Search

β-FeSi2 with the addition of B4C nanoparticles was manufactured by sintering mechanically alloyed Fe and Si powders with Mn, Co, Al, P as p and n-type dopants. The consolidated samples were subsequently annealed at 1123 K for 36 ks. XRD analysis of sinters after annealing confirmed nearly full transformation from α and ε into thermoelectric β-FeSi2 phase. SEM observations of samples surface were compliant with the diffraction curves. TEM observations allowed to depict evenly distributed B4C nanoparticles thorough material, with no visible aggregates and establish grain size parameter d2 < 500 nm. All dopants contributed to lower thermal conductivity and Seebeck coefficient, with Co having strongest influence on increasing electrical conductivity in relation to reference FeSi2. Combination of the addition of Co as dopant and B4C nanoparticles as phonon scatterer resulted in dimensionless figure of merit ZT reaching 7.6 × 10–2 at 773 K for Fe0.97Co0.03Si2 compound. Comparison of the thermoelectric properties of examined sinters to the previously manufactured of the same stoichiometry but without B4C nanoparticles revealed theirs overall negative influence.

Precipitation strengthening is one of the most effective strengthening mechanisms in metallic alloys. Its effectiveness depends on the number density of small precipitates homogenously distributed in the matrix. In this work, an attempt has been made to accelerate precipitation and thus precipitation strengthening in an AlCuMg alloy though a specially designed thermo-mechanical treatment. Solution heat treatment has been carried out before and directly after heavy rolling followed by conventional ageing in order to study homogenous nucleation of GPB zones. It appeared that samples solutionized after plastic deformation feature much higher hardness as well as density of precipitates when compared to ones after conventional treatment. The reasons of this unexpected outcome had been studied by means of differential scanning calorimetry and transmission electron microscopy. It was found that the evolution of GPB zones and further phases vary depending on the pre-ageing history. Diffusion-based phenomena controlling the nucleation seems to be accelerated in samples heat treated directly after the rolling. Based upon the affinity of solutes to the vacancies it has been deduced that magnesium plays a critical role in binding and releasing vacancies during the thermo-mechanical procedure. As a result, GPB zones are present in very early stages of ageing providing nucleation sites for the most strengthening precipitates which are fine and densely distributed within grains. An atomistic model for nucleation of early precipitates is discussed on the basis of DSC measurements, STEM analysis and data available in literature.

Microstructure and nanohardness of a nearly equimolar W-Ta-Cr-V high entropy alloy (HEA), as well as its irradiation response under He+ irradiation, were investigated. The single-phase body-centered cubic nanostructured alloy with a 1 µm thick layer was fabricated on a silicon substrate using a magnetron sputtering method. The HEA film has a complex microstructure consisting of micrometric domains that exhibit internal nanostructure controlled by their crystal orientation. The measured nanohardness of the W-Ta-Cr-V alloy is 13 ± 2 GPa, which significantly exceeds the hardness of nanocrystalline tungsten as a result of the high solid-solution strengthening effect. In order to evaluate the irradiation resistance of the HEA film, the material was irradiated with 200 keV He+ ions at room temperature, with two different ion fluences: 1 × 1016 and 5 × 1016 ions/cm2. Using transmission electron microscopy, a high density of extremely fine He bubbles is observed that were uniformly distributed in the matrix. The increase of He+ ion fluence increased the density of bubbles, whereas their size remained at a similar level, which indicates that the damage proceeds by the nucleation of additional He bubbles, not by their growth.

Significant hardening effect due to Fe concentrations in Ni-based alloys with face-centered-cubic structure has been studied by using a combined experimental and atomistic-based computational approach via nanoindentation tests. The obtained experimental load–displacement data for the [001] crystal orientation reached a qualitative good agreement with molecular dynamics simulations results, leading to strong evidence that the main strengthening factors are associated to sluggish dislocation diffusion, reduced defect sizes and the nucleation of tetrahedral stacking faults. Here, interstitial type prismatic dislocation loops mainly formed by ⅙〈112〉 Shockley dislocations are nucleated during the loading process, where their interaction leads to the formation of pyramidal shaped stacking fault which are mainly created by ⅓〈100〉 Hirth dislocations lines. Observing both types of defects coexisting in the same plastic deformation zone by both approaches. Reported mechanical data, measured experimentally and interpreted numerically, are also in accordance with microstructural SEM and TEM investigations.

