Structure and Magnetic Properties of WC–50% Co Model Alloys Containing TaC Additives

Abstract

The structure and magnetic properties of model high-cobalt WC–50% Co alloys with different carbon contents and TaC additions in the amount of 1.6–5.6 wt % are studied. Model alloys are fabricated by the liquid-phase sintering of powder mixtures at 1420°C, and their composition is described by the formula 50% Co + 50% WC + x% TaC + y% C, where x = 0, 1.6, 2.6, 3.6, 4.6, and 5.6 wt %; y = 0, 0.2, and 0.5 wt %. It is shown that precipitations of the (Ta,W)C phase are present in all studied alloys and (Ta,W)C precipitations are needle-shaped at a TaC concentration up to 3.6 wt %, while the (Ta,W)C grains become spherical at =3.6 wt %. The (Ta,W)C precipitations are arranged both in a binding phase and along the WC grain boundaries. The lattice parameter of the (Ta,W)C phase in alloys with a low carbon content lies in a range from 0.4438 nm for the alloy with 1.6% TaC to 0.4451 nm for the alloy with 4.6% TaC. It is established by the EDX analysis that the concentration of dissolved tungsten in a cobalt phase is independent of the TaC content and strongly depends on the total carbon content; it is 7, 12, and 17 wt % for alloys with high, elevated, and low carbon contents, respectively. The TaC addition in alloys with a low and elevated carbon content leads to an increase in the coercive force up to 875 A/m and a decrease in the magnetic saturation by 5–10 G m³/g. The experimental results made it possible to put forward a hypothesis on the possibility of formation of dispersed tantalum-containing precipitates in a binder phase.