Examination of critical grain size of isotropic nanocrystalline iron through molecular dynamics analysis

ABSTRACT

The critical grain size for isotropic nanocrystalline pure iron was investigated utilizing Molecular Dynamics (MD). First, number of grains required for isotropic behaviour was determined utilizing statistically significant grain counts – alleviating challenges faced in simulation of nanocrystalline materials. The current investigation provides a thorough guideline for simulating isotropic nanocrystalline materials. Second, an investigation into the effect of strain rate was performed to demonstrate its effect on mechanical properties of pure, isotropic nanocrystalline iron. Next, the critical grain size of pure nanocrystalline iron was investigated, indicating the change from Hall-Petch to inverse Hall-Petch. It was shown that MD of an isotropic pure nanocrystalline iron structure possessed a clearly defined critical grain size through examination of flow stress and maximum stress. It was shown that neither elastic modulus nor Poisson’s ratio were viable indicators for a critical grain size, instead, both tended towards their macroscale equivalent. Alternatively, yield stress may be viable, but was not recommended due to varying definitions for what exactly constitutes the yield point. Lastly, an investigation into the microstructure was performed near the critical grain size and at the extremes of grain sizes investigated. This highlighted the microstructural behaviour within both Hall-Petch and inverse Hall-Petch regimes throughout straining.

KEYWORDS:

• Molecular dynamics
• nanocrystalline iron
• mechanical properties
• isotropy

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors are grateful for the financial support from Suncor Energy Incorporated and Natural Sciences and Engineering Research Council of Canada (NSERC).