Polycrystalline tungsten (W) samples were simultaneously irradiated by 10.8 MeV W ions and exposed to 300 eV deuterium (D) ions at different temperatures ranging from 450 K to 1000 K. After simultaneous W ion irradiation and D ion exposure the samples were additionally exposed to low-energy D ions at 450 K in order to populate all the defects created beforehand. The amount of damage created was evaluated by measuring D depth profiles and D thermal desorption spectra. Results were compared with data obtained in a sequential experiment where samples were first irradiated by 10.8 MeV W ions and only afterwards exposed to 300 eV D ions at 450 K to populate the created defects. At 450 K we observed a two times higher maximum D concentration for the simultaneous case as compared with the sequential case. At 600 K and 800 K the ratio between the simultaneous and sequential case decreases to about 1.6 and 1.2, respectively, and increases again to a factor of 2 at 1000 K. We attribute this dependence on temperature to the change in the concentration of mobile and trapped D during the simultaneous exposures, which is in line with theoretical calculations predicting that trapped D in a vacancy prevents vacancy annihilation with self-interstitials. [ABSTRACT FROM AUTHOR]

Literature data has shown that reactive oxygen species (ROS), generated by immune cells during post-operative inflammation, could induce corrosion of standard Ti-based biomaterials. For Ti6Al4V alloy, this process can be further accelerated by the presence of albumin. However, this phenomenon remains unexplored for Ti β-phase materials, such as TiNb alloys. These alloys are attractive due to their relatively low elastic modulus value. This study aims to address the question of how albumin influences the corrosion resistance of TiNb alloy under simulated inflammation. Electrochemical and ion release tests have revealed that albumin significantly enhances corrosion resistance over both short (2 and 24 h) and long (2 weeks) exposure periods. Furthermore, post-immersion XPS and cross-section TEM analysis have demonstrated that prolonged exposure to an albumin-rich inflammatory solution results in the complete coverage of the TiNb surface by a protein layer. Moreover, TEM studies revealed that H 2 O 2 -induced oxidation and further formation of a defective oxide film were suppressed in the solution enriched with albumin. Overall results indicate that contrary to Ti6Al4V, the addition of albumin to the PBS + H 2 O 2 solution is not necessary to simulate the harsh inflammatory conditions as could possibly be found in the vicinity of a TiNb implant., (© 2024 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals LLC.)

In hexagonal materials, (a+c) dislocations are typically observed to dissociate into partial dislocations. Edge (a+c) dislocations are introduced into (0001) nitride semiconductor layers by the process of plastic relaxation. As there is an increasing interest in obtaining relaxed InGaN buffer layers for the deposition of high In content structures, the study of the dissociation mechanism of misfit (a+c) dislocations laying at the InGaN/GaN interface is then crucial for understanding their nucleation and glide mechanisms. In the case of the presented plastically relaxed InGaN layers deposited on GaN substrates, we observe a trigonal network of (a+c) dislocations extending at the interface with a rotation of 3° from <1 1 ¯ $\bar 1$ 00> directions. High-resolution microscopy studies show that these dislocations are dissociated into two Frank-Shockley 1/6<2 2 ¯ $\bar 2$ 03> partial dislocations with the I 1 BSF spreading between them. Atomistic simulations of a dissociated edge (a+c) dislocation revealed a 3/5-atom ring structure for the cores of both partial dislocations. The observed separation between two partial dislocations must result from the climb of at least one of the dislocations during the dissociation process, possibly induced by the mismatch stress in the InGaN layer., (© 2023 Royal Microscopical Society.)

