Grain boundary migration during heating of an ensemble of small molybdenum particles

Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 83–89, June, 1992.     

Embrittlement of nanocrystalline nickel by liquid metals

Metallographic and fractographic tests of liquid metal embrittlement are performed for nanocrystalline Ni-Hg systems. It is shown that the behaviour of nanocrystalline nickel under these conditions is close to that of ordinary polycrystalline materials. The presence of a stage of subcritical crack growth is demonstrated. As nanocrystalline grains have none of their own intrinsic dislocations, it is assumed that subcritical crack growth in liquid metal environment can be realized through the mechanism of dissolution of atoms from the crack tip. This dissolution-condensation model of liquid metal embrittlement, developed for polycrystals, can also be applied to nanocrystals.     

Charged Surface of Liquid Hydrogen at Near Zero Gravitation

The results of investigations of the evolution of the shape of the equipotentially charged surface of a liquid hydrogen layer in the external electric field in the case when the effective gravitation acceleration is near to zero are presented. The reconstruction phenomenon—the formation of a solitary wave at the flat charged surface of liquid hydrogen at some critical value of the external electric field—has been studied under the conditions of a total screening of the electric field in the bulk of a liquid by a surface charge. From the results obtained it follows that the transition of the flat surface into the reconstructed state is close to a second order phase transition. A voltage-temperature U–T phase diagram of the charged surface has been determined. The statement of a soft character of the transition has been confirmed also by the results of studies of the oscillations spectrum of the charged surface in electric fields lower and higher the critical value.     

Optimization of the processes of treatment of materials with supplementation of the definition of unknown random initial characteristics

Consideration is given to the issues of optimization of the processes of treatment of materials with certain unknown initial characteristics. Supplementing of the definition of these unknown parameters can be considered as adaptation of a mathematical model.     

Preparation of SrFe<Subscript>12</Subscript>O<Subscript>19</Subscript> · 6SrB<Subscript>2</Subscript>O<Subscript>4</Subscript> magnetic composites by spray pyrolysis

Spray pyrolysis has been used to produce X-ray amorphous precursors with the nominal composition SrFe₁₂O₁₉ · 6SrB₂O₄ in the form of spherical particles 0.3 to 2 μm in diameter. Heat treatment of the precursors at temperatures from 650 to 900°C has produced platelike strontium hexaferrite particles embedded in a SrB₂O₄ matrix. With increasing annealing temperature, the average dimensions of the hexaferrite particles increase from 80 × 20 to 450 × 100 nm and the coercivity of the material rises from 240 to 440 kA/m.