arXiv subjects

Kristián Šalata

Publications and source records attributed to Kristián Šalata.

2 recordsLinked to original sources

arXiv2026

The effect of Nb and O on the martensitic transformation in the Ti-Nb-O alloys

This study examines the influence of niobium and oxygen on phase stability, crystal structure, and martensitic transformation pathways in Ti-Nb-O alloys. A series of Ti-(8-28)Nb-(0-3)O (at.%) alloys were prepared and solution-treated in the $β$-phase field. Microstructure and crystallography were characterized by X-ray diffraction, electron microscopy, and reciprocal-space mapping. A 2D-XRD orientation simulation approach was applied to distinguish all 12 crystallographically equivalent $α"$ martensitic variants originating from a single prior $β$ grain, enabling detailed diffraction analysis. This method further allowed quantitative evaluation of the atomic shuffle parameter y, describing the $β\rightarrowα"$ transformation. The results demonstrate that Nb primarily governs $α"$ martensite evolution. Increasing Nb stabilizes the $β$ phase and shifts the $α"$ structure toward higher symmetry, as reflected by systematic changes in lattice parameters and increasing shuffle parameter y, indicating suppression of transformation toward the hexagonal $α'$ phase. Oxygen, in contrast, modifies transformation pathways. At lower Nb contents, it suppresses the $ω$ phase formation and promotes $β\rightarrowα"$ transformation, while at higher Nb levels it inhibits long-range martensitic transformation, resulting in retained $β$ or competing $ω$ phase. These effects are attributed to local lattice distortions induced by interstitial oxygen.

cond-mat.mtrl-sci↗

arXiv2024

Phase Composition of AlTiNbMoV, AlTiNbTaZr and AlTiNbMoCr Refractory Complex Concentrated Alloys: A Correlation of Predictions and Experiment

Designing complex concentrated alloys (CCA), also known as high entropy alloys (HEA), requires reliable and accessible thermodynamic predictions due to vast space of possible compositions. Numerous semiempirical parameters have been developed for phase predictions over the years. However, in this paper we show that none of these parameters is a robust indicator of phase content in various refractory CCA. CALPHAD proved to be a more powerful tool for phase predictions, however, the predictions face several limitations. AlTiNbMoV, AlTiNbTaZr and AlTiNbMoCr alloys were prepared using blended elemental powder metallurgy. Their phase and chemical composition were investigated by the means of scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Apart from the minor contamination phases (Al2O3 and Ti(C,N,O)), AlTiNbMoV and AlTiNbMoCr exhibited single-phase solid solution microstructure at the homogenization temperature of 1400 °C, while Al3Zr5 based intermetallics were present in the AlTiNbTaZr alloy. None of the simple semiempirical parameter was able to predict phase content correctly in all three alloys. Predictions by CALPHAD (TCHEA4 database) were able to predict the phases with limited accuracy only. Critical limitation of the TCHEA4 database is that only binary and ternary phase diagrams are assessed and some more complex phases cannot be predicted.

cond-mat.mtrl-sci↗