Structure and properties of coarse-grained WC-Со hard metals with extra homogeneous microstructure

Abstract

The structure and properties of coarse-grained WC-6%Co hard metals with carbon deficiency from 0,11 to 1,31 % obtained from narrow fraction tungsten carbide powder with a grain size of 5 to 15 pm were studied with respect to the stoichiometric ratio. According to the results of metallographic analysis, 1390 to 1420 °C sintering temperatures provide a non-porous alloy state with normal carbon content, while alloys with lower carbon content feature considerable porosity. It is found that hard metals with less than 0,02 % residual porosity can be obtained at sintering temperatures of 1450-1475 ° С regardless of the carbon content. It is shown that alloys with 0,11—0,91 % carbon deficiency have a two-phase structure, while the alloy with 1,31 % carbon deficiency contains n phase inclusions in addition to WC and γ phase. It is determined that lower carbon content slows down the tungsten carbide grain growth process during liquid-phase sintering. EDX analysis was used to determine the concentration of tungsten dissolved in the binder phase — 10, 12, 15 and 19 wt.% for hard metals with normal, low, medium and high carbon deficiency, respectively. Narrow fraction WC powders allow obtaining hard metals with rounded grains having a form factor of about 0,77. The alloy with 0,91 % carbon deficiency with respect to the stoichiometric ratio had the best combination of hardness and toughness (11,1 GPa and 16,0 MPa-m 1/2 ).