COMPACTION DYNAMICS OF FINE-GRAINED WC + 25 wt.% Co CERMET DURING LOW-TEMPERATURE IMPACT SINTERING IN VACUUM

Abstract

The compaction of the fine-grained tungsten carbide-based cermet with a 25 wt.% cobalt binder during impact sintering at 1150, 1200, 1250, and 1300 °С with an initial impact velocity of 5.8 and 6.2 m/sec with the initial solid-phase state of the binder is investigated. Based on the obtained experimental data and the calculated elastic properties of the samples and the impact machine, the modeling of compaction dy-namics using a third-order dynamic system is carried out by hit-and-miss method and the value of shear viscosity of the cermet matrix determining the energy dissipation in the system and the irreversibility of the material compaction is obtained. In addition, the data on (i) the phase trajectory of the dynamic system motion, (ii) the duration of impact loading, (iii) the time dependences of the force, compression, velocity, and acceleration of the system, (iv) compaction work, (v) and the mechanical–thermal effect resulting from the energy dissipation and causing a significant increase in the temperature of cermet porous samples are obtained. This temperature increase, at the starting temperature of the samples close to that of eutectic formation and low starting porosity of the samples, can cause the liquid phase to squeezed out of the sample volume into a porous graphite shell that protects the samples against adhesion to the metal die. The estimated activation energy of the viscous flow of the matrix forming the porous cermet is 1.1 eV or 103 kJ/mol.