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 at thermodynamic temperatures of 1023, 1123, and 1223 K in vacuum with an initial impact velocity of 6.4 m/sec was studied. Based on the experimental data and calculated elastic properties of the samples and the impact machine with a trial and error method, computational modeling of the densification dynamics was carried out using the third-order dynamic system in combination with the rheological model of Maxwell’s viscoelastic body, and previously unknown values of shear viscosity for 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 cermet samples. Part of the energy dissipated in the environment after the rebound of the machine impact parts. At the initial stage, the movement of the system is nonperiodic (atemporal) damping at high ratios between the system stiffness and viscous resistance of the cermet samples. As the ratio decreases, the movement transforms to 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, indicating the dislocation mechanism of its viscous flow. The samples produced by impact assisted sintering showed significantly higher strength values compared to the samples sintered without pressure at a higher temperature.