The effects of composition and microstructure on compressive strength of Ag-Au nanoparticles

Hemispherical nanoparticles of Ag-33 at.% Au and Ag-60 at.% Au alloys were fabricated by solid state dewetting of Ag-Au bilayers deposited on a sapphire substrate. The in-situ microcompression tests of the particles in the scanning electron microscope have revealed the plastic deformation behavior typical of plasticity which is controlled by the nucleation of new dislocations: high elastic strain reaching about 5% of the particle diameter, followed by a catastrophic particle collapse. The modulus-normalized average contact pressure at the onset of plasticity calculated employing the isotropic Hertz model was concentration-independent for pure Ag and two studied alloys. The atomistic molecular dynamics simulations of shear and compressive deformation of bulk Ag-Au alloys revealed a weak solid solution hardening effect for dislocation nucleation stress and its absence for the nucleation strain. The particles strength and critical strain obtained in simulations were in excellent quantitative agreement with the experimental results. The lack of solid solution hardening or weakening effects in the Ag-Au has been discussed in terms of small atomic size mismatch between Ag and Au. Finally, the effect of the twin boundaries observed in the Ag-Au particles on their strength was discussed.