Thermomechanical processing of metals at the nanoscale
Eugen Rabkin, Technion - Israel Institute of Technology, Haifa, Israel
We employed a solid state dewetting technique to produce arrays of single crystalline metal particles (Au, Fe, Ni, Mo) of sub-micrometer dimensions on sapphire substrates. The particles were plastically deformed employing several complementary techniques: atomic force microscopy (AFM) – based nanoindentation with a sharp diamond tip, high-frequency tapping by the sharp diamond tip (nano-forging), and depth-sensing nanoindentation with a flat diamond punch [1-2]. All particles exhibited exceptionally high strength exceeding that of corresponding bulk metals by more than an order of magnitude. In particular, the maximum compressive strength of 34 GPa was measured for Ni particles, which is higher than the strength of any other metal or alloy, technical ceramics or silicon nitride, and approaches the tensile strength (lower bound) of carbon nanotubes . Heat treatments of the deformed particles demonstrated that they arrive to the equilibrium crystal shape much faster than their pristine counterparts. We employed this technique for determining the equilibrium crystal shape of -Fe, and the energy of iron-sapphire interface. We found a window of annealing parameters of the deformed Au particles in which they demonstrated self-healing and shape memory effects: the indented non-equilibrium single crystalline particles returned to their initial faceted non-equilibrium shape after heat treatments at 600 °C . We discussed our findings in terms of dislocations nucleation – controlled plasticity, and accelerated diffusion along the surface ledges produced by plastic deformation. We augmented our experimental discoveries by molecular dynamics simulations that closely mimic the experimental conditions.
Session W3: Wednesday, 27 June 2018
End: 03:00 p.m.