range can be fabricated via accumulative roll bonding (ARB), a severe plastic deformation (SPD) processing technique. The ARB process itself is an extreme condition. Imposing over thousands of percent strain, ARB refines the microstructure of ordinary coarse-grained composite metals down To submicron and nanoscales. ARB is an ideal model material processing to submicron and nanoscales. ARB is an ideal model material processing technique for three reasons:1) it produces a 2-D layered microstructure, 2) it imposes monotonic deformation in a familiar manner (rolling), and 3) it allows for controllable accumulated strain and layer thickness (from 1 mm to 10 nm). However, the bi-metal interface parameter space and number of possible synthesis pathways are prohibitively large for effective experimental investigation. Manipulating the ARB process to achieve extraordinary interface properties requires a multi-scale predictive model that forecasts the evolution of interfacial properties (nm) during the bulk forming process (> cm). To solve this, we couple a predictive modeling effort with our experimental investigation to aid in navigation of the enormous experimental parameter space. In this presentation, we report on the plastic deformation mechanisms in Cu-Nb lamellar nanocomposites processed via Severe Plastic Deformation. In the Cu-Nb system, it has been found that at individual layer thicknesses of 40 nm and above, physical vapor deposited foils can be rolled to large strains. However, when the layer thickness decreases to ~5nm. the onset of shear instability during rolling limits ductility. In this work, we show the effects of cladding 5nm Cu/Nb multilayers with 40 nm Cu/Nb multilayers to limit the onset of geometric instability, thereby facilitating the deformation of 5nm Cu/Nb multilayers to large rolling strains. 4 Based on these findings, we utilize Accumulative Roll-Bonding (ARB) to process bulk Cu-Nb nanolamellar composites from 1 mm thick high-purity polycrystalline sheet into nanocomposites with layer thicknesses below 100 nm. This processing technique has the advantage of producing bulk quantities of nanocomposite material, and also exposes the interface and bulk constituents to large strains (1000s of percent). These extreme strains result in rolling textures and interfacial defect structures very different from those seen in nanolamellar composites grown via Physical Vapor Deposition methods. 5 It is found that interfacial content controls deformation processes at diminishing length scales, and is directly influenced by defect/interface interactions at the atomic scale. The authors acknowledge support provided in part by the Center for Materials at Irradiation and Mechanical Extremes, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number 2008LANL1026 and the Los Alamos National Laboratory Directed Research and Development (LDRD) project DR20110029.
nanomechanical behavior nanocomposite severe plastic deformation nanolayered composite rolling deformation
N.A.Mara J.Ledonne T.Wynn J.Carpenter J.Wang I.J.Beyerlein
Los Alamos National Laboratory,MS-K771, Los Alamos, New Mexico, 87545, USA Materials Science and Engineering Department, Carnegie Mellon University,Pittsburgh, Pennsylvania, U
国际会议
The Third International Conference on Heterogeneous Material Mechanics(第三届国际非均匀材料力学会议)
上海
英文
158-159
2011-05-22（万方平台首次上网日期，不代表论文的发表时间）