Co-existence of homogeneous flow and localized plastic deformation in tension of amorphous Ni-P films on ductile substrate

The room temperature mechanical behavior of amorphous Ni-P thin films deposited on Ni substrate under tension was systematically investigated. Due to the effect of substrate confinement, unexpected homogeneous plastic flow occurred in the film simultaneously with cracking or shear banding, which co-contributed to the plastic deformation. The film thickness gradually reduced with increasing tensile strain and the maximum reduction increased up to 69% in 2.6 mu m-thick film. Such a severe plastic deformation leads to significant structure change in the film where free volume annihilation dominates, evidently by almost 100% reduction in the total relaxation enthalpy in the deformed film, accompanied by the densification and hardening. The stress required for shear band and crack propagation in Ni-P film was analyzed on the basis of Griffith's criterion. A deformation map is proposed to account for coexistence of homogeneous flow and localized plastic deformation (shear banding or cracking), as well as the transition of deformation modes. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.