Effect of pre‐existing dislocations on the strength of gold at very small scales
October 1-6, 2017
This work aims at understanding the effect of pre-existing dislocations on the strength of gold at very small scales. Previous studies have investigated this topic by correlating values of site-specific strength with average values of pre-strain or dislocation density of the parent bulk material. However, the mechanical response at the nano-scale is rather governed by the local microstructure of the small volumes being tested, which might not be representative of the average microstructure of the bulk material. Therefore, we propose a new method to correlate site-specific strength, as characterized by the hardness at the elastic-to-plastic transition, with the respective values of local deformation states, characterized non-destructively prior to nanoindentation using a new EBSD strain parameter derived from uncorrelated misorientation angle distributions. The analysis is performed on polycrystalline gold samples submitted to different degrees of bulk pre-straining. Consistent with other works, our results show that pre-existing dislocations decrease the strength of gold at the nano-scale; the Taylor relation is shown not to hold in this regime. We discuss this in view of a model proposed by Johnson and Ashby to predict the strength of a metal as a function of dislocation density, and a similar one applied to nanoindentation by Lilleodden and Nix. In addition, a conceptual model similar to that of Hall-Petch is used to analyze the results in the context of size effects in the strength of metals at small scales.
Paula O. Guglielmi, Markus Ziehmer, and Erica T. Lilleodden, "Effect of pre‐existing dislocations on the strength of gold at very small scales" in "Nanomechanical Testing in Materials Research and Development VI", Karsten Durst, Technical University of Darmstadt, Germany Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/nanomechtest_vi/23