STRUCTURE AND MAGNETIC PROPERTIES OF WC–50%Cо MODEL ALLOYS CONTAINING TaC ADDITIVES

Abstract

The structure and magnetic properties of model high-cobalt WC–50%Co alloys with different carbon content and 1,6–5,6 wt.% TaC additives are studied. Model alloys are obtained by liquid-phase sintering of powder mixtures at 1420 °C, and their composition is described by the formula: 50%Co + 50%WC + xTaC + yC, where x = 0; 1,6; 2,6; 3,6; 4,6; 5,6 wt.%, y = 0; 0,2; 0,5 wt.%. It is shown that (Ta,W)C phase precipitates are present in all the investigated alloys, whereby at up to 3,6 wt.% TaC concentration the (Ta,W)C grains have a needle shape, and at ³3,6 wt.% TaC concentration the shape of the (Ta,W)C grains becomes spherical. (Ta,W)C phase precipitates are located both in the Co-binder and along the WC grain boundaries. The (Ta,W)C phase lattice parameter in low-carbon alloys lies in the range from 0,4438 nm for the 1,6 % TaC alloy up to 0,4451 nm for the 4,6 % TaC alloy. According to EDX analysis, the concentration of dissolved tungsten in the cobalt phase is independent of the TaC content and strongly depends on the total carbon content, and for alloys with high, elevated and low carbon content it is 7, 12 and 17 wt.%, respectively. TaC addition in alloys with a low and elevated carbon content leads to an increase in coercive force by 875 A/m and a decrease in magnetic saturation by 5–10 Gs·m3/g. The experimental results allowed putting forward a hypothesis about the possibility of forming dispersed tantalumcontaining precipitates in the binder phase.