Nanolayer CrAlN/TiSiN coating designed for tribological applications

With the goal to produce a hard and tough coating intended for tribological applications, CrAlN/TiSiN nanolayer coating was prepared by alternative deposition of CrAlN and TiSiN layers. In the first part of the article, a detailed study of phase composition, microstructure, and layer structure of CrAlN/TiSiN coating is presented. In the second part, its mechanical properties, fracture and tribological behavior are compared to the nanocomposite TiSiN coating. An industrial magnetron sputtering unit was used for coating deposition. X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used for compositional and microstructural analysis. Mechanical properties and fracture behavior were studied by instrumented indentation and focused ion beam techniques. Tribological properties were evaluated by ball-on-disk test in a linear reciprocal mode. A complex layer structure was found in the nanolayer coating. The TiSiN layers were epitaxially stabilized inside the coating which led to formation of dislocations at interfaces, to introduction of disturbances in the coating growth, and as a result, to development of fine-grained columnar microstructure. Indentation load required for the onset of fracture was twice lower for the nanolayer CrAlN/TiSiN, compared to the nanocomposite TiSiN coating. This agrees very well with their mechanical properties, with H³/E² being twice higher for the TiSiN coating. However, the nanolayer coating experienced less severe damage, which had a strong impact on tribological behavior. A magnitude of order lower wear rate and four times lower steady state friction coefficient were found for the nanolayer coating.     

Matrix Transformation in Boron Containing High-Temperature Co–Re–Cr Alloys

An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr₂Re₃ type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content.     

Deterministic safety study of advanced molten salt nuclear systems for prospective nuclear power

The inter-comparative analysis of the deterministic safety potential of innovative molten salt systems with critical and sub-critical cores is presented for both fast and thermal neutron spectra. The analysis includes two aspects: the choice of an initial level of sub-criticality and the study of multiple unprotected transients which have been simulated on the basis of one-point kinetics and two-point thermo-hydraulic schemes considering realistic feedback effects. Our preliminary results show that even small levels of sub-criticality (2–3 dollars) of cores can improve their safety characteristics significantly.     

Characteristics of planar diodes based on heavily doped GaAs/AlAs superlattices in the terahertz frequency region

Characteristics of ohmic InGaAs contacts in planar diodes based on semiconductor superlattices with a small-area active region (1–10 μm²) are studied. The diodes were formed on the basis of short (18 or 30 periods) heavily doped (10¹⁸ cm⁻³) GaAs/AlAs superlattices with a miniband width of 24.4 meV. The reduced resistance of the ohmic contact was equal to 2×10⁻⁷ Ω cm² at room temperature. It is shown that the properties of fabricated planar diodes make it possible to use these diodes later on in semiconductor devices that operate in the terahertz frequency region in a wide temperature range (4–300 K). __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 9, 2004, pp. 1141–1146. Original Russian Text Copyright ? 2004 by Pavel’ev, Demarina, Koshurinov, Vasil’ev, Semenova, Zhukov, Ustinov.     

An invitation to fiberwise topology: The general framework for multicolored images in pattern recognition and some of its artificial intelligence aspects

We present a short and rather informal account concerning a problem we posed in earlier work, recall our conjecture at the time, and report on our answer today. Specifically, our purpose is to draw attention to fiberwise topology as a possible mathematical tool for formalizing multi-colored images and other complex signals met in pattern recognition (P.R.), to provide some information concerning the mathematical background of the fiber topological machinery, and indicate how to use it. For a detailed technical study as well as a tentative hierarchical classification of topological images in growing order of complexity and the corresponding topological processing methods, the readers may consult Pavel [5]. The paper ends by mentioning some artificial intelligence (A.I.) aspects of the fiberwise imagery.     

Development of catalysts for hydrogen generation from hydride compounds

Catalytic hydrolysis of NaBH₄ and NH₃BH₃ has been studied. It was shown that the nature of the support and the active component of the catalyst affect the H₂ generation rate. Despite similar sizes of rhodium particles formed on the surface of different supports (γ-Al₂O₃, TiO₂, carbon), their reactivity is different. Rh/TiO₂ with low rhodium concentration (1 wt.%) is the most active catalyst both in the hydrolysis of NaBH₄ and NH₃BH₃. The obtained results show that the rhodium chloride interaction with titania determines the reactivity of rhodium particles formed under action of NaBH₄ medium. TEM, DRS UV–vis and XPS were used to characterize the catalysts.