Phase equilibria in the nickel corner of the Mo-Ni-B system at temperatures close to melting

The Mo-Ni-B alloys prepared by arc-melting are examined in as-cast and annealed states using x-ray diffraction, scanning electron microscopy with electron probe microanalysis, and differential thermal analysis. The temperatures of invariant equilibria are refined. The projections of liquidus and solidus surfaces are plotted for the Ni-rich region.     

Thermal fatigue of a heat-resistant Fe-0.45C-26Cr-33Ni-2Si-2Nb alloy

The thermal fatigue of a heat-resistant Fe-0.45C-26Cr-33Ni-2Si-2Nb alloy is studied during thermal cycling in the temperature range 50–900°C up to 1000 cycles. The alloy is investigated in the initial as-cast state and after isothermal annealing during 1000 h at a temperature of 800, 900, 1000, or 1100°C; these conditions imitate the temperature conditions of operation and the structural state of various layers in a reaction pipe in the radiant furnace coils of ethylene production installations. After isothermal annealing, the thermal fatigue life of the alloy is found to decrease by a factor of 1.7–1.2 as compared to the initial as-cast state. It is shown that isothermal annealing and subsequent thermal cycling lead to the formation of carbide precipitates of various sizes in the alloy structure that affect the thermal fatigue life of the alloy. Thermal fatigue cracks are shown to form and grow predominantly at the sites of accumulation of fine carbide precipitates. Coarse (>10 μm) precipitates retard crack growth, and cracks branch near such precipitates.     

Determination of the parameters of circuit models of resistive microwave structures

New methods of determining the parameters of circuit models of resistive microwave structures are considered, based on a measurement of the wave scattering parameters of the contact device, consisting of coaxial-stripline transitions, a stripline transmission line and the structure analyzed. Results which demonstrate the high efficiency of the proposed methods of solving the problem are presented. __________ Translated from Izmeritel'naya Tekhnika, No. 8, pp. 51–55, August, 2008.     

Nonlinear optical absorption in a heavily doped degenerate n-GaAs

The nonlinear optical absorption in a heavily doped degenerate n-GaAs in the spectral region near the fundamental absorption edge was studied. The relative contribution of the effects of states’ filling, band-gap narrowing, and screening of the tails of density of states by photoexcited charge carriers to the nonlinear optical absorption was analyzed on the basis of the quasi-classical model of fluctuation levels. An experimentally observed increase in optical transmission was shown to be mainly caused by the dynamic states’ filling effect.     

Influence of Hydrogen on the Equilibrium of a Dislocation Submicrocrack in α-Iron

Numerical methods are used to analyze the influence of hydrogen on the fracture of steels with bcc lattice by the mechanism of microcleavage. The behavior of submicrocracks at the head of a dislocation pileup is studied under uniaxial tension. In the case of delivery of hydrogen by merged dislocations of the pileup into the submicrocrack, it loses stability due to the adsorption decrease in the specific surface energy earlier than it becomes possible under the action of the pressure of hydrogen in the crack. We deduce the dependences of the fracture stress on the specific surface energy and the amount of hydrogen delivered by dislocations into the submicrocrack. The influence of hydrogen condensed on dislocations on the formation of submicrocracks is significant. We establish the relationship between the amount of hydrogen condensed on dislocations, the concentration of diffusing hydrogen in the metal, and rapid degradation of mechanical properties of steel even for small concentrations of dissolved hydrogen.     

A new efficient algorithm for computing the imprecise reliability of monotone systems

Reliability analysis of complex systems by partial information about reliability of components and by different conditions of independence of components may be carried out by means of the imprecise probability theory which provides a unified framework (natural extension, lower and upper previsions) for computing the system reliability. However, the application of imprecise probabilities to reliability analysis meets with a complexity of optimization problems which have to be solved for obtaining the system reliability measures. Therefore, an efficient simplified algorithm to solve and decompose the optimization problems is proposed in the paper. This algorithm allows us to practically implement reliability analysis of monotone systems under partial and heterogeneous information about reliability of components and under conditions of the component independence or the lack of information about independence. A numerical example illustrates the algorithm.     

Safety analysis of a multi-phased control system

In the paper we focus on the analysis the efficiency of the control system to ensure the safety by emergency situations. The system is modeled as a multi-phased system. The peculiarity of the considered system is that it supervises a state of a control object and does not make any impact on the object before accident occurrence. After an emergency occurrence the system generates the response for coping with this situation. We propose a measure of the system efficiency for evaluating the system safety. A numerical example illustrates the proposed approach for computing the system efficiency.     

A new heuristic method redundancy optimization in a consecutive-k-out-of-n:F system by fuzzy probability

In this paper it is presented heuristic method and its modification for solution of the redundancy optimization problem by fuzzy failure probabilities. This method is considered for consecutive-k-out-of-n:F system due to simplified expression for reliability importance of components. Method is based on the fuzzification and on the fuzziness importance of failure probabilities.     

Comparative analysis of structure and phase composition for alloys 45Kh26N33S2B2 and 45X25H20C2 after long-term exposure to high temperatures and static load

Electron microscopy was used to determine the nature of the structural changes in 45Kh26N33S2B2 alloy’ and the nature and chemical composition of proeutetoid constituents’ based on tests of samples of this material for long-term strength at high temperature.