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Center for Nonlinear Studies |
Nano-layered metallic composites containing a very high density of heterophase interfaces (interphase boundaries) exhibit extraordinary resistance to damage induced by extreme loading and environments. Such materials are dominated by the unusual physical and functional properties of the interfaces. At Los Alamos, we have a few programs dedicated to a multi-scale understanding of the role that interfaces between two dissimilar metals play in plastic deformation and ultimately structural performance of metallic composites. After introducing these programs in brief, I will focus on the two-phase Ag-Cu composite material system and the role of the Ag-Cu interface in facilitating extensive deformation twinning in Cu during room temperature, low strain-rate loading conditions. Deformation twinning is difficult in single-phase Cu, usually requiring extreme conditions, such as shock and/or cryogenic temperatures, or grain sizes a few tens of nanometers or less. Using TEM analyses, atomistic simulation, and dislocation theory, our study on deformed Ag-Cu reveals two ways in which the inter-phase boundary can promote twinning in Cu, with the added significance that such assistance does not require extreme stresses associated with shock loading, cold temperatures, very fine nm length scales, or severe stress concentrators, like cracks. Notably, the proposed mechanisms can explain the observed Ag-Cu interface transformation from the low energy {111}-type habit plane to a new {100}-type plane and the fine secondary twins in both Ag and Cu that result from deformation. Interface-driven twinning as revealed by this study suggests the exciting possibility of controlling composite material behavior through the design of hetero-phase interface structure and properties.
Host: Eddy Timmermans, CNLS, eddy@lanl.gov, 5-8306