Densification Dynamics of Fine-Grained WC+25 wt.% Co Cermet During Low-Temperature Impact Sintering in Vacuum

摘要

The densification of fine-grained tungsten carbide-based cermet with 25 wt.% cobalt binder during impact sintering at 1150, 1200, 1250, and 1300A degrees C with the initial impact velocity of 5.8 and 6.2 m/s, 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 simulation of densification dynamics using third-order dynamic system is carried out by hit-and-miss method and the value of the shear viscosity of cermet matrix determining the energy dissipation in the system and the irreversibility of the material densification are obtained. In addition, the data on the phase trajectory of the dynamic system motion, the duration of impact loading, the time variations of the force, compression, velocity, and acceleration of the system, densification work, and the mechanical-thermal effect resulting from the energy dissipation and causing a significant increase in the temperature of the porous cermet samples are obtained. At the starting temperature of the samples close to that of eutectic formation and low starting porosity of the samples, this temperature increase can cause the liquid phase squeezing from the sample volume into the 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.