The wave densification in high-voltage consolidation of powder materials

Abstract The densification of conductive powders by high-voltage electric discharge consolidation (HVEDC) is studied. HVEDC method includes a simultaneous exposure of a powder sample to mechanical pressure (50–500 MPa) and to a short (less than 300 ms) high-voltage (above 1 kV) electric discharge with the current pulse amplitude of a few hundred kA/cm2. It is important the right choice of the values of the applied pressure and the parameters of the current pulses (amplitude, and time-on). The densification kinetics of an industrial iron powder is analysed by ultrarapid video-monitoring under different amplitudes of the high current pulse and pressure. It was found that the high current pulse affects the powder before the movement of the punches–electrodes. The integral temperature of the sample has a maximum value at the beginning of the densification process. The compaction process lasts less than 16 ms for all the values of the parameters studied. The shortness of the densification process in comparison with the cooling of the sample provides a constant temperature throughout the entire compaction process. The consolidation process occurs at a constant speed of the punches until they stop. Values of the constant velocity of the punches vary in the experiments from 0.5 to 2 m/c. Under a constant pressure, the experimental results show an increase in both the densification rate and of the final density of the consolidated material for the increasing current pulse amplitude up to a certain value. For a current density exceeding a critical limit value, which depends on the properties of the powder and on the applied pressure, the loss of stability of the densification process and the formation of an inhomogeneous structure of the consolidated samples are observed. Based on the analysis of the obtained experimental results, a mathematical model of high compaction of a powder material under HVEDC is formulated. The constitutive equation of a consolidated material accounts for the plastic flow of the powder particles and for the collapse of the interparticle pores. The numerical simulation results revealed optimal values of the dimensionless parameters determining the HVEDC process.