Date: Tuesday, November 10, 2009 4:30 PM
Location: 366 Hollister
Recent experiments on nanoscale materials, including nanowires, nanopillars, nanoparticles, thin films and nanocrystals, have revealed a host of “ultra-strength” phenomena, defined by sample-wide stresses rising up to a significant fraction (>1/10th) of the ideal strength - the highest achievable strength of a defect-free crystal. While conventional materials deform or fracture at sample-wide stresses far below the ideal strength, rapid development of nanotechnology has brought about needs to understand ultra-strength behavior, which not only have to do with the forming and shape stabilities of a material component, but also its functional properties. Reaching ultra-strength enables “elastic strain engineering”, where by controlling the local elastic strain one achieves desired electronic, magnetic, optical, catalytic etc. properties in the component, and greatly expands the materials selection space. Distinctive deformation mechanisms in ultra-strength materials will be reviewed, where the competition between displacive and diffusive processes is highlighted. The critical role of the activation volume is explained, as well as the size, temperature, and strain rate dependence of ultra strength. Important unresolved issues are identified.
S. Suresh and J. Li, Nature 456 (2008) 716
T. Zhu, J. Li, S. Ogata and S. Yip, MRS Bulletin 34 (2009) 167
