Peculiarities of mechanical behavior of nanocrystalline and noncrystalline materials

Yuly V. Milman 

Institute for Problems of Materials Science, 3, Krzhizhanovsky, Kyiv 03142, Ukraine

Abstract

The review of the mechanical behavior of nanocrystalline (NQ) and noncrystalline (amorphous (MG) and quasicrystalline (QC)) materials is given. Peculiarities of deformation mechanism for NQ materials are connected with the practically absence of dislocations in the body of grain (dislocations go out into the grain boundaries due to image forces) and realization of deformation in the grain boundaries.
In MG the dislocation mechanism of deformation is discussed for the range of nonhomogenious deformation. Strain hardening and localization of deformation in MG is considered. Yield stress σs of MG consists of thermal and very big athermal components. Thermal component is close to the thermal component of crystalline state. σs and hardness H of MG are very high, but NQ can have higher values of σs and H if d < 100 nm.
Plastic deformation of quasicrystals is of dislocation type, but Burgers vector of dislocations contains phason component, and dislocation movement is accompanied by the gradual destroying of quasicrystalline structure and in some cases by phase transition to crystalline state. The hardness of quasicrystals increases after annealing and decreases during deformation. QC with the nanosize grains (NQC) is the especial class of materials, because energy of dislocation connected with phason defects is proportional to d (not lnd as elastic energy of dislocations in crystals).
For this reason plasticity of NQC is more than in QC. Composite materials on the base of NQ, MG and QC can have high level of mechanical properties.

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Presentation: Invited oral at E-MRS Fall Meeting 2006, Plenary Session, by Yuly V. Milman
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-11 14:06
Revised:   2009-06-07 00:44
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