200 nm Glide controlled creep D G is 115 kJ/mole 20% 20nm, 80% 200nm Climb controlled creep

1. FUNDAMENTAL UNDERSTANDING OF SUPERPLASTICITY IN NANOCRYSTALLINE METALS Amiya K. Mukherjee, University of California, Davis DMR 0240144 Bimodal Creep Mechanism Demonstrates Strengthening by Dislocation Frustration • 200 nm • Glide controlled creep • DG is 115 kJ/mole • 20% 20nm, 80% 200nm • Climb controlled creep • DG = 112kJ/mole • Small particles may store dislocations at opposite grain boundary, which has the potential to generate more dislocations. • Creep behavior of the sample shows direct evidence of the deformation mechanism being controlled by grain size distribution. • DG (activation energy for creep) is lower due to the location of the climb mechanism at the grain boundaries, where vacancies are abundant (see diagram). • Stress concentrations at adjacent • triple points lead to instability and failure at lower strains.

2. FUNDAMENTAL UNDERSTANDING OF SUPERPLASTICITY IN NANOCRYSTALLINE METALS Amiya K. Mukherjee, University of California, Davis, DMR 0240144 Outreach Training / Education: • Tammy Tamayo, Graduate Researcher at UCD, presented a talk on high-temperature superplastic properties of nanoscale metal at the MRS Spring Meeting in San Francisco, CA • Training includes: • TEM preparation of metallic specimens • General laboratory procedures: Operation of tensile machine/analysis of data • TEM operation: Registered user of UCD facility Postdoctoral Fellow Dr. Alla Sergueeva participated in the San Francisco Exploratorium’s Exhibition on Nanomaterials with emphasis in involving school children of the San Francisco Bay area and Northern California