Kinetic and thermodynamic description of intermediary phases formation in Ti-Al system during reactive sintering

Reactive sintering is currently considered as a promising production route for titanium aluminides in many research works. However, the published descriptions of the reaction mechanism are contradictory or lacking, especially at the temperatures below the melting point of aluminium. This work aims to fill this gap, providing the description of the reactive sintering process at the temperatures between 400 and 900 degrees C. The phases' formation sequence and reaction kinetics were studied and explained using experimental model (Ti/Al diffusion couple) and real reactively sintered samples of equiatomic Ti-Al compressed powder blend. Moreover, phase formation was thermodynamically assessed. It was revealed that Ti2Al5 phase formed preferentially. This phase has not been reported previously as a starting phase in reactive sintering. According to results obtained by experimental model, its formation is controlled by diffusion at 700 degrees C. This phase reacted with aluminium forming pure TiAl3 phase or with titanium, resulting in TiAl phase. Subsequently, TiAl phase reacted with titanium, leading to the Ti3Al phase, or with already present Ti2Al5 phase yielding TiAl2 intermetallic compound. Titanium-rich Ti3Al phase could form only at the temperature of 600 degrees C or above

Grain morphology reconstruction of crystalline materials from Laue three-dimensional neutron diffraction tomography

The macroscopic properties of advanced engineering and functional materials are highly dependent on their overall grain orientation distribution, size, and morphology. Here we present Laue 3D neutron diffraction tomography providing reconstructions of the grains constituting a coarse-grained polycrystalline material. Reconstructions of the grain morphology of a highly pure Fe cylinder and a Cu cube sample are presented. A total number of 23 and 9 grains from the Fe and Cu samples, respectively, were indexed and reconstructed. Validation of the grain morphological reconstruction is performed by post-mortem EBSD of the Cu specimen

Synthesis and Magnetic Properties of Carbon Doped and Reduced SrTiO3 Nanoparticles

We report on the studies of the synthesis, structural, and magnetic properties of undoped SrTiO3 (STO), carbon-doped STO:C, and reduced STO STO:R nanoparticles. Fine (similar to 20-30 nm) and coarse (similar to 100 nm) nanoparticles with a single phase of cubic perovskite-type structure were sintered by thermal decomposition of SrTiO(C2O4)(2). Magnetization loops of fine STO:C and STO:R nanoparticles at low temperatures and an almost linear decrease in magnetization with temperature indicate the realization of a soft, ferromagnetic state in them, with a pronounced disorder effect characteristic of doped dilute magnetic semiconductors. Oxidation and particle size increase suppress the magnetic manifestations, demonstrating the importance of surface-related defects and oxygen deficiency in the emergence of magnetism. It was found that oxygen vacancies and doping with carbon make similar contributions to the magnetization, while complementary electron paramagnetic resonance, together with magnetization measurement studies, show that the most probable state of oxygen vacancies, which determine the appearance of magnetic properties, are charged F+ oxygen vacancies and C-impurity centers, which tend to segregate on the surface of nanoparticles

Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake : Nuclear fuel durability enhancement

In this work, we demonstrate and describe an effective method of protecting zirconium fuel cladding against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments. Zr alloy samples were coated with nanocrystalline diamond (NCD) layers of different thicknesses, grown in a microwave plasma chemical vapor deposition apparatus. In addition to showing that such an NCD layer prevents the Zr alloy from directly interacting with water, we show that carbon released from the NCD film enters the underlying Zr material and changes its properties, such that uptake of oxygen and hydrogen is significantly decreased. After 100–170 days of exposure to hot water at 360 °C, the oxidation of the NCD-coated Zr plates was typically decreased by 40%. Protective NCD layers may prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burnup. NCD may also serve as a passive element for nuclear safety. NCD-coated ZIRLO claddings have been selected as a candidate for Accident Tolerant Fuel in commercially operated reactors in 2020

Vztah statickeho a dynamickeho odpevneni aluminidu zeleza Fe_2Al (a odvozenych slitin) a transformacniho procesu pri strukturnim prechodu B2DO_3

Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

The pseudoelasticity and the shape memory effect in CoNiAl alloys

<p><em>The cobalt alloys (close to the CoNiAl stoichiometry) are the less known shape memory alloys. Such behavior is consequence of the martensitic transformation. The pseudoelasticity is caused by the stress-induced martensitic transformation above the equilibrium martensite start temperature from high temperature cubic phase (austenite) to lower symmetry phase (martensite). In CoNiAl the pseudoelastic behavior can be obtained by the high temperature annealing. In presented work the effect of the annealing temperature on both pseudoelastic behavior and microstructure was investigated.</em></p

Crystal structures of eta ''-Cu3+xSi and eta '''-Cu3+xSi

International audienceThe binary phase diagram of Cu-Si is unexpectedly complex in the vicinity of Cu3+xSi. The low-temperature region contains three closely related incommensurately modulated phases denoted, in order of increasing temperature of stability, eta''', eta '' and eta'. The structure analysis of eta' has been reported previously [Palatinus et al. (2011). Inorg. Chem. 50, 3743]. Here the structure model for the phases eta '' and eta''' is reported. The structures could be solved in superspace, but no superspace structure model could be constructed due to the complexity of the modulation functions. Therefore, the structures were described in a supercell approximation, which involved a 4 x 4 x 3 supercell for the eta '' phase and a 14 x 14 x 3 supercell for the eta''' phase. Both structures are very similar and differ only by a subtle symmetry lowering from eta '' to eta'''. A comparison of the structure models of eta '' and eta''' with the reported structure of eta' suggests that the reported structure model of eta' contains an incorrect assignment of atomic types

Crystal structures of eta ''-Cu3+xSi and eta '''-Cu3+xSi

International audienceThe binary phase diagram of Cu-Si is unexpectedly complex in the vicinity of Cu3+xSi. The low-temperature region contains three closely related incommensurately modulated phases denoted, in order of increasing temperature of stability, eta''', eta '' and eta'. The structure analysis of eta' has been reported previously [Palatinus et al. (2011). Inorg. Chem. 50, 3743]. Here the structure model for the phases eta '' and eta''' is reported. The structures could be solved in superspace, but no superspace structure model could be constructed due to the complexity of the modulation functions. Therefore, the structures were described in a supercell approximation, which involved a 4 x 4 x 3 supercell for the eta '' phase and a 14 x 14 x 3 supercell for the eta''' phase. Both structures are very similar and differ only by a subtle symmetry lowering from eta '' to eta'''. A comparison of the structure models of eta '' and eta''' with the reported structure of eta' suggests that the reported structure model of eta' contains an incorrect assignment of atomic types

Fabrication of functional superhydrophobic surfaces on carbon fibre reinforced plastics by IR and UV direct laser interference patterning

The fabrication of functional microstructures on surfaces by laser enables unique material properties and is presently a leading research topic. This work addresses the production of functional hierarchical microstructures on carbon fibre reinforced polymer composites in order to control the wettability properties of the material. Two-beam Direct Laser Interference Patterning using either ultraviolet (263 nm) or infrared (1053 nm) nanosecond laser source is employed to produce melt-free and well-defined hierarchical microstructures on carbon fibre reinforced plastics. The resulting water contact angles after thin film deposition of 1H,1H,2H,2H-Perflorodecyl-triethoxysilane were analysed with respect to structure depth and quality. The maximum static contact angle of 171° is demonstrated for dual hierarchical microstructures composed of 11 µm deep large-scale pillars, covered by 1.7 µm pillars, both fabricated in a single step