Microstructural Heterogeneity and the Mechanical Behavior of Nanocrystalline Metals

In this study, we have demonstrated through experiments on nanoscale metal films how the interplay between microstructural heterogeneity and size in ultrafine grained and nanocrystalline metals leads to unusual mechanical behavior. In the first part of the study, we have shown that (a) nanocrystalline metals, unlike their coarse grained counterparts, recover a substantial fraction (50 to 100%) of their plastic deformation after unloading, and (b) ultrafine grained metal films show a pronounced Bauschinger effect even at high tensile stresses during unloading. Then, we have presented evidence from in situ transmission electron microscopy and x-ray diffraction experiments that strongly indicate that these unusual phenomena are a direct consequence of the coupling between the small size and heterogeneity of the microstructure. Based on the in situ experiments, we have proposed simple mechanistic models to interpret these phenomena. Finally, we have shown that in nanoscale metal films with a homogeneous microstructure Bauschinger effect is substantially reduced.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Rajagopalan, Jagannathan

Contributors dc:contributor

• Saif, M. Taher A.

• Applied Mechanics

Language dc:language

eng

Identifier

(MiAaPQ)AAI3363064

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/83932