Microstructure and mechanical properties of WC-40Co composite obtained by impact sintering in solid state

Abstract

The influence of the densification temperature on the density, microstructure, mechanical properties, resistivity and coercivity of WC- 40 wt%Co composite produced by impact sintering has been investigated. The studied material possessed a 54% volume content of cobalt and tungsten carbide particles of initial size 1–3 μm. Impact sintering was carried out in a vacuum of 0.013 Pa in a temperature range covering both the solid and the liquid state: 1150, 1200, 1250 and 1290 °C.The samples were held isothermally for 20 min before consolidation and the time of the impact consolidation was 0.003–0.006 s. For comparison conventional liquid-phase sintering of samples was carried out at 1340 °C for a period of 30 min. The results showed that the impact sintering in the solid state temperature range enabled almost pore-free samples with high mechanical properties to be obtained. In particular, the samples that were impact sintered at 1200 °C have the following mechanical properties: transverse rupture strength (TRS) 3116 ± 156 MPa, fracture toughness 30.3 ± 1.2 MPam1/2, compression strength 3095 ± 106 MPa, proof stress at compression 1682 ± 82 MPa, plastic deformation at compression 11.9 ± 1.3%, strain energy density 302 ± 35 J/cm3 and Vickers hardness 7.7 GPa. The maximum TRS = 3143 ± 63 MPa and the maximum plastic deformation at compression 12.3 ± 1.1% have the samples obtained at the impact sintering temperature of 1250 °C. The impact sintering of samples at 1290 °C leads to decrease in TRS, hardness, compressive strength and proof stress at compression. The second halves of the samples were subjected to annealing at 1250 °C within 180 min after sintering. Additional annealing of the impact sintered samples led to significant changes in specific resistivity and coercivity, increased the fracture toughness, but had negligible influence on the TRS. The compressive strength and plastic deformation decreased after annealing.