KEYWORDS: Interfaces, Process modeling, Aluminum, Nanostructures, Data modeling, Solids, Adaptive optics, Crystallography, Aerospace engineering, Medicine
A review of theoretical models describing the strengthening and softening mechanisms in nanocrystalline materials under superplastic deformation is given. In the framework of these models, the strengthening occurs due to the effects of triple junctions of grain boundaries as obstacles for grain boundary sliding. The local migration of triple interface junctions (caused by grain boundary sliding) and the emission of lattice dislocations bring about softening of a nanocrystalline material. The flow stress is found as a function of the total plastic strain, and the results agree well with experimental data from nanocrystalline materials exhibiting superplasticity, reported in the literature.
The model for misoriented nano- and micro-crystalline inclusions in composite materials is proposed. Low-angle misorientation boundaries of inclusions are modeled by the arrays of rectangular dislocation loops. The energy of these boundaries for individual nanocrystallite and the cluster of nanocrystallites is determined in dependence of grain boundary misorientation.
KEYWORDS: Chemical species, Crystals, Solids, Data modeling, Thin films, Ion implantation, Solid state physics, Sapphire, Absorption, Chemical analysis
A theoretical model is suggested which describes the evolution of ensembles of point defects that give rise to solid state amorphization in initially crystalline films under irradiation. A kinetic equation for the density of point defects (vacancies and interstitial atoms) in irradiated solid films is proposed and solved with the assumption that the effect of ion implantation on the amorphization is negligible. In the framework of the proposed model, the temperature dependence of the dose-to-amorphization is calculated and compared with the corresponding experimental data [H. Abe et al, Nucl.Instrum. Meth. Phys.Res. B 127/128, 170 - 175 (1997)].
A theoretical model is proposed for the cohesive failure of multilayer composite systems. A general formula is derived which relates values of structural and geometrical parameters at which crack generation is energetically favorable in such composite systems. For one-layer film/substrate systems, the critical thickness is found above which the cohesive fracture of films is energetically favorable. Nucleation of an intermediate layer due to diffusion across a film/substrate interphase boundary is considered. It is shown that the generation and the growth of the diffusion layer may result in the spontaneous cracking of the film.
Relaxation of misfit stresses in heteroepitaxial systems occurs in many cases via the generation of either perfect or partial misfit dislocations (MDs). The formation of a row of parallel partial MDs has been theoretically described with the help of the simplified energetic approach do not taking into account interactions of MDs with the free surface and pre- existent misfit stresses as well as dislocation-dislocation interactions. However, these interactions are expected to essentially influence on behavior of partial MDs as it is the case with perfect ones. The main aim of this work is to theoretically examine the energetics of partial MDs located in the tips of V-shaped stacking faults with the above interactions being taken into account.
Conference Committee Involvement (1)
Nanotechnology
19 May 2003 | Maspalomas, Gran Canaria, Canary Islands, Spain
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