Mechanical properties and thermal stability of nanocrystalline gold prepared by gas deposition method

Specimens of nanocrystalline Au with various grain sizes were prepared by the gas deposition method. Results of measurements of (1) Young's modulus by the nanoindentation method, (2) anelasticity, (3) grain size by SEM, STM and X-ray diffraction, (4) Vickers microhardness and (5) elastic limit by bending tests at R.T. and 77 K, and their behaviors during annealing were described. High mechanical strength almost as high as whiskers was found in as-deposited slate. Thermal stabilities of the grain size and mechanical strength were found to be higher for specimens with smaller initial grain size. For the specimens with grain size similar to 7 nm, no grain growth was observed up to annealing for 1 h at 770 K and a growth to twice of the initial size, even after 1070 K. Possible origins of this remarkable thermal stability were discussed.