April 28, 2016 @ 12:00 pm - 1:00 pm
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The plasticity of highly oriented nano-layered Zr/Nb composites
Over the years, two-phase nanolaminate thin film composites have demonstrated an unusually broad number of desirable properties, such as high strength, high strain to failure, thermal stability, and resistance to light-ion radiation. Recently we have shown that bi-phase HCP/BCC (Zr/Nb) nanolaminates with layer thicknesses < 50 nm can be made via severe plastic deformation (SPD) in bulk sizes suitable for structural applications. Moreover, mechanical testing of these Zr/Nb nanolaminates shows exceptionally high strength, and microstructural characterization, via a suite of techniques, indicates that the crystals are highly oriented, unlike conventionally rolled Zr or Nb. While the cause of these unusual properties can intuitively be associated with a high density of Zr/Nb interfaces, how these interfaces physically control microstructural and texture evolution, and in turn, affect the macroscopic properties, remain areas of intense research.
This presentation highlights our modeling and experimental efforts to understand the linkages between the evolution of the nanostructure, interface properties, and preferred texture that occur during SPD processing. Specifically we employ a spatially resolved multiscale 3D crystal plasticity based model to study the orientational stablity of Zr single crystals and Zr/Nb bicrystals during rolling deformation. The model allows for slip to occur on all possible available slip modes in Zr and Nb and is able to directly relate texture evolution to the relative contributions of these different slip modes. The analysis indicates that Zr crystals, when bonded to Nb crystals, become less orientationally stable than the same single crystal Zr orientation under the same deformation state. With these calculations, we find that special peak texture components that arise only at the nanoscale are due to substantially reduced ratios of CRSS ratios among the prismatic, pryamidal <c+a>, and basal slip systems. Although we focus this study on nanocrystalline Zr, the insight gained can be applied to similar nanostructuring efforts of other HCP metals via SPD processes.
Seminar will be held in Hackerman Hall, B-17 from 12-1 PM.