Control of the bath’s composition and temperature is crucial to the stability, energy consumption and material efficiency of the aluminium electrolysis process. The traditional approach involves periodic measurement of the bath’s composition with x-ray diffraction, as well as the bath’s temperature. The sampling and corrective measures applied to the cell can take 8–12 h. Since the relationship between the excess AlF3 in the bath and the temperature is difficult to manage, the electrolysis process involves a time lapse. With the integration of in situ measurements of the bath’s properties in the electrolysis cell, optimization of the primary aluminium reduction process was achieved. Increased measurement frequencies and the integration of in situ measurements into the electrolysis process reduced the instability of the process, resulting in energy savings and increased current efficiency of 96.4%.
COBISS.SI-ID: 1773663
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
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
This paper introduces improvements to an amplitude expansion of the phase-field-crystal model. An auxiliary field describing local grain rotation is introduced and used to enable the adaptive mesh to be coarsened in all grains, regardless of their orientation. Only a Cartesian representation of the amplitude equations is used.
COBISS.SI-ID: 1741663
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