Papers by Author: Vĕra Rothová

Abstract: In the temperature range 600–1000 °C, the effect of material purity on self-diffusion along grain boundaries has been studied in both the pure (Puratronic 99.9945%) and the technical (99.5%) nickel. The penetration profiles were measured by the serial sectioning method using the 63Ni radiotracer. The extensive electron backscatter diffraction (EBSD) analysis was performed on the same samples in order to reveal possible differences in microstructure induced by the impurity content. The obtained microstructure characteristics were further interpreted in terms of the coincidence site lattice (CSL) model.

Abstract: Grain boundary self-diffusion in both the cast and the cold-rolled Puratronic 4N5 nickel was studied in the temperature range from 600 °C to 1000 °C. The experiments were carried out with the samples pre-annealed at 1100 °C in comparison to the samples pre-annealed at intended individual diffusion temperatures. The relative grain orientation was analyzed on the same samples by means of electron backscatter diffraction (EBSD) and grain boundaries (GBs) were characterized in terms of the coincidence site lattice (CSL) model. Considering the non-linear Arrhenius temperature dependencies obtained for most specimens by using conventional method of profile evaluation in the B-type kinetics and the appearance of two high-diffusivity paths in diffusion profiles measured, a more suitable BB-type and AB-type diffusion models were applied for data evaluation.

Abstract: In this paper, four examples from the literature are introduced in which the presence of high density of twin boundaries could explain an anomalous diffusion behavior. (i) In the case of the grain boundary (GB) self-diffusion in nickel, leakage from the random GBs to considerably high fraction of deformation and/or annealing twins in the samples studied can be a reason for the diverse literature values of activation enthalpy. The diffusion model including participation of two types of GBs is essential for data evaluation. (ii) Segregation of Ge atoms with negligible solubility to twin boundaries and diffusion in both type A and type AB transition regime can clarify the unusual 71Ge diffusion in the Mg alloys. (iii) Anomalous diffusion of gold in polycrystalline silicon presented in the literature was discussed here. Because profiles corresponding to type AB transition regime were detected, transition from type B to type A diffusion regime could be an alternative explanation of the anomaly. (iv) Effective diffusion of the 63Ni tracer in the presence of unidirectional defects in single-crystalline β-tin might be a simple reason for the uncommon features published earlier: low activation enthalpy, high diffusion anisotropy and values of the extrapolated solid-state Ni diffusion coefficients above those in the Sn liquid phase.