Reactive electric-discharge sintering of TiN-TiB2

Powder mixtures based on titanium and its dihydrides are sintered by electric discharge in a certain current mode to produce TiN + TiB₂ composites. It is established that the use of tetragonal titanium hydride as the starting material results in the complete synthesis leading to a TiN + TiB₂ composite. The higher shrinkage rate results from the higher purity of titanium dihydride, which, in its turn, increases the partial pressure of hydrogen in the reaction area and the reaction rate. Tetragonal titanium hydride is more preferable than cubic hydride and metal titanium. The microstructure of alloys resulting from the sintering of hydride-based mixtures is more homogenous: it includes equiaxial grains with the mean size of about 1 µm.     

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.     

Comparison of diffusion calculations for two models of powder mixtures

Summary The advantages and drawbacks are discussed of two models of powder mixtures: The model based on single-particle approximation and the concentric sphere model. Calculated values obtained by using both models are compared with experimental data.Translated from Poroshkovaya Metallurgiya, No. 1, pp. 23–24, January, 1968.     

Correlation between the structure and heat treatment of powder particles

Conclusions It has been established that nickel (carbonyl), copper, iron, titanium, and zinc powders reflect light according to laws close to those of diffuse reflection; the intensity of reflection from annealed powders is greater than that from unannealed powders.In an optical investigation of zinc powder (at an angle of incidence of 60° to a plane specimen), reflection of a mixed type is observed. The maximum found in the region of an observation angle of 60° indicates the existence of a mirror component in the reflected light energy.A parallel study of the defectiveness of powders based on measuring the broadening of x-ray diffraction lines demonstrated that the two types of defectiveness (surface and volume) can change either in conformity with or independently of each other.Translated from Poroshkovaya Metallurgiya, No. 10 (82), pp. 12–16, October, 1969.     

Influence of specific energy expenditures in electric-discharge sintering on the structure and properties of a copper-tin-abrasive composite

Conclusions It has been experimentally established that an increase in the specific energy expenditure caused by an increase in the strength of the dc leads to an increase in process temperature in electric discharge sintering of a copper-tin-abrasive composite. By changing the specific energy consumption parts with different structures and properties are obtained from this composite by electric discharge sintering.Translated from Poroshkovaya Metallurgiya, No. 8(284), pp. 67–70, August, 1986.     

Effect of the degree of oxidation on the structure and properties of material obtained by electric sintering of powdered swarf of aluminum bronze

Conclusions A characteristic feature of specimens of powdered swarf of aluminum bronze sintered by an electric current is the existence of interparticular contacts of films containing copper, aluminum, and iron oxides.The process of capture of particles is substantially affected by the state of their surface. In the zone of contact there occur complex physicochemical phenomena due to the simultaneous destruction (as a result of electrical breakdown, thermal dissociation of oxides, additional deformation of particles) and renewed partial restoration of oxide films. In some places there is not enough time for films to originate again. On account of that physical contact is established between the contiguous surfaces of the particles.As a result of the disappearance or reduction of the amount of interparticular oxides in specimens sintered by electric current, electrical resistance decreases and the strength of the material increases.Translated from Poroshkovaya Metallurgiya, No. 10(298), pp. 44–48, October, 1987.     

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.