Effect of sintering temperature on Microstructure of double crystal cemented carbide

The grain size of tungsten powder can affect the grain size and properties of cemented carbide. The hardness of cemented carbide can be improved by refining the grain size of tungsten powder. In this experiment, W-Co alloy with different thickness was used as the research system, and a small amount of tantalum was added to sinter at different temperatures. The effect of sintering temperature on the microstructure of double crystal cemented carbide is as follows：

When sintered at 1425 ℃, the average grain size is 0.91 μ m. The standard deviation was 0.36 μ m；

The average grain size is 0.75 at 1450 ℃ μ m. The standard deviation was 0.33 μ m；

When sintered at 1500 ℃, the average grain size is 0.98 μ m. The standard deviation was 0.42 μ m。

When sintered at 1425 ℃, the grain size is mainly distributed in the very fine grain, which is basically normal distribution; When sintered at 1450 ℃, the grain size is mainly distributed in the adjacent ultra-fine and ultra-fine grains, the sum of which accounts for nearly 70% of the total number of statistics, and the number of nanocrystals also reaches the highest; When sintered at 1500 ℃, the grain size is mainly distributed in the very fine grains, but some grains grow up obviously, and a few coarse grains appear, which leads to the decrease of the proportion of nanocrystals and ultrafine grains, while the proportion of medium and coarse grains increases, and the grain size distribution is relatively dispersed.

The grain size of tungsten does not increase with the increase of sintering temperature. When sintered at 1450 ℃, the grain size of tungsten decreases, which is mainly related to the inhibition of tantalum. The solubility of tungsten in the binder phase can be reduced by dissolving the inhibitor in the binder phase. When sintering at 1425 ℃, the solubility of tantalum in cobalt is not large and the inhibition effect is not obvious due to the low temperature; When sintered at 1450 ℃, the eutectic temperature of tantalum in cobalt is reached, the solubility of tantalum in cobalt is increased, and the inhibition of tungsten is enhanced; With the increase of temperature, the solubility of tantalum in cobalt will not continue to increase, and the inhibition effect remains unchanged. High temperature is conducive to the growth of tungsten grains. Therefore, tungsten grains continue to grow when sintered at 1500 ℃.