Journal of Materials Research

Articles

Failure by simultaneous grain growth, strain localization, and interface debonding in metal films on polymer substrates

Nanshu Lu, Xi Wang, Zhigang Suo and Joost Vlassaka1 c1

a1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138

Abstract

In a previous paper, we have demonstrated that a microcrystalline copper film well bonded to a polymer substrate can be stretched beyond 50% without cracking. The film eventually fails through the coevolution of necking and debonding from the substrate. Here we report much lower strains to failure (approximately 10%) for polymer-supported nanocrystalline metal films, the microstructure of which is revealed to be unstable under mechanical loading. We find that strain localization and deformation-associated grain growth facilitate each other, resulting in an unstable deformation process. Film/substrate delamination can be found wherever strain localization occurs. Therefore, we propose that three concomitant mechanisms are responsible for the failure of a plastically deformable but microstructurally unstable thin metal film: strain localization at large grains, deformation-induced grain growth, and film debonding from the substrate.

(Received June 11 2008)

(Accepted September 23 2008)

Key Words:

  • Cu;
  • Ductility;
  • Thin film

Correspondence:

c1 Address all correspondence to this author. e-mail: vlassak@esag.harvard.edu

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