A. I. Raichenko

Powder sintering with application of an electric current and periodic mechanical pulses

Electric-discharge sintering of metal powders and powder composites is accompanied by anomalously high rates for compaction, and alloy and phase formation. Application of low-frequency pressure pulses on powders and powder mixtures during the concluding stage of electric-discharge sintering leads to even greater intensification of compaction and alloy formation.

Alloy Formation in a Heterogeneous System under the Action of an Electric Current

The question of a significant increase in the level of dissolution and alloying within a heterogeneous composite around a more refractory component in the presence of a liquid phase with passage of an electric current is considered. Redistribution of a substance into the depth of molten tin under the action of an electromagnetic forces is demonstrated using the system Cu – Sn as an example.

Theory of Initial Microcavity Growth in a Liquid Metal Around a Gas - Releasing Particle. Part 2. Bubble Initiation Conditions and Growth Kinetics

A theory is presented that includes capillary, hydrodynamic, and diffusion aspects. The main attention is devoted to capillary and hydrodynamic effects. The hydrodynamic process (bubble growth) is governed by a nonlinear integrodifferential equation, whose coefficients are dependent on the surface tension, density, and viscosity of the liquid, and also on the difference between the pressure in the gas within the bubble and that in the surrounding liquid. The gas pressure in the bubble is dependent on the rate of gas release from the inclusion (source). An expression is derived for the bubble radius as a function of time. The theory can be useful for developing the technology of powder materials and foam metals.

Kinetics of Electric Discharge Sintering of High-Speed Steel Powders

Electric discharge sintering of high-speed steel R6M5F3 is studied. It is shown that powder heating rate is mainly governed by the heat generated according to the Joule ― Lenz rule and compaction may be described by equations that are valid for hot pressing. A new method is described for preparing billets for tools made from high-speed steel without some of the labor-intensive and expensive operations. This method combines electric discharge powder sintering with subsequent hot extrusion.

Variation in the particle size of FE–TI–B4C powders induced by high-voltage electrical discharge

The effect of high-voltage electrical discharge (ED) on the particle size of Fe–Ti–B4C powders in a hydrocarbon liquid is studied. It is shown that high-voltage ED allows significant refinement of the powders. The important factors are integral processing energy and pressure in the discharge channel. A relationship between the integral processing energy and decrease in the average diameter of micropowder particles is found. It is shown that the average particle size monotonically decreases up to a certain value of integral processing energy. The use of high-voltage ED for the refinement of micropowders permits significant reduction in time and energy needed to reach the desired particle size compared with other methods.

Effect of Electromagnetic Field in Hard Metal Technique

The publications of the effect of electric, magnetic, or complex electromagnetic fields applied in addition to well-known conventional processing of WC–Co powder composites are analyzed. Two types of composite processing are considered: conduction and induction heat treatment. The basic properties of equipment used by techniques for processing the above composites are studied based on the existing equipment. The effect of some features of the structure of materials on their properties is analyzed. A special attention is paid to structure defects, such as cracks and the continuity of brittle (WC) and ductile (Co) phases. Their effect on the strength, wear resistance, elasticity, fracture toughness, and other properties of hard metals is considered in details. This study provides a number of recommendations for eliminating or minimizing the impact of defects on the structure and properties of powder composites.

Electric Current Activated Sintering of Porous Powder Compacts

A powder body model has been developed to study mass transfer through movement of the material as sliding blocks (packs) simulating particles and grains in polycrystals. The key model parameters are grain size and mobility of intergranular boundary layers. The theoretical analysis has resulted in mathematical relations showing that transfer of the material to fill the pores intensifies with transition to finer grains (subgrains, particles) and with higher mobility of the material in boundary layers between the grains. The boundaries between grains and particles experience greater heating during electric current sintering. Temperature in the boundary zone remains higher than the area far from the boundaries, consequently leading to greater mobility of the material. This improves intergranular slip and promotes fast and ultrafast shrinkage.

Activating Action of an Electric Current on the Penetration of Molten Metal into Surface Defects of Materials of a Diverse Nature

How liquid metal penetrates into pores and other such defects in the structure of a solid and also between graphite fibers upon passage of an electric current through a heterogeneous composite consisting of a metal/graphite-fiber material in the presence of a liquid phase has been studied. The electric current has been found to have a positive effect, i.e., it increases the penetration of molten metal into the defects in the material without need of a vacuum.

Redistribution of Extraneous Solid Particles Suspended in Molten Metal during Passage of an Electric Current

Redistribution of nickel-base heat-resistant alloy suspended in molten tin under the action of a direct electric current is studied by experiment and analyzed. It is established that there is an increase in solid particle concentration over the height and in the radial direction under the action of a current passing along the container axis. This is explained by the simultaneous effect of thermal convection and Lorentz contraction electromagnetic forces directed radially.

Theory of Initial Growth of a Microcavity in a Liquid Metal Around a Gas-Releasing Particle. Part 1. Physical and Mathematical Models

Certain inhomogeneities in a liquid can act as bubble nucleation centers. If such a center is a source of gas on a considerable scale, the bubble can grow rapidly to an appreciable size. The following model is proposed for analyzing this process: a solid sphere (compound containing a gas-forming element such as hydrogen) is surrounded by a liquid metal. The initial equations are as follows: the Navier-Stokes equation, in which there are terms containing the concentration of the gas component; the equation of continuity; and the equation for the convective diffusion of the gas component in the liquid metal. The growth of the bubble obeys an integrodifferential equation derived here, which reflects the effects of the hydrodynamic, diffusion, and capillary factors.