A significant decrease in hydrogen absorption in the presence of grain boundary carbides compared to the carbide-free microstructure in the Ni-based HR6W alloy was measured by thermal desorption analysis (TDA). This novel observation is at odds with numerous existing reports – precipitate-rich microstructures generally absorb more hydrogen due to trapping effects. This discrepancy can only be explained by grain boundary diffusion which is known to be fast in Ni-based alloys. It is proposed that grain boundary diffusion is hindered by carbides, resulting in decreased hydrogen absorption. Further experimental evidence corroborates the hypothesis. In addition, a diffusion model was developed to quantify the experimental results, incorporating trapping, grain boundary diffusion and temperature effects. It was successfully applied to the reported TDA data as well as additional diffusion data from the literature. A parametric analysis showed that hydrogen absorption scales strongly with grain size and grain boundary diffusivity while grain boundary segregation energy has a much lower impact. The results of the study point at grain boundary precipitation as a possible means of hydrogen embrittlement mitigation in Ni alloys and austenitic stainless steels.
COBISS.SI-ID: 1762143
In silico numerical experiments are a valuable tool for non-invasive research of the influences of tissue properties, electrode placement and electric pulse delivery scenarios in the process of electroporation. The work described in this article was aimed at introducing time dependent effects into a finite element model developed specifically for electroporation. Reference measurements were made ex vivo on beef liver samples and experimental data were used both as an initial condition for simulation (applied pulse voltage) and as a reference value for numerical model calibration (measured pulse current). The developed numerical model is able to predict the time evolution of an electric pulse current within a 5% error over a broad range of applied pulse voltages, pulse durations and pulse repetition frequencies. Given the good agreement of the current flowing between the electrodes, we are confident that the results of our numerical model can be used both for detailed in silico research of electroporation mechanisms (giving researchers insight into time domain effects) and better treatment planning algorithms, which predict the outcome of treatment based on both spatial and temporal distributions of applied electric pulses.
COBISS.SI-ID: 11363668
The effect of Ce addition on the AA A360 (Al–10%Si–0.5%Mg) alloy was investigated using equilibrium thermodynamic calculation, thermal analysis, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The purpose is to study the variations that occur during solidification and precipitation with different Ce additions, as well as their effect on the mechanical properties. The results show that the Ce addition decreases the eutectic (?Al + Mg2Si) temperature. The solidus temperature also decreases with the increasing Ce addition. The precipitation enthalpy determined using DSC decreases with the Ce addition, while precipitation takes place more rapidly and intensively, indicating increased reaction kinetics. The mechanical properties like hardness and tensile strength also increase with the Ce addition. The phase that contributed to the hardness of the investigated alloy was composed of Al, Ce, Mg and Si.
COBISS.SI-ID: 1133407
This paper describes the means by which hot deformability may be improved for one of the most challenging materials with respect to hot deformability. Deformation conditions for improved crushing of initial eutectic carbides networks during the first stages of hot working are identified. Apparent activation energies for hot working in two temperature ranges are determined. The microstructure and respective carbides are characterised by field emission scanning electron microscope, optical microscopy, X-ray diffraction and the results compared to equilibrium thermodynamic modeling.
COBISS.SI-ID: 1349982
Thermal fatigue resistance of a high Cr hot work roller steel is evaluated at 500, 600 and 700?°C. Surface layer degradation was investigated and characterised after a finite number of thermal cycles. Degradation mechanisms of the cooled surface layer in relation to the size, shape, orientation, distribution of carbides and crack oxidation progress were elucidated. Complex phenomena of crack growth is discussed where internal cracks nucleate due to stress at crack tip and oxidation along carbides follows from crack tail. Quantitative evaluation of cracks shows increased crack length with increasing temperature and number of thermal cycles.
COBISS.SI-ID: 1773919
This research aimed to optimise the structure of the multifunctional water- and oil-repellent, antibacterial, and flame-retardant hybrid polysilsesquioxane coating to increase its washing fastness to cotton fibres. In the pre-treatment process, pre-prepared Stöber silica particles were applied to the fibres by a pad-dry-cure process followed by the in situ generation of a tetraethyl orthosilicate (TEOS)-based particle-containing polysiloxane layer. The results showed that the inclusion of T4 into the MC sol increased the washing fastness of the coating to a significantly greater extent than the inclusion of T, and the washing fastness even further it increased if silica particles were deposited on the fibres in the pre-treatment process. The structural optimisation of the coating also led to the improvement of the functional properties of the coating, which exhibited the “Lotus effect” and simultaneously demonstrated high antibacterial activity.
COBISS.SI-ID: 3354736
In this investigation we studied the relationships between the design of dies for aluminium hot extrusion, the contact pressures on the die's bearing surface, the length of the bearing surface, the quality of the nitrided layer and the service lifetimes of the dies. Obtained results explain important aspects for decreased service time of dies. It was found that increase of service times of dies is possible if initial wear is concentrated on central part of bearing surface length.From wear patterns and time of their occurrence contact pressure on bearing surfaces can be assessed.
COBISS.SI-ID: 1684575
In order to improve the hot workability of AISI D2 tool-steel ingots during several heats hot deformation process, laboratory hot-compression tests as well as industrial investigations of the carbides' behaviour were carried out. The conditions that led to the occurrence of undesired, oversized carbides in the matrix were estimated and explained. It was found that to high soaking temperature results in an increased size of carbides which decreases hot workability. The results of industrial investigations show that area fraction of carbides after the end of each deformation cycle remains almost constant, but their mean size more than double during deformations in several heats which implies that the final microstructure is not dependent primarily on the last soaking-deformation cycle but depends on entire processing history, i.e. hot workability over several hot-deformation cycles can change considerably from cycle to cycle.
COBISS.SI-ID: 1287775
The XFEM is a powerful method to handle strong discontinuities in a finite element environment, especially in the study of the final stages of material failure, modelling the propagation of cracks, suppressing the need of remeshing. Nevertheless, for some materials undergoing large strain processes without noticeable volume changes, the discretization technique employed must not only describe the material behaviour but also correctly address the incompressibility constraints. In order to develop a robust formulation for this type of problems, an approach based on the analyses of the underlying sub-space of incompressible deformations embedded in the XFEM approximation is used, in the context of both infinitesimal and finite strains. This study motivated the extension of the conventional formulations of B-bar and F-bar to include the XFEM enrichment functions, whose performance is evaluated through some numerical examples and compared with competing methods such as the enhanced strain formulation.
COBISS.SI-ID: 1198687
The aim was to determine the mechanisms of wear on roller cone bit materials according to the characteristics of the steel material of the roller cone bit and the characteristics of the rock material. The results of our analysis present the mechanisms that result in the wear of the roller cone bit material under the given conditions of the rock material and the drilling regime. The results of the discovered wear mechanism can be used to improve the material of the roller cone bits in order to achieve a longer operating life and decrease the related costs of drilling.
COBISS.SI-ID: 1762399