Grain boundary mediated plasticity: A blessing for the ductility of metallic thin films?

The limited ductility of metallic thin films (< 1%) poses a challenge to MEMS and flexible electronics applications. Here, we report on freestanding gold specimens with the remarkable ability to accommodate >= 10% plastic deformation while retaining a high strength. Using in situ nanomechanical testing in a transmission electron microscope, this exceptionally high ductility is traced back to the combination of an ultrathin thickness, a columnar microstructure and a (111) fiber texture. Under such conditions, the deformation is largely mediated by grain boundaries through grain boundary sliding and shear coupled grain boundary migration. Because these non-conventional mechanisms preserve the cross-sectional thickness of the specimens, necking is postponed and the samples can reach a high ductility. Since the mechanisms were evidenced at room temperature and under strain-rate conditions typical of most applications, the findings open up promising outlooks for developing ductile metallic films by microstructural engineering. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.

Automated summary

The limited ductility of metallic thin films poses a challenge for MEMS and flexible electronics applications, but high ductility can be achieved through a combination of ultra-thin thickness and specific microstructure. The primary mechanisms of ductility are grain boundary sliding and grain boundary migration, which delay necking and achieve high ductility. This study opens promising prospects for developing ductile metallic films through microstructural engineering.