New Ideas on the Mechanism of Structure Formation in Nitrided Steels

The main laws of formation of structure and properties of nitrided structural steels are studied depending on their composition, parameters of preliminary heat treatment, and nitriding modes. New factors controlling the structure and operational properties based on new concepts of the mechanism of formation of nitride particles in the nitriding process are determined.     

Developing an Algorithm for the Calculation of a Painting Chamber

Theoretical Foundations of Chemical Engineering - This team of authors presents the development of an algorithm and its practical application in the software for solving the problems of...     

Stress relaxation in zirconium carbide. Report 2. Mechanisms of stress relaxation. The relationship of the processes of creep and relaxation

Mechanisms of stress relaxation in ZrC_1.00 (d=6–35 .m) in the area of the ductile-to-brittle transition temperature (1600–2200C) are considered. It is established that in the 1800–2000C range for ZrC_1.00 with grain sizes of 6 and 14–35 m, respectively, stress relaxation occurs as the result of pure grain boundary slip while at higher temperatures by intragranular cross slip. It is shown that creep in the steady stage and stress relaxation in ZrC_1.00 with grain sizes of 6–35 m are controlled by different physical processes, which makes impossible obtaining for these materials of data on stress relaxation by conversion with use of information on steady creep.Translated from Problemy Prochnosti, No. 2, pp. 55–60, February, 1994.     

Strength of the pyroceram So115M under lengthy static loading

The article presents the results of long-time strength tests of the casting pyroceram SO115M at room temperature by the method of three-point bending. We obtained the power dependence of the time to failure _f on the applied load : _f ^–11.7.Translated from Problemy Prochnosti, No. 1, pp. 102–104, January, 1996.     

Transfer of iron to Cu–Ni alloys from the lining of the vacuum induction furnace

In Ni–Cu alloys, iron must be excluded in many cases. Iron may enter the alloy from the batch or the furnace lining. Since the Fe₂O₃ content in refractories may be as much as 2.5%, it is important to assess the increase in iron content in alloys on account of interaction with the furnace lining. In the present work, the influence of the Fe₂O₃ content in the crucible and the volume of the crucible on the iron content in the final alloy is studied. Thermodynamic analysis and experimental data indicate that the nickel and copper in Ni–Cu alloys may reduce iron that is present in the lining. When using low-iron batch, iron from the crucible is transferred almost completely to the melt. The increase in iron content in Ni–Cu alloys is investigated as a function of the capacity of the vacuum induction furnace and the Fe₂O₃ content in the periclase crucibles, with complete transfer of the iron from the lining to the melt. With increase in furnace capacity, less iron enters the melt from the crucible. With more than 200 kg of metal, the increase in iron concentration mainly depends not on the furnace capacity but on the Fe₂O₃ content in the refractory. In order to produce Ni–Cu alloys with <0.01% Fe, refractories with Fe₂O₃ content no higher than 0.5% must be used. To produce Ni?Cu alloys with <0.05% Fe, the use of lining refractories with Fe₂O₃ content no higher than 2.5% is recommended.     

Pressure effect on the phase transformations and structure of an Al-12 at % Si alloy

Phase transformations of an Al-12 at % Si alloy have been studied by differential barothermal analysis at temperatures of up to 700°C in argon compressed to 100 MPa. Heating at a rate of 8°C/min under a pressure of 100 MPa has been shown to increase the temperature of the L → (Al) + Si eutectic transformation in the alloy by 4°C. After crystallization of the binary eutectic, the differential thermal analysis cooling curve showed an additional exothermic peak, corresponding to the decomposition of the aluminum-based solid solution (Al) at 547°C and precipitation of silicon particles in the nanometer range. A barothermal scanning cycle reduced numerical porosity characteristics of the alloy, except for the pore number density. The lattice parameter of silicon microparticles in the alloy approaches values in the literature, whereas that of nanoparticles is slightly greater. The lattice parameter of the aluminum remains unchanged during crystallization and cooling in compressed argon. The microhardness of the aluminum matrix of the alloy corresponds to that of pure aluminum.     

High-pressure phase transformations, microstructure, and magnetic properties of the hypereutectic alloy 10Ni-90Al

Phase transformations of the hypereutectic alloy 10Ni-90Al have been studied by differential barothermal analysis at temperatures of up to 900°C and pressures of up to ?100 MPa. We have determined the pressure coefficients of the liquidus and solidus temperatures and the temperatures of solid-state dissolution and precipitation of the intermetallic phase Al₃Ni. At high pressures, the solid-state decomposition of the supersaturated solid solution of nickel in aluminum occurs at 622°C and yields an (Al) + Al₃Ni mixture. We assume that, during cooling of the alloy at high pressure, intermetallic particles form in three steps. Barothermal analysis data have been compared to the canonical t-x phase diagram of the Al-Ni system. As a result of melting and crystallization at high pressure, the microcrystalline structure of the as-prepared alloy transforms to a macrocrystalline, dendritic structure and the micropore concentration increases. X-ray diffraction data indicate an increase in the unit-cell volumes of the Al and Al₃Ni in the alloy crystallized at 100MPa. We have studied the magnetic properties of the alloy after barothermal analysis.     

Untersuchungen zur Spin-Trapping-Kinetik in Systemen von Radikalen unterschiedlicher Reaktivität. Die Photolyse von α-Phenylbenzoin in Gegenwart von Benzyliden-tert.-butylamin-N-oxid

Investigations on Spin-Trapping Kineties in Radical Systems with Different Reactivity. Photolyses of α-Phenylbenzoine in the Presence of Benzylideneter. -butylamine N-oxide As a model system to study the spin-trapping kinetics of systems forming two radicals of different reactivity α-phenylbenzoine (PhB) was chosen. The photolysis of PhB forms benzoyl (B·) and diphenylketylradikals (K·), respectively, which can be trapped by benzylidene-tert-butyl-amine N-oxide (PBN), as a spin trap. The rate constants of radical addition to PBN and their reactions with the spin adducts were determined by means of flash photolysis and kinetic calculations of the PBN concentration dependence. For B· and K· addtion rate constants to PBN of k₁ = 8,1 × 10⁵ M⁻¹s⁻¹, and k₂ = 5,8 · 10⁴ M⁻¹s⁻¹, respectively, were found. The rate constants for the reactions of B· and K· with the spin adducts are in the order of 10⁹…10¹⁰ M⁻¹s⁻¹.