arXiv subjects

Kristína Bartha

Publications and source records attributed to Kristína Bartha.

3 recordsLinked to original sources

arXiv2026

Designing Homogeneous Ti-Nb-Fe-Sn $β$ Titanium Alloys by PBF-LB: A Pre-Alloyed Powder Blend Strategy

Metastable $β$ titanium alloys are attractive for biomedical and structural applications owing to their low elastic modulus, high specific strength, and excellent corrosion resistance. Laser powder bed fusion (PBF-LB) enables complex-shape production and controlled compositional variation through powder blending. However, processing elemental Ti-Nb blends often results in chemical heterogeneity from incomplete dissolution of Nb-rich particles and non-equilibrium phase formation. To address this, low-modulus Ti-Nb-Fe-Sn alloys were produced by PBF-LB using Ti-42Nb, Ti-20Nb-15Fe, and Ti-20Nb-20Sn master-alloy powders blended with commercially pure Ti. Ti-23Nb-3Fe-4Sn, Ti-26Nb-2Fe-4Sn, Ti-29Nb-1Fe-4Sn, and Ti-32Nb-4Sn were fabricated using an uncommonly large 70 $μ$m layer thickness with layer remelting, followed by heat treatment at 1000 $°$C for 2 h and water quenching. After heat treatment, all alloys exhibited low porosity, homogeneous chemical distribution, and single $β$-phase microstructures with predominantly equiaxed grains and weak crystallographic texture. Thermodynamic calculations indicated that solidification descriptors alone could not explain the non-monotonic grain-size evolution, which was attributed to inherited solidification structure, transient TiFe-like phase formation, Nb/Sn partitioning, and/or solute-drag-controlled $β$-grain growth. Hardness and yield strength decreased with decreasing Fe and increasing Nb contents, from 268 to 224 HV and 691 to 468 MPa, respectively. Young's modulus, determined by resonant ultrasound spectroscopy, ranged 63-81 GPa. These results demonstrate that pre-alloyed master-alloy blends combined with remelting and heat treatment provide an effective route for producing chemically homogeneous Ti-Nb-Fe-Sn $β$ alloys while revealing how small compositional changes govern grain-growth behavior and mechanical response.

cond-mat.mtrl-sci↗

arXiv2026

Phase Equilibria of the Al-Ti-Nb-Zr-Ta System

Phase equilibria in the Al-Ti-Nb-Zr-Ta refractory complex concentrated alloy system were investigated using a high throughput experimental approach. A pseudo-ternary section of the quinary compositional space was prepared by a honeycomb type powder metallurgy design, consolidated by spark plasma sintering and subsequently homogenized at 1400 °C for 168 h. Phase constitution and chemical partitioning were characterized by SEM/EDS, XRD, EBSD, and TEM, supported by a custom EDS phase clustering workflow. Equilibrium microstructures consisting primarily of BCC, B2, and secondary phases were identified across the sampled compositions, with nanoscale precipitates forming in Zr and Ta rich regions. Measured phase compositions were compared with CALPHAD predictions, revealing both agreements and systematic deviations linked to CALPHAD database limitations. The results provide new experimental insight into phase stability and microstructural trends in Al-Ti-Nb-Zr-Ta alloys and demonstrate the effectiveness of high throughput combinatorial approaches for mapping complex multicomponent systems.

cond-mat.mtrl-sci↗

arXiv2025

Phase transformations in metastable $β$ Zr15Nb alloy revealed by in-situ methods

This study examines the phase transitions occurring during linear heating of the Zr15Nb alloy through a comprehensive, multi-technique methodology comprising in-situ high-energy synchrotron X-ray diffraction (HEXRD), electrical resistance measurements, differential scanning calorimetry (DSC), and thermal expansion analysis, supplemented by ex-situ transmission electron microscopy (TEM). The findings reveal a complex sequence of phase transformations and corresponding structural changes over a broad temperature range (from room temperature up to 800 $°$C). Two distinct body-centered cubic (bcc) $β$ phases - $β_{Zr}$ and $β_{Nb}$ - with closely related lattice parameters are identified. At room temperature, the microstructure is characterized by a mixture of the metastable $β_{Zr}$ + $ω_{ath}$ phase. Upon heating, $β_{Zr}$ progressively decomposes, giving rise to the formation of $β_{Nb}$. TEM observation revealed the cuboidal shape of the $ω_{iso}$ particles resulting from the high lattice misfit between $β$ and $ω$ phase. The $ω$ solvus temperature is determined to be approximately 555 $°$C, as evidenced by in situ HEXRD and abrupt changes in the alloy's thermal and electrical properties. The growth of the $α$ phase occurs after the dissolution of the $ω$ phase, resulting in a pronounced increase in thermal expansion.

cond-mat.mtrl-sci↗