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
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
A new test rig for thermal fatigue testing was used to inviestigate and characterise surface layer degradation of indefinite chill double pour (ICDP) cast iron hot work roller. We found that crack nucleation, crack propagation (growth), their linking and subsequent material spalling are related to the cementite and graphite particles characteristics. Revealed, were the appearance of internal cracks in cementite and graphite, propagation towards and from the test surface, cracks linking and material chipping. Based on observations, a better understanding of degradation mechanisms and their temperature related intensity was gained.
COBISS.SI-ID: 1690207
Hydrogen diffusion and trapping in ferrite is evaluated by quantum mechanically informed kinetic Monte Carlo simulations in defective microstructures. We find that the lattice diffusivity is attenuated by two to four orders of magnitude due to the presence of dislocations. We also find that pipe diffusivity is vanishingly small along screw dislocations and demonstrate that dislocations do not provide fast diffusion pathways for hydrogen as is sometimes supposed. We make contact between our simulations and the predictions of Oriani's theory of ‘effective diffusivity’, and find that local equilibrium is maintained between lattice and trap sites. We also find that the predicted effective diffusivity is in agreement with our simulated results in cases where the distribution of traps is spatially homogeneous; in the trapping of hydrogen by dislocations where this condition is not met, the Oriani effective diffusivity is in agreement with the simulations to within a factor of two.
COBISS.SI-ID: 1690463
Titanium alloys has gained acceptance in many media where its corrosion resistance and engineering properties have provided the corrosion and design engineer with a reliable and economic material. Titanium, like any other metal, is subject to corrosion in environments of air, oxygen, moisture, and so on. In this work, high-temperature stability of Ti and various Ti-alloys (by ASTM standard) was investigated. The best results showed that for Ti-Gr.5 alloy, the oxidation at 800 °C was 3.39% and at 900 °C 8.35%. For the comparison, commercial pure Ti-alloys Ti-Gr.2 and Ti-Gr.37 containing Al were used, whereas the oxidation resistance was much worse. The research is also very important for Slovenian industry, e.g. Akrapovič d.d.
COBISS.SI-ID: 1666399