Papers by Keyword: Internal Nitridation

Abstract: Thermal cycling has been observed to cause a transition from superficial alumina formation to internal oxidation and nitridation, an effect that was shown to depend on the specimen thickness and geometry, which can be described by a spalling-probability model. Once protection by a dense and adherent alumina scale got lost, the internal-corrosion rate is determined by the diffusivity and solubility of nitrogen and oxygen in the alloy. These parameters seem to depend not only on the temperature and the alloy composition but also on the applied mechanical stress. Internal nitridation under a superimposed creep loading was found to follow a higher rate constant than under just isothermal exposure. This effect can probably be attributed to dislocation-pipe diffusion, a mechanism which has been claimed also to be relevant for outward solvent diffusion during internal corrosion, a phenomenon, which was observed as a stress-relief mechanism during various internal-reaction processes

Abstract: Specific phase transitions to the compound-like impurity nanosegregation structures at dislocations and grain boundaries in metals and their influence on diffusion-assisted processes are considered, mainly, on the basis of the thermodynamic analysis of the related experimental data. The following systems and aspects are in detail considered: (1) the hydride-like nanosegregation of hydrogen at dislocations and grain boundaries in palladium and their influence on the apparent characteristics of hydrogen solubility and diffusivity in palladium; (2) the physics of the anomalous characteristics of diffusion of Fe and other transition impurities in crystalline Al at elevated temperatures, the role of the compound-like nanosegregation (CLNS) of Fe and the others at dislocations and grain boundaries in Al, analysis of the Mössbauer and diffusion data on CLNS of Fe at grain boundaries and dislocations in Al; (3) some new physical aspects of internal oxidation and nitridation of metals (for Cu-0.3%Fe alloy/Cu2O surface layer, and for (Ni-5%Cr) alloy / N2 gas), the role of the compound-like impurity nanosegregation at dislocations and grain boundaries, study results on the deviations from the classical theories predictions and their interpretation. The possibility is considered of nanotechnology applications of the study results for creation of nanostructured metals with compound-like nanosegregation structures at grain boundaries, in order to obtain specific physical and mechanical properties of such a cellural-type nanocomposites. In particular, it can be complex hydride-like, carbide-like, nitride-like, carbide-nitride-like, oxide-like or intermetallide-like nanosegregation structures at grain boundaries of nanostructured metals.