Dec 24

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MRS Conference Fall 2014

Prof Budiman presented in two conferences at the MRS Conference 2014 held at Boston, MA.Both presentations are research work from Ihor Radchenko and Karthic R. Narayanan. Check out the details.

GG8.05 Design of Online, Real-Time, Non-Invasive Strain and Radiation Sensing Devices Using Novel Composite Nanomaterials











There are much technological interest as well as strategic opportunities in the recent years in the nanoscale multilayered composite materials due to their unusual mechanical properties such as very high flow strength, ultralight weight and stable plastic flow to large strains, as well as extreme radiation damage tolerance, and thus their great potential applications in the next generation energy technologies as well as in transportation, defense, biomedical, aerospace and space applications. Nanoscale multilayers represent a class of novel composite nanomaterials in which there arises rare opportunities to design new materials from the ground up and to tailor their properties to suit exactly their performance requirements – the holy grail of the modern materials science. This is becoming a reality due to the confluence of two recent advances in nanoscale materials processing and characterization technologies allowing construction and manipulation of microstructural building blocks of materials such as interfaces, grain boundaries and ultrathin films consisting of practically just a few layers of atoms. In this research, we design new nanoscale multilayered composite materials through atomic engineering of the interfaces leading to a high performance coating for both mechanical passivation as well as for radiation and strain sensing capabilities. The latter could lead to highly functional coating with real time, online, non-invasive monitoring capability of radiation and mechanical strains which could be critical for key components for instance in aerospace and space technologies/systems as well as for biomedical applications (for instance, strain monitoring for stents). As defects in nanolayers are accumulated in the interfaces, the interfaces become more and more disordered due to higher and higher concentrations of defects (dislocations, bubbles). We have preliminary evidence that dislocation density increases linearly with strain up until ~ 4% of strain. This represents an extended linear regime that we could take advantage for sensing of strains, and by extension of the same principles, of radiation damage. Preliminary evidence will be presented and initial design of novel nanolayers discussed.


RR9.05 Insights Into Mechanics of Nanoscale Cu/Nb Multilayers: Plasticity and Fracture

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From published studies of A.Misra et al., N.Mara et al. etc.., multilayer Cu/Nb composites have already proved to be one of the promising materials which can be subjected to extreme environments involving high radiation damage, temperature and mechanical loading. This idea of using nanolayers where Frank-Read source does not operate in a single layer, to build a strong solid was proposed by Koehler. The mechanical strengths of these Cu/Nb nanolayer composites have found to reach as high as ~2.5 GPa with a ductility of ~30%. The ability to reach near theoretical strength and large plastic deformation has made these materials a serious contender for the above applications. The strength of these nanoscale materials are strongly derived from the interface structure compared to its bulk counterpart. The underlying strengthening mechanisms at this incoherent (large lattice parameter mismatch) interface of the face centered cubic (FCC) Cu, and body centered cubic (BCC) Nb structure, has been investigated using experimental techniques (ex/in-situ) and simulations (continuum/atomistic). Due to the recent technological advances in fabricating nanoscale, multi-material films of (few to tens) nanometers thick are possible, which are useful to interpret the interface dominated plasticity phenomenon of these materials.
In this study, pillar compression of nanoscale Cu/Nb single crystal multilayers with individual layer thickness (20 nm) is investigated. The samples were subjected to successive compression experiments with strain ramping up-to 35% respectively. Synchrotron X-ray micro-diffraction experiments, using a monochromatic beam of 10 keV energy were also performed on the pillars after each compression strain, providing us with insights on how plasticity in Cu and Nb nanolayers evolve. We observe a significant increase of peak broadening in both Cu and Nb layers up-to strains of ~4% followed by saturation of the X-ray ring width broadening until large plastic deformation of 35%. This observation indicates that the interfaces of the Cu/Nb nanolayers are very stable and effective in trapping and annihilating dislocation content during mechanical deformation. The nanolayer composite shows a maximum flow strength of ~1.6 GPa at ~24.2% compression strain. Further, these investigations affirm that, the Cu/Nb nanolayers can be deformed to large plastic strains without any onset of plastic instabilities. Beyond the plastic flow regime of these composites, understanding the failure also has attracted some interests recently, which is an additional point of interest.



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