Defect and Diffusion Forum Vol. 264

Abstract: We considered a polycrystalline cylindrical nanowire with bamboo microstructure strained uniaxially by an external load. Our molecular dynamic computer simulations demonstrated that grain boundary grooving plays an important role in determining the morphological stability of nanowires. Also, an exceptionally high yield stress of nanowires emphasizes the importance of diffusion in their plastic deformation under applied load. We formulated a phenomenological diffusion-based model describing morphological stability and diffusion-controlled deformation behaviour of polycrystalline nanowires. The kinetics of the shape changes was calculated numerically.

Abstract: The models of liquid –metal embrittlement (LME) which explore the concept of fast stress/strain induced liquid phase diffusion as the major factor responsible for acceleration of subcritical cracks are overviewed and refined. The models are used for further analysis of several focus issues in the LME kinetics.

Abstract: Annealing environment effect on the phase formation in Ni(10 nm)/C(2 nm)/Si(001) thin film system produced by sequential sputtering of C and Ni targets without vacuum breaking was under investigation. The specimens were annealed 30 s in vacuum of 1.3·10-4 Pa and in nitrogen flow in the temperature range of 450 - 1000°C. The temperature stimulated solid-state reactions that occur as the result of interdiffusion processes between layers of the thin film system under investigations were examined by X-ray - and electron diffractions, resistivity measurements and Rutherford backscattering. It was established that an annealing environment has a strong impact on the development of the solid-state reactions in Ni(10 nm)/C(2 nm)/Si(001) thin film system.

Abstract: Influence of an annealing environment and film thickness on the phase formation in the Ti(30 nm)/Si(100), [(Ti+Si) 200 nm]/Si(100) thin film systems produced by magnetron sputtering and the Ti(200 nm)/Si(100) thin film system produced by electron-beam sputtering were investigated by X-ray and electron diffraction, Auger electron spectroscopy (AES), secondary ion mass-spectrometry (SIMS) and resistivity measurements. Solid-state reactions in the thin film systems under investigation were caused by diffusion processes during annealing in the different gas environments: under vacuum of 10-4 - 10-7 Pa, flow of nitrogen and hydrogen. It is shown that the decrease of Ti layer thickness from 200 to 30 nm in the Ti/Si(100) film system causes the increase of the transition temperature of the metastable C49 TiSi2 phase to the stable C54 TiSi2 phase up to 1070 K at vacuum annealing. During annealing in the nitrogen flow of the Ti(30 nm)/Si(100) thin film system the C49 TiSi2 is the first crystal phase which is formed at 870 K. For annealings of the [(Ti+Si) 200 nm]/Si(100) thin film system by impulse heating method or for furnace annealings in inert gas atmosphere of N2, Ar, H or higher vacuum (10-5 Pa) the crystallization process has two stages: the first metastable C49 TiSi2 phase is formed at 870 K and then at higher temperatures it is transformed to the stable C54 TiSi2 phase.

Abstract: Experiments of niobium diffusion at infinite dilution and Nb reaction-diffusion in pure iron and in ferrites with different amounts of carbon were performed, for comparison, in order to understand the influence of carbon on the diffusion process in the Nb-Fe system. A proportional decrease of the diffusion coefficient with the increasing amount of carbon was found. This effect seems to be stronger than in the self-diffusion analyzing the literature; moreover SIMS measurements in niobium- implanted samples show a redistribution of carbon during the first steps of the diffusion process. For those reasons, a stronger effect of carbon-niobium interaction over the carbon-vacancy interaction seems to be responsible for the decrease in the diffusion coefficient.

Abstract: Thirty years ago, Lagües and Domange [1] studied surface segregation kinetics and proposed a method by which it is possible to determine the equilibrium surface segregation isotherm from one measurement, supposing that the local equilibrium hypothesis (LEH) is obeyed. This method has been using widely in the literature (e.g. [2-4]) since its born. It was used e.g. to study of dissolution of thin films into different substrates. In this case additionally it was assumed that the kinetics can be described by the classical Fick I equation (hybrid method). In this paper, using computer simulations, we investigate that under which conditions the LEH is obeyed during the dissolution of a thin film. Moreover, we show that even when the LEH is fulfilled the proposed ‘hybrid’ method cannot be always applied. We make also some considerations on the effect of stress fields developed by the redistribution of the solute elements during the segregation kinetics.