arXiv subjects

Miloš Janeček

Publications and source records attributed to Miloš Janeček.

6 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

Avalanche-like Plasticity in Complex Concentrated Alloys: A Review Across Scales

Complex concentrated alloys (CCAs), including high- and medium-entropy alloys, deform in chemically heterogeneous energy landscapes where dislocation glide, solute aging, twinning, phase transformation and microstructural barriers may all contribute. This review discusses avalanche-like and serrated plasticity in CCAs across scales. The first part separates the relevant length scales and methods used to access them. At microscopic and mesoscopic scales, acoustic emission (AE) and microcompression studies reveal discrete dislocation avalanches and strain bursts that may be hidden in conventional macroscopic curves. At the specimen scale, local extensometry and digital image correlation (DIC) studies of the Portevin-Le Chatelier effect show how collective defect dynamics can organize into deformation bands and macroscopic stress serrations. Together, these approaches show that plastic flow may appear smooth only as an average response, while remaining intermittent at finer scales. The second part reviews direct CCA evidence, with emphasis on AE, stress-serration statistics, microplasticity, DIC, nanoindentation and small-scale deformation. A central conclusion is that serrated flow in CCAs should not be treated as a single phenomenon. Depending on chemistry, temperature, strain rate and microstructure, it may originate from dynamic strain aging, twinning, martensitic transformation, slip localization, or a combination of these mechanisms. Reported power-law-like distributions and exponents partly overlap with those known from simpler crystals and alloys, and the present evidence does not establish a distinct CCA-specific universality class. CCAs are therefore best viewed as tunable systems in which chemical disorder, short range order, phase stability and microstructure can modify the nucleation, arrest and synchronization of collective plastic events.

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↗

arXiv2025

Finite-strain constitutive model for shape memory alloys formulated in the logarithmic strain space

This work presents a finite-strain version of an established three-dimensional constitutive model for polycrystalline shape memory alloys (SMA) that is able to account for the large deformations and rotations that SMA components may undergo. The model is constructed by applying the logarithmic strain space approach to the original small-strain model, which was formulated within the Generalized Standard Materials framework and features a refined dissipation (rate) function. Additionally, the free energy function is augmented to be more versatile in capturing the transformation kinetics. The model is implemented into finite element software. To demonstrate the model performance and validate the implementation, material parameters are fitted to the experimental data of two SMA, and two computational simulations of SMA components are conducted. The applied approach is highly flexible from the perspective of the future incorporation of other phenomena, e.g., irreversibility associated with plasticity, into the model.

cond-mat.mtrl-sci↗

arXiv2018

Ordered array of $ω$ particles in $β$-Ti matrix studied by small-angle X-ray scattering

Nanosized particles of $ω$ phase in a $β$-Ti alloy were investigated by small-angle X-ray scattering using synchrotron radiation. We demonstrated that the particles are spontaneously weakly ordered in a three-dimensional cubic array along the $\langle 100\rangle$-directions in the $β$-Ti matrix. The small-angle scattering data fit well to a three-dimensional short-range-order model; from the fit we determined the evolution of the mean particle size and mean distance between particles during ageing. The self-ordering of the particles is explained by elastic interaction between the particles, since the relative positions of the particles coincide with local minima of the interaction energy. We performed numerical Monte Carlo simulation of the particle ordering and we obtained a good agreement with the experimental data.

cond-mat.mtrl-sci↗

arXiv2018

Single crystal growth of TIMETAL LCB titanium alloy by a floating zone method

The methodology of single crystal growth of metastable $β$-Ti alloy TIMETAL LCB in an optical floating zone furnace is presented in this paper. Chemical compositions of both precursor material and single crystals were checked. It was found that the concentration of base alloying elements did not change significantly during the growth process, while the concentrations of interstitial elements O and N increased. DSC measurement determined that this concentration shift has a slight impact on ongoing phase transformations, as in the single-crystalline material peak associated with $α$ phase precipitation moves by a few degrees to a lower temperature and peak attributed to diffusion controlled growth of $ω$ particles shifts to a higher temperature. X-ray reciprocal space maps were measured and their simulation showed that the single crystal has a mosaic structure with mean size of mosaic blocks of approximately 60 nm.

cond-mat.mtrl-sci↗