O. Hunderi

On the Zener drag

Abstract The interaction between particles and a grain boundary has been studied. Both the relatively simple problem of the interaction between a single particle and a grain boundary, and the much more complicated problem of deriving a restraining force from the many particles on a grain boundary have been considered. The conclusion is that the estimate due to Zener and Smith—now nearly 40 years old—is still of good value. The effects of particle shape and distribution on the Zener drag have also been included, and it is demonstrated that such effects may strongly influence recrystallization and grain growth behaviour.

Computer simulation of primary recrystallisation microstructures: The effects of nucleation and growth kinetics

Abstract We have studied the influence of nucleation and growth kinetics on the size distribution of grain section areas after primary recrystallisation. The microstructures were generated by computer simulation of the recrystallisation process. In addition to the conventional site saturation and Johnson-Mehl nucleation kinetics, we have also studied the influence of increasing and decreasing nucleation rates and a decreasing growth rate on the size distribution. The resulting distributions are compared to an experimental distribution obtained from an AlFeSi-alloy.

A comment on the Lifshitz-Slyozov-Wagner (L-S-W) theory of particle coarsening

La theorie LSW montre que la taille moyenne a la puissance 3 des particules augmente lineairement avec le temps, avec une pente unique apres la distribution quasi stationnaire. Commentaire portant sur la theorie LSW et revue des methodes mathematiques de resolution des equations differentielles conduisant a la theorie

Modelling grain growth in two dimensions

Abstract Three models for grain growth in two dimensions are developed and compared. The first one considers only one grain growing in a smeared-out environment of all the other grains. The two other models also take into account the equilibrium at the nodes with one or two nearest neighbouring grains. It is concluded that the quasistationary grain size distributions derived from these models are much more peaked than is observed experimentally. Finally it is pointed out that equilibrium at the nodes may introduce grains of variable sizes but with zero growth rate. It is shown that this reduces the rate of growth of grains with sizes around the mean size compared with the rate of growth given by Hillert. The corresponding quasistationary distribution has a tail towards larger grain sizes.

On the thermal oxidation kinetics of two metallic glasses

Abstract The oxidation kinetics of two metallic glasses have been studied by ellipsometry and Auger Electron spectroscopy. The presence of chromium in Fe-based alloys has a marked influence on the corrosion film formed and on the kinetics of film formation. The chromium-free alloy shows piecemeal parabolic oxide growth; this is transformed into a logarithmic growth law for the chromium concentration studied. The influence of moisture on the kinetics of film formation has also been studied.

The optical properties of thin films and superlattices

The rapidly growing interest in quantum well and superlattice physics has led to a strong increase in research in the physics of thin films, multilayer structures and the interface between solid media. In this paper we discuss the relationship between the structure, composition and design of a multilayer system or superlattice and the macroscopic dielectric response of the composite structure. Particular emphasis is given to interphase phenomena as these may be strongly enhanced in a multilayer structure.

In situ measurement of pitted area by diffuse light scattering

In studies of pitting corrosion, there is often a need for monitoring the size of growing pits in situ as well as the need for a rapid assessment of the extent of pitting damage ex situ on a large number of test specimens. The well-known method of determining surface roughness by diffuse light scattering has been adapted to satisfy both needs. In situ measurements with aluminium alloys immersed in NaCl solutions indicate that early stages of pit propagation can be monitored accurately. Furthermore, measurements on pre-pitted aluminium show that the technique is suitable for rapid, quantitative determinations of a pitted area up to a fraction of 40%.

Optical properties of superconducting Y Ba Cu O

The dielectric function of YBa2Cu3O7 has been measured by spectroscopic ellipsometry in the spectral range 0.5–4.0 eV. Spectra were obtained at room temperature (300 K) and 80 K. The spectra at the two temperatures were nearly identical. The imaginary part of the dielectric function e2 has been compared with recent band structure calculations of YBa2Cu3O7. These band structure calculations were made for two differnt positions of oxygen in the unit cell. The experimental spectra show marked features associated with interband transitions and these features can be associated with transitions at high symmetry points and symmetry lines in the Brillouin zone. Assignments of interband features in the experimental spectra are somewhat better for one of the oxygen positions than for the other.

Diffuse light scattering: A way to study pitting corrosion in situ

Abstract A new method for the study of pitting corrosion allows pit evolution to be followed in situ in aqueous media. It has been used to compare pitting corrosion in aluminium alloys of various copper contents.

Transfer matrix formalism applied to above barrier energy states in strained multiple quantum wells

We have used the effective mass approximation in a transfer matrix formalism to describe both confined and unconfined (above barrier) states in strained InGaAs/GaAs multiple quantum well (MQW) structures. We deduce the transfer matrices for a pseudomorphic MQW structure from the envelope wavefunction boundary conditions, modified to account for the discontinuities in the lattice constant. In the calculations we also take into account the finite width of the cap-layer, and the finite height of the vacuum potential. The potential profiles of the InGaAs/GaAs MQWs are derived using the calculated positions of the band-edges, taken from the model-solid theory. Photoluminescence excitation (PLE) spectroscopy has been performed on a series of InGaAs/GaAs MQWs (4-6 periods) at 11 K. We observed excitonic peaks at energies both below and above the GaAs free exciton. The values of the calculated transition energies are in good agreement with the experimental peaks.