Ultrafine tungsten carbide has excellent performance, but its preparation process will have more difficulties. As the growth rate of WC grain is not easy to be controlled by adjusting the sintering conditions in sintering, grain growth inhibitors are needed.

 

 

The effect of different kinds of grain growth inhibitors on ultrafine tungsten carbide is different. At the same time, the grain growth inhibitor not only affects the grain size of the cemented carbide, but also has a certain influence on its hardness and other properties.

 

Effect of different kinds of grain growth inhibitors on ultrafine tungsten carbide

It is generally believed that the inhibitory effects of various carbides are related to their thermodynamic stability. The size order of its inhibitory action of VC>Mo₂C>Cr₃C₂>NbC>TaC>TiC>ZrC = HfC. But when in solution of metal atoms are almost the same, while the effect of inhibiting grain growth in the order of VC>NbC>TaC>TiC>Mo₂C>Cr₃C₂>ZrC = HfC.

 

These relationships are generally established at the sintering temperature of 1320~1480℃. Mechanism of action of different inhibitors on the alloy is different, so the effect on the properties of the alloy is different. In order to obtain the best use of inhibitors, two or three inhibitors are usually used simultaneously.

 

Effect of grain growth inhibitors on ultrafine tungsten carbide

In addition to the inhibition of grain growth, the grain growth inhibitors also have a significant effect on the properties of the tungsten carbide. When the contents of VC and Cr₃C₂ are the same, the alloy adding VC has higher hardness but lower bending strength. As for the alloy adding VC, when the grain of WC is finer, the hardness of the alloy is higher.

 

When adding Cr₃C₂, WC particles are coarser. Due to the increase of the relative content of Cr₃C₂ solid solution in the bond phase, the average free path of bond phase in the alloy increases. As a result, the alloy has higher fracture toughness. It is found that the more the addition of VC and Cr₃C₂, the larger the grain refinement effect, and the characteristics of VC inhibition and growth are better. 

 

The density of the tungsten carbide decreases with the increase of the amount of the inhibitor, and the pores also increase obviously. The strength is reduced, and the hardness increases. The combination of hardness and strength is greatly dependent on the category and content of the inhibitor.