FEATURES OF DEFORMATION AND FRACTURE OF TI–6AL–4V ALLOYS MANUFACTURED BY SELECTIVE LASER MELTING

We studied the structure and mechanical properties of Ti–6Al–4V samples manufactured by the selective laser sintering (SLS) method, which were grown at different angles to the construction platform. The influence of the angle of inclination of the sample on the mechanical properties is revealed. It is shown that the rate of stretching has a significant effect on the mechanical properties of the samples.Исследована структура и механические свойства Ti–6Al–4V образцов, полученных методом селективного лазерного сплавления (СЛС), которые были выращены под различными углами к платформе построения. Обнаружено влияние угла наклона образца на механические свойства. Показано, что скорость растяжения оказывает существенное влияние на механические свойства образцов.Работа выполнена при поддержке гранта РФФИ № 17-03-000-84

Structure of 3D Printed Ti-6Al-4V Alloy after Low-frequency Processing

The structure and residual elastic stresses in 3D printed (Selective laser melting) Ti-6A1-4V samples after the low-frequency vibration processing were investigated. The studied samples were manufactured horizontally in respect to the building platform. Different vibration oscillations modes (vertical, horizontal, and elliptical) were chosen for study. The oscillations were done with frequency of 16 Hz, and a processing time was 20 minutes. Studies shown that 3D printed samples had a high level of residual elastic stresses, which were changed after vibration treatment. The influence of the low-frequency processing on the phase composition of the alloy was found. © Published under licence by IOP Publishing Ltd

Identifying chromophore fingerprints of brain tumor tissue on hyperspectral imaging using principal component analysis

Hyperspectral imaging (HSI) is an optical technique that processes the electromagnetic spectrum at a multitude of monochromatic, adjacent frequency bands. The wide-bandwidth spectral signature of a target object's reflectance allows fingerprinting its physical, biochemical, and physiological properties. HSI has been applied for various applications, such as remote sensing and biological tissue analysis. Recently, HSI was also used to differentiate between healthy and pathological tissue under operative conditions in a surgery room on patients diagnosed with brain tumors. In this article, we perform a statistical analysis of the brain tumor patients' HSI scans from the HELICoiD dataset with the aim of identifying the correlation between reflectance spectra and absorption spectra of tissue chromophores. By using the principal component analysis (PCA), we determine the most relevant spectral features for intra- and inter-tissue class differentiation. Furthermore, we demonstrate that such spectral features are correlated with the spectra of cytochrome, i.e., the chromophore highly involved in (hyper) metabolic processes. Identifying such fingerprints of chromophores in reflectance spectra is a key step for automated molecular profiling and, eventually, expert-free biomarker discovery

Oxygen and nitrogen concentrations in the Ti-6Al-4V alloy manufactured by direct metal laser sintering (DMLS) process

Published ArticleTwo machines from two scientific centers (Russia and South Africa) were used for the manufacturing of the Ti6Al4V alloys by the direct metal laser sintering. The chemical composition of powders complies with the ASTM F-136 (grade 5), ASTM B348 (grade 23) standard for medical applications. Analysis of the oxygen and nitrogen contamination in DMLS alloys was done with Van de Graaff accelerator with two Mega Volts. It is found that structures of the samples manufactured with two different machines used the same regimes are close to each other. TEM studies found the metastable martensitic structure and silicon nitride Si3N4. It was found that the oxygen and nitrogen contents in both samples are within the normal range for medical grade titanium alloys

Comparative analysis of the structure and internal stress in Ti-6Al-4V alloys manufactured by 3D printing and processing with screw extrusion

Study is based on the compare characterization of the structure and evaluation of the residual internal stresses in Ti-6Al-4V samples manufactured by the 3D printing (selective laser melting) and in the Ti-6Al-4V samples obtained with using of the severe plastic deformation by screw extrusion. The microstructure and residual stresses were examined by transmission electron microscope and X-ray diffractometer. High tensile internal residual stresses in the 3D printed sample were found. The high compressive residual internal stresses were found in the hot pressed and in the twisted samples. It was shown that arising of the high residual stresses in the studied samples under various technological processes occurred in various ways. The residual stresses in the severe plastic deformed samples arose due to non-uniform volumetric plastic deformation. In 3D printed sample, the residual tensile stresses arose from both phase (martensitic) transformation and thermal deformation. © Published under licence by IOP Publishing Ltd

Phase Transitions in the Co–Al–Nb–Mo System

Phase transitions in the Co-rich part of the Co–Al–Nb–Mo phase diagram are studied by energy dispersive spectroscopy (EDS), X-ray analysis, transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) measurements. The obtained results were compared with the results for alloys of the binary Co–Al and ternary Co–Al–Nb, and Co–Al–Mo systems. Formation of the intermetallic phase with the L12 structure was found in a range of alloys with 10 at.% Al, 2–9 at.% Nb, and 3–7 at.% Mo. Intermetallic compound Co2Nb, Laves phase with the different chemical composition and crystal structure (C14 and C36) was detected in the Co–Al–Nb and Co–Al–Nb–Mo samples after vacuum solution treating at 1250◦C for 30 h. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This work was founded by the Russian Foundation for Basic Research (RFBR), project No. 20-33-70221 and Russian State program of Institute of Metal Physics "Additivity" № 121102900049-1

Trimer Formation and Metal-Insulator Transition in Orbital Degenerate Systems on a Triangular Lattice

As a prototypical self-organization in the system with orbital degeneracy, we theoretically investigate trimer formation on a triangular lattice, as observed in LiVO2. From the analysis of an effective spin-orbital coupled model in the strong correlation limit, we show that the previously-proposed orbital-ordered trimer state is not the lowest-energy state for a finite Hund's-rule coupling. Instead, exploring the ground state in a wide range of parameters for a multiorbital Hubbard model, we find an instability toward a different orbital-ordered trimer state in the intermediately correlated regime in the presence of trigonal crystal field. The trimer phase appears in the competing region among a paramagnetic metal, band insulator, and Mott insulator. The underlying mechanism is nesting instability of the Fermi surface by a synergetic effect of Coulomb interactions and trigonal-field splitting. The results are compared with experiments in triangularlattice compounds, LiVX2 (X=O, S, Se) and NaVO2.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp