Experimental Study and Percolation Model of Compactified Metallic Mixtures Sintering by Electrical Discharge
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MODEL OF COMPACTIFIED AND PERCOLATION EXPERIMENTAL STUDY DISCHARGE. SINT;§ING BY ELECTRICAL METALLIC _MIXTURES , A.K.Sarychev , A.P.Vinogradov ,B.P.Peregood O.B.Pakhomov of Academy Temperatures,USSR of High Institute Science,Izhorskaya 13/19, Moscow,127412, USSR A.F.Ioffe Physical Technical Institute, USSR Academy of Sciences, Polytechnicheskaya 26, Leningrad,194021,USSR 1.Introduction use for compaction of Different ways of pulsed current conducting materials have been studied during recent years, of powder problems with technological mainly in connection metallurgy. As a rule, the current is driven through a blank placed in a mould under external pressure [1-6]. Pulsed current partial or complete action on a blank may lead to either melting of granules [1,2], to the heating of granules and their and plasticity increase [3], to the destruction of oxide films granules surface activation [4,5] and to the break-down and sintering of chains forming channels in the direction of current [6]. In this paper electric pulse strengthening of pressed metallic blanks due to plastic welding of granules by thermoelastic stresses appearing with Joule heat release at granule boundaries are investigated. Experimental data and theoretical methods used in the paper, as well as the qualitative results, are of sufficiently general nature.Experiments were held with models of consumable electrodes used in vacuum electric arc melting of titanium [8]. The electrodes are manufactured by the method of semicontinieous pressing out of granules of irregular shape. Titanium sponge pieces with characteristic size about 0.5 cm constitute the principal fraction of the primary blend. Titanium scrap and doping admixtures also enter the blend composition. A blank is shaped as a cylinder of up to 65 cm diameter and up to 550 cm length. The use of electric pulse sintering to -increase the strength of pressed consumable electrodes has been suggested in
[9,10]. 2.
Strength Growth Under Electric Current Sintering
Experimental studies were carried out with electrodes of 4 and 10 cm diameter and 25 and 30 cm length. Sintering was implemented by means of various pulse current generators on high voltage condenser banks. The duration of the current action was varied between 4ms and 16 ms with the current amplitude up to 90 KA. The change in the sample strength was detected both by
direct
measurement
of
bending
strength
and
by
electric
resistance variation. Because of the clearly pronounced structural inhomogeneity of different samples manufactured under the same press load strength has a substantial spread. Therefore as a measure of strength we took not the press
Mat. Res. Soc. Symp. Proc. Vol. 195. 01990 Materials Research Society
218
pressure, but the conductivity, that is, the easily measured parameter related in an obvious way to the mechanical properties of the considered disordered system. Both conductivity and'strength are specified by the properties of boundaries of granules pressed together. The effect of sample strength growth after th
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