脱β层梯度硬质合金表层元素分布的电子探针微区分析

Electron probe micro analysis on element distribution across surface layer of graded cemented carbide with cubic carbide free layer

利用WC,Co,(Ti,W)C,Ti(C,N)等原料粉末,采用1步烧结法制备脱β层梯度硬质合金,利用扫描电镜观察合金表层的微观组织结构,采用电子探针微区分析技术(electron probe micro analysis,EPMA)定性分析合金表层的金属元素W、Ti、Co及轻元素C、N的分布规律,采用EPMA定量技术分析金属元素尤其是Co的复杂分布规律,并对其形成机制进行深入讨论。定性分析结果表明:脱β层内W元素的含量稍高于合金芯部的平均W含量;所有含Ti相均已完全脱除;脱β层不仅是缺立方相层,同时也是富Co层;脱β层中C元素的含量略有下降;N元素含量并不为零,某些区域甚至