Is diffusion creep the cause for the inverse Hall-Petch effect in nanocrystalline materials?
It has previously been demonstrated by means of molecular-dynamics (MD) simulation that for the very smallest grain sizes (typically below 20-30 nm), nanocrystalline fcc metals deform via grain-boundary diffusion creep, provided the applied stress is low enough to avoid microcracking and dislocation nucleation from the grain boundaries. Experimentally, however, the nature of the deformation process in this “inverse Hall-Petch” regime (in which the yield stress decreases with decreasing grain size) remains controversial. Here we illustrate by MD simulation that in the absence of grain growth a nanocrystalline model bcc metal, Mo, and a model metal oxide, UO2, also deform via diffusion creep. However, in the case of Mo both grain-boundary and lattice diffusion are observed to contribute to the creep rate; i.e., the deformation mechanism involves a combination of Coble and Nabarro-Herring creep. While our results on Mo and UO2 are still preliminary, they lend further support to the observation of diffusion creep previously documented in fcc metals and in covalently bonded Si.
- Research Organization:
- Idaho National Laboratory (INL)
- Sponsoring Organization:
- DOE - SC
- DOE Contract Number:
- AC07-99ID13727
- OSTI ID:
- 936869
- Report Number(s):
- INL/JOU-07-12316
- Journal Information:
- Materials Science and Engineering A, Journal Name: Materials Science and Engineering A Journal Issue: 1 - 2 Vol. 493
- Country of Publication:
- United States
- Language:
- English
Similar Records
ATOMISTIC SIMULATIONS OF DIFFUSIONAL CREEP IN A NANOCRYSTALLINE BODY-CENTERED CUBIC MATERIAL
Complications of diffusional creep at very small grain sizes