WC晶粒度不同的双层硬质合金中的梯度结构

Gradient structure of coupled cemented carbides with different WC grades

以晶粒度不同的2种WC粉末为原料,制备双层硬质合金试样。研究结果表明在试样的层界面附近,出现过渡显微组织,其WC晶粒度、硬度呈现梯度分布,细晶层一侧的WC晶粒粗化,Co相平均自由程增大,硬度下降;粗晶层一侧的硬度上升;合金两侧的WC颗粒均处于非平衡状态。液相烧结时,界面两侧都有从外界吸入液态钴相以便使WC颗粒达到平衡状态的趋势,由于溶解-析出机制的作用,细晶侧的WC颗粒溶解后通过界面在粗晶侧的WC颗粒上析出,从而使粗晶侧的WC长大并达到平衡状态;与粗晶侧的WC相比,细晶侧的WC颗粒处于更加不稳定的状态,因此,粗晶侧的液态钴相流向细晶侧,使细晶侧的WC骨架发生重组而达到稳定状态。

Cemented carbides with gradient structure was fabricated by coupling WC grades with different grain sizes. The results show that the gradient structure is formed at the interface of the coupled cemented carbide, and also the hardness and grain size of WC are varied gradiently at the interface. At one side of the cemented carbide with fine WC, WC grain grows up obviously, the mean free path of binder phase increases and the hardness decreases; however, the hardness increases at the side of the sample with coarse WC grain. The reason may be that the liquid binder phase is driven from the side of coarse WC to the side of the sample with fine WC grain size due to the difference of the driven force, which is the results of solution/precipitation mechanism during the process of liquid sintering.