arXiv subjects

Dalibor Preisler

Publications and source records attributed to Dalibor Preisler.

4 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↗

arXiv2025

Microstructure and phase stability within the AlMoNbTiZr system: design tools and compositional boundaries for a high-entropy alloy

This study explores Ti-containing complex concentrated alloys (CCAs) within the AlMoNbTiZr system, focusing on compositions located in regions of the Bo-Md diagram characterized by low bond order (Bo) and d-orbital energy level (Md). Four alloys were designed near the line predicting stress-induced martensite formation in conventional Ti alloys, then cast, annealed at 1200°C, and water quenched. Their microstructures and phases were analyzed and compared against phase prediction tools commonly applied to high-entropy alloys (HEAs), namely empirical parameters and CALPHAD simulations. Results highlight the strong influence of chemical affinity, particularly the roles of Al, Mo, and Zr concentrations, on solid-solution stability. A maximum Al content of 10 at% was identified as the threshold for achieving a single-phase microstructure, observed in the 10Al15Mo10Nb35Ti30Zr alloy. This alloy exhibited a bcc/b2 structure with high compressive strength (above 1300 MPa), low Young's modulus (28 GPa), and limited strain (<6%), but lacked the transformation-induced strengthening mechanisms expected for Ti alloys with comparable Bo-Md values.

cond-mat.mtrl-sci↗

arXiv2025

Stress-induced phase transformations in Ti-15Mo alloy at elevated temperature

Controlled mechanical loading was applied to Ti-15Mo alloy during annealing at 550 $^\circ$C. Massive formation of the $ω_{\textrm{iso}}$ phase from the parent $β$-phase occurred during annealing at 550 $^\circ$C without external stress or with stress well below the yield stress. Moreover, a massive $α$ phase precipitation takes place under simultaneous annealing and plastic deformation. Plastic deformation plays a key role in $β\rightarrowα$ transformation and achieving refined $α+β$ type microstructure resulted in improved mechanical properties. Studying phase transformations during plastic deformation is critical for understanding and optimizing thermomechanical processing of metastable $β$-Ti alloys.

cond-mat.mtrl-sci↗

arXiv2024

Heterogeneous dynamic restoration of Ti-15Mo alloy during hot compression

Near-beta titanium alloys have shown low Young's modulus and good strength, making them excellent implant candidates. However, their processing using thermomechanical routes in single phase beta region results in heterogeneous microstructures due to high content alloying elements and consequent slow diffusion-controlled processes such as dynamic recovery. This study investigates the deformation behaviour of a Ti-15Mo alloy through hot compression experiments using a Gleeble 3800 device in the single beta domain at strain rates from 0.01 s-1 to 10 s-1, reaching final strains of 0.50 and 0.85 followed by immediate water quench. The findings show that the material presents a low strain rate sensitivity. The flow curves show significant strain hardening before reaching a steady-state regime, particularly at high strain rates. The strain hardening exponent calculations support the effect of molybdenum on retarding softening mechanisms such as dynamic recovery. Electron backscatter diffraction (EBSD) measurements of deformed samples revealed that dynamic recovery is the primary restoration mechanism, with continuous and geometric dynamic recrystallisation evidence. Due to the slow restoration process, we observe the subgrain formation for different deformation parameters. Therefore, we introduced an EBSD-based method to quantify dynamic recovery and subgrain size. We concluded that dynamic recovery and dynamic recrystallisation decrease as the strain rate increases with minimal variation at higher strain rates.

cond-mat.mtrl-sci↗