Hydrogen degradation of steels in gas mains after long periods of operation

We study the degradation of the mechanical and corrosion properties of 17G1S steel in gas mains as a result of operation for 28–40 yr. We reveal the simultaneous decrease in its strength and hardness, on the one hand, and impact toughness and crack resistance, on the other hand. The indicated parameters prove to be most sensitive to the in-service degradation of the metal. The degradation of steel leads to the increase in the strain-hardening coefficient and the appearance of the yield plateau in the tensile stress-strain diagram and causes the appearance of sensitivity to hydrogen embrittlement increasing in the process of operation. We analyze the role of absorbed hydrogen affecting the mechanism of strain aging and responsible for the appearance of defects. It is shown that the polarization resistance can be used not only for monitoring of the corrosion state of gas pipelines but also for the prediction of changes in their mechanical properties in the process of operation. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 5, pp. 97–104, September–October, 2007.     

Fabrication of Strain-Relaxed Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript>x</Subscript>/Si(001) Buffer Layers of Low Surface Roughness

The results are presented of the fabrication of strain-relaxed graded Si_{1 − x} Ge_x/Si(001) buffer layers with a maximum Ge fraction of about 0.25 that have a low density of threading dislocations (<10⁶ cm⁻²) and low surface roughness. The buffer layers are grown by atmospheric-pressure hydride CVD. It is found that chemical mechanical polishing can reduce their surface roughness to a level comparable with that of the original Si(001) substrates. It is shown that the polished buffer layers can serve as substrates for MBE-grown SiGe/Si heterostructures.__________Translated from Mikroelektronika, Vol. 34, No. 4, 2005, pp. 243–250.Original Russian Text Copyright © 2005 by Vostokov, Drozdov, Krasil’nik, Kuznetsov, Novikov, Perevoshchikov, Shaleev.     

Kinetics of small fatigue cracks in steel during cyclic loading

The kinetics of development of fatigue microcracks in a high-strength 08Kh14AN4MD steel is studied when a cantilever specimen with several notches is subjected to rotational bending tests. The specific feature of the tests consists in the fact that, when the specimen is loaded at a constant load, different stress amplitudes are realized in different notches. As a result, after the sample has failed across the section with the maximum stress, a longitudinal polished section of the specimen contains fatigue cracks having nucleated in the mouths of the other notches at lower stress amplitudes. A relation between inflection points in the fatigue curve and the conditions of local and developed yield in a notch has been established. Fatigue fracture mechanisms at a superhigh number of loading cycles are studied, and their relation to the structure near a crack is found. A rapid method for estimating the fatigue limit at a superhigh number of loading cycles is proposed.     

A note on the variance of rank-based selection strategies for genetic algorithms and genetic programming

This paper evaluates different forms of rank-based selection that are used with genetic algorithms and genetic programming. Many types of rank based selection have exactly the same expected value in terms of the sampling rate allocated to each member of the population. However, the variance associated with that sampling rate can vary depending on how selection is implemented. We examine two forms of tournament selection and compare these to linear rank-based selection using an explicit formula. Because selective pressure has a direct impact on population diversity, we also examine the interaction between selective pressure and different mutation strategies.     

Three-dimensional structure of the cloud of a carbon pellet evaporated in plasma of Wendelstein 7-AS stellarator

Experiments performed on a Wendelstein 7-AS stellarator revealed asymmetry of the cloud of an ablating carbon pellet. The cloud is elongated in the direction of large radius toward stronger fields, that is, opposite to the direction expected due to the toroidal drift. In order to study the effect in more detail, the three-dimensional structure of the cloud was analyzed by computer tomography. The results confirmed asymmetry of the cloud. This asymmetry is related to a drift flow existing in the plasma and directed along large radius toward stronger fields. The drift velocity is numerically estimated at ～300 m/s.     

Micromechanism of corrosion fracture of the plates of heat exchangers

We have studied the micromechanism of corrosion fracture of heat-transfer plates of a heat exchanger. The operation of heat exchangers under conditions of contamination of the plates with a sediment from water leads to their local corrosion under the sediment. The conditions of operation of the heat exchangers being equal, heat-transfer plates made of AiSi316Ti steel worked 2.36 times as long as those of AiSi304L steel. The corrosion fracture of plates under the sediment began from pitting initiation near nonmetallic inclusions of a certain nature. Afterwards, these pittings built up into corrosion spots by the mechanism of stress corrosion and hydrogen embrittlement. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 110–116, January–February, 2007.     

Refractory Ceramics Based on Local Materials

A technology for producing ShA and ShB refractories uses high-melting clays from the Rostov Region and high-alumina technogenic waste. The effect of the chamotte-to-clay ratio, the granulometric composition, and the additive introduction method on the properties of products is investigated.__________Translated from Steklo i Keramika, No. 1, pp. 15 – 16, January, 2005.     

Tunneling spectroscopy of palladium-barium emitters

The surface of a palladium-barium cathode was studied using scanning probe microscopy techniques. Data from the tunneling spectroscopy showed the pattern of the electron work function distribution over a microscopic region on the emitter surface. This pattern is compared to the distribution of various phases in the palladium-barium alloy employed.     

Structure and properties of porous silicon obtained by photoanodization

The results of an investigation of layers of porous silicon (PS), which was obtained by electrochemical etching of p-Si under different illumination conditions — natural light, incandescent light, and light from a mercury lamp with and without a filter — are reported. The structure of the layers was studied by double-crystal x-ray diffractometry, the composition was monitored by means of the IR absorption spectra, and the radiative properties were monitored according to the photoluminescence (PL) spectra. It was established that electrochemical etching under illumination produces PS with a higher porosity and more intense PL whose maximum is shifted into the short-wavelength region. These changes are accompanied by a large disordering of the structure and an increase in the oxygen content in the layer. It is concluded that illumination accelerates the chemical interaction of PS with the electrolyte due to oxidation. High-porosity porous silicon stored in air exhibits quenching of PL. Conversely, PL is excited in layers with a lower porosity. Aging of PS is characterized by an increase in the microdeformation of the layers, a decrease in the crystallite sizes with a partial loss of coherence between the crystallites and the substrate, and an increase in the fraction of the amorphous phase. Fiz. Tekh. Poluprovodn. 31, 1261–1268 (October 1997)     

Organizing the production of heat-insulating inserts for ingot-mold hot tops

The Zlatoust Metallurgical Plant has developed a technology that employs semi-dry pressing to make two-layer (composite) heat-insulating inserts for ingot-mold hot tops. The working layer is made of a mixture of materials based on quartz sand, while the insulating layer is based on foamed vermiculate. The binders are sodium silicate solution and commercial lignosulfonate with a density of 1.12–1.20 g/cm³.