Inverse size effects in un-notched and notched metallic glass thin films

The sample size effect on the deformation behaviors of metallic glasses (MGs) attracts a lot of interest. Here, a series of molecular dynamics simulations have been performed on un-notched and notched MG thin films to fully investigate the influence of sample thickness on their fracture strengths and failure mechanisms. With decreasing sample thickness, the failure strength of un-notched MG thin films decreases slightly and the failure mode changes from shear banding to homogeneous deformation. In contrast to this brittle-to-ductile transition observed in un-notched MG thin films, shear banding prevails for notched MG thin films regardless of sample thickness. Concurrently, a notch strengthening effect is observed in the notched MG thin films when the sample thickness falls close to the shear band (SB) thickness. This significant notch strengthening is due to the failure mode transition from homogeneous deformation in un-notched MGs to shear banding in notched MGs. Based on the energetic model, a theoretical analysis is proposed to rationalize the size effect on failure mechanism transitions of both un-notched and notched MG thin films. The present study offers an understanding of size effect on the un-notched and notched MG thin films, as well as useful guidelines for the design, testing, and engineering of MG for microelectromechanical applications.

Automated summary

The thickness of metallic glass thin films influences their fracture strength and failure mechanisms, with un-notched films transitioning from shear banding to homogeneous deformation as thickness decreases. In contrast, notched films consistently exhibit shear banding regardless of thickness, with a strengthening effect observed near the shear band thickness.