In Situ FESEM Observation/EBSD Analysis of Creep Crack Propagation in Freestanding Gold Nano-Films

Abstract

To clarify the mechanisms of creep crack propagation in metallic thin films (nano-films), in situ FESEM observation/EBSD analysis of creep crack propagation in freestanding gold films with approximately 340 nm in thickness was conducted. We developed an in situ FESEM/EBSD creep testing machine which was able to precisely apply a constant tensile load (stress) to a freestanding film specimen under FESEM observation at tilting angles of up to 70 degrees and EBSD analysis. Creep crack was propagated by repeating the processes of (i) necking-like creep deformation in the thickness direction ahead of the crack tip, (ii) void nucleation at the bottom of the necking-like creep deformation region, and (iii) creep crack propagation through coalescence of voids and/or main crack. Void nucleation and growth occurred along the grain boundaries. Creep deformation and subsequent fracture occurred in a grain between voids or between main crack and a void, resulting in coalescences of voids and/or main crack.