This study explores the suitability of (Cd,Mn)Te and (Cd,Mn)(Te,Se) as room-temperature X-ray and gamma-ray detector materials, grown using the Bridgman method. The investigation compares their crystal structure, mechanical and optical properties, and radiation detection capabilities. Both crystals can yield large-area single crystal samples measuring approximately 30 × 30 mm 2 . In low-temperature photoluminescence analysis, both materials showed defect states, and annealing in cadmium vapors effectively eliminated donor-acceptor pair luminescence in (Cd,Mn)Te but not in (Cd,Mn)(Te,Se). Moreover, harder (Cd,Mn)(Te,Se) exhibited a higher etch pit density compared to softer (Cd,Mn)Te. X-ray diffraction examination revealed uniform lattice constant distribution in both compounds, with variations at a part per million level. (Cd,Mn)Te crystals demonstrated excellent single crystal properties with narrower omega scan widths, while (Cd,Mn)(Te,Se) exhibited a high contribution of block-like structures with significantly larger misorientation angles. Spectroscopic evaluations revealed better performance of a pixelated (Cd,Mn)Te detector, in comparison to (Cd,Mn)(Te,Se), achieving a mean full width at half maximum of 14% for the 122 keV gamma peak of Co-57. The reduced performance of the (Cd,Mn)(Te,Se) detector may be attributed to deep trap-related luminescence or block-like structures with larger misorientation angles. In conclusion, Bridgman-grown (Cd,Mn)Te emerges as a more promising material for X-ray and gamma-ray detectors when compared to (Cd,Mn)(Te,Se).

In this work, the comparison of microstructure, texture, and mechanical properties of the newly developed TZ61 (Mg-6Sn-1Zn) alloy with the commercially available AZ61 (Mg-6Al-1Zn) has been presented. Both analyzed Mg alloys were processed by conventional symmetric and asymmetric rolling (i.e., Differential Speed Rolling-DSR). The microstructure and texture were examined by EBSD and XRD, whereas the mechanical behavior was investigated by uniaxial tensile tests. DSR processing led to more effective grain refinement of both TZ61 and AZ61 sheets. However, a high fraction of Mg 2 Sn phase precipitates in the TZ61 sheets hindered grain growth what resulted in their smaller grain size as compared to AZ61 sheets. DSR processing lowered also the basal texture intensity in the TZ61 and AZ61 sheets. A unique basal poles splitting was observed for the as-rolled TZ61 alloy, while AZ61 alloy exhibited a typical single-peak basal texture. Finally, the reduced grain size and weakened basal texture by DSR processing caused increase of plasticity of the annealed TZ61 and AZ61 sheets. Nevertheless, the annealed AZ61 sheets showed higher uniform elongation and strength (as compared to TZ61 ones), which has been attributed to their significantly lower texture intensity and greater ability to strain hardening.

The effect of shear deformation introduced by differential speed rolling (DSR) on the microstructure, texture and mechanical properties of Mg-6Sn alloy was investigated. Mg-6Sn sheets were obtained by DSR at speed ratio between upper and lower rolls of R = 1, 1.25, 2 and 3 (R = 1 refers to symmetric rolling). The microstructural and textural changes were investigated by electron backscattered diffraction (EBSD) and XRD, while the mechanical performance was evaluated based on tensile tests and calculated Lankford parameters. DSR resulted in the pronounced grain refinement of Mg-6Sn sheets and spreading of basal texture as compared to conventionally rolled one. The average grain size and basal texture intensity gradually decreased with increasing speed ratio. The basal poles splitting to transverse direction (TD) or rolling direction (RD) was observed for all Mg-6Sn sheets. For the as-rolled sheets, YS and UTS increased with increasing speed ratio, but a significant anisotropy of strength and ductility between RD and TD has been observed. After annealing at 300 °C, Mg-6Sn sheets became more homogeneous, and the elongation to failure was increased with higher speed ratios. Moreover, the annealed Mg-6Sn sheets were characterized by a very low normal anisotropy (0.91-1.16), which is normally not achieved for the most common Mg-Al-Zn alloys.

Developmental anomalies of the breast are frequently observed in women. The most serious pathology is gigantomastia. This type of breast hypertrophy may be caused by hypersensitivity of the breast oestrogen and progesterone receptors, by disturbances of the normal balance of oestrogen and androgen hormones, by hyperthyroidism or by hormonal activity of the neoplasm. In most cases gigantomastia produces pathological changes in the vertebral column which become manifest as discopathia, scoliosis or scoliokyphosis. A case of gigantomastia treated with surgery is presented and the effect of plastic operation is demonstrated. Surgery may be recommended as an excellent therapeutic treatment of gigantomastia.