Cobalt Content and Tungsten Carbide Grain Size

1 Cobalt Content and Tungsten Carbide Grain Size 

As a result, by selecting appropriate combinations of cobalt contents and carbide grain sizes, the hardness of WC-Co can be varied from below 800 HV to more than 2000 HV. The most appropriate combination is determined by the properties which, besides hardness, are required for a specific application. The recent introduction of grain sizes of the order of 10 nm has extended the range of possible hardness well above 2000 HV [16]. However, nano-grade hardmetals are not included in the present review because they always contain grain refiners such as VC or Cr2C3, while this review is limited to two-phase V/C- Co alloys. 

Lee and Gurland [8] attempted to express the relationship that exists between the hardness of WC-Co, its microstructure and its composition by using a simple law of mixtures of the type 

By replacing F c Eq. (3) with Fc, Lee and Gurland obtained the following equation  

By using Eq. (5) it is possible to calculate that in commercial WC-Co grades (i.e. grades with cobalt content ranging from about 6 to about 20 weight-%) the first term of the equation accounts for up to 80% of i/wc-co. which means that the continuous carbide volume accounts for up to 80% of the hardness of the alloy. 

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