Densification Dynamics of WC–36 wt.% Cu Cermet During Impact Assisted Sintering in Vacuum

Abstract

The densification of a fine-grained tungsten carbide cermet containing 36 wt.% copper binder during impact assisted sintering in a vacuum at thermodynamic temperatures of 1023, 1123, and 1223 K with an initial impact velocity of 6.4 m/s was studied. Based on the experimental data and calculated elastic properties of the samples and the impact machine, computational modeling of the densification dynamics with a trial and error method was carried out using a third-order dynamic system in combination with the rheological model of Maxwell’s viscoelastic body, and as a result previously unknown values of shear viscosity for material cermet matrices were obtained. The time dependences of force, compression, velocity, and acceleration of the system, as well as shrinkage, root-mean-square stress, and strain rate, of the cermet samples during impact assisted sintering were determined. The calculated phase trajectory of the dynamic system movement showed that the initial kinetic energy of the impact was not completely exhausted for the irreversible densification of the cermet samples. Part of the energy dissipated in the environment after the rebound of the machine’s impact parts. At the initial stage, the system exhibited nonperiodic (atemporal) damping during its movement at high ratios between the system’s stiffness and the cermet samples’ viscous resistance. As the ratio decreased, the movement transformed into damping oscillations. The work of densification and the thermomechanical effect, which significantly increased the temperature of porous samples, were evaluated. The estimated activation energy of the viscous flow for the porous cermet matrix was 0.34 eV or 33 kJ/mol that indicated the dislocation mechanism of sintering. The samples produced by impact assisted sintering showed significantly higher strength values compared to pressureless sintered samples at a higher temperature.