Abstract: In this work we show our result of in-situ nitrocarburizing and nitriding treatments AISI316L specimens. Part of the samples have been depassivated ex-situ and coated with a Ni layer, while other specimens received in-situ depassivation. Processing was carried out in a custom built reaction chamber attached to a Bruker D8 Advance diffractometer. We monitored the 111 peak of both the base material and expanded austenite. From the shrinkage of the base material peak the total thickness of the expanded austenite can be determined. Applying both N and C resulted in a more than 10 times faster growth of the expanded austenite than with N only. The growth is thermally activated. The activation energy for nitrocarburizing is 164 kJ/mol. This is in agreement with the activation energy of the diffusion of interstitials. Detailed analysis of the expanded austenite peak allowed the derivation of a “master curve” for the composition depth profile. This suggest that two interacting process controls the evolution. The width of the reaction zone is limited by the diffusion at low concentration side. The total concentration is determined by the reaction at the interface.
Abstract: The model explaining the occurrence of the electron concentration step front during oxidation of nitrogen-doped TiO2-δ thin films is presented. This model is based on ambipolar chemical diffusion coefficient analysis, for which immobile and uniformly distributed nitrogen component is assumed. The diffusion species and oxygen activity (pressure) profiles are obtained by numerical and approximate analytical simulation of the chemical diffusion. The profiles indicate the presence of two separate singularities: the electron concentration step front, and the electron-hole recombination reaction front. The electron concentration step front relates to the singularity of the ambipolar diffusion of three types of charged species with essentially different diffusion coefficients.
Abstract: This is a theoretical study of species profiles during the oxygen chemical diffusion in an acceptor doped oxide crystal driven by large changes in the ambient oxygen partial pressure. The oxide crystal containing three species: mobile oxygen vacancy, mobile electron, immobile dopant ion, is considered. Our analysis is based on the expression of the chemical diffusion coefficient obtained in the framework of the concept of conservative ensembles (Maier J., 1993). It is shown that the dependence of chemical diffusion coefficient on ambient oxygen partial pressure in double-logarithmic coordinates is divided into distinct intervals. For each pressure interval the chemical diffusion equation is reduced to the diffusion equation with a diffusion coefficient which exhibits a power dependence on concentration. First, we analyzed the chemical diffusion under pressure inside each interval. As a result two singularities on the species diffusion profiles can be found: an internal reaction diffusion front, and an ambipolar diffusion front. This ambipolar diffusion front is characterized by a step of the electron concentration, moving inside a specimen. Afterwards, we consider a crystal in which the range of partial pressure spans all considered pressure intervals.
Abstract: The paper reports on the results of two-stage-experiments of low-temperature ion nitriding of the Ti-6Al-4V titanium alloy in a non-self-sustained high-current arc discharge and in a glow discharge under various conditions. The diffusion of nitrogen into the interior of the material was determined by the thickness of the layer being modified. It was established that the depth of the nitrided layer greatly depends on temperature, composition of the working medium, as well as on process duration. When treated in non-self-sustained high-current arc discharge, the depth of the nitrided layer increases from 4 to 17 μm, and in the glowing discharge the depth increases from 9 to 13 μm. The nitriding temperature affects the sign and magnitude of the residual stresses.
Abstract: The paper discusses the influence of ultrafine-grained structure of martensitic and austenitic steels on diffusion processes at low-temperature ion nitriding. The microstructure of ultrafine-grained steels was analysed before and after nitriding. Depth distributions of microhardness are given depending on the class and structure of steels. The study proves that ultrafine-grained structure of steels obtained by high pressure deformation by torsion allows an increased growth rate of the diffusion layer at nitriding.
Abstract: Impact of a constant magnetic field on decomposition of supersaturated solid solution is investigated for the system Cu-Be-Ni. A technical bronze Cu-1.9Be-0.3Ni (in wt.%) was water-quenched after holding at 800°C (0.5 h) and subsequently heat treated at 325°C, 350°C and 400°C for 1 hour without and with application of a constant magnetic field of 0.7 T. The annealing in magnetic field is found to influence significantly the precipitation characteristics in diamagnetic Cu-based alloy, especially at 325°C. The nucleation barriers for discontinuous precipitation at grain boundaries are decreased, while the growth rates seem to be decreased, too, in magnetic field. A possible mechanism of the magnetic effect on discontinuous precipitation in the Cu-based is discussed.
Abstract: A brief review of the magnetoplastic effect during aging of quenched aluminum, copper, titanium and magnesium alloys in constant magnetic field is presented. We report the effect of thermomagnetic treatment on the composition and microstructure of the studied alloys, and on their mechanical properties, which constitutes the core of the magnetoplastic effect.
Abstract: The impact of a pulsed magnetic field on Sn diffusion in α-Fe is investigated within the magnetic field intensity range of 79.6–398.0 kА/m and the frequency range of 1–21 Hz at 730, 740, and 750 °С. The solute diffusion coefficients were measured by X-ray diffraction analysis. The pulsed magnetic field was found to influence significantly the diffusion coefficients of Sn in α-Fe. A resonant maximum of the bulk diffusion coefficient is observed at the frequency of 13 Hz and the magnetic field intensity of 398.0 kА/m. Possible mechanisms of the established magneto-diffusion coupling are discussed.
Abstract: 3D-printing or additive manufacturing (AM) is a group of novel intensively developed production processes, through which a "printed" object is fabricated layer-by-layer in a desired intricate geometrical shape with following joining it into a monolithic bulk by means of electron beam (EB) or laser beam (LB) melting. The present study is concentrated on the production of simple-shaped (cylindrical) Ti-6Al-4V alloy samples by Electron Beam Melting (EBM). During the rapid cooling of as-printed material's layer, martensitic structure is formed while suppressing of material's diffusivity. Effect of heat transfer conditions on the microstructure and properties obtained has been investigated. Heat transfer modelling and simulation was done utilizing the ABAQUS software package. The microstructure of the obtained material has been characterized by means of SEM and XRD. Microhardness have been also determined and correlated with the simulation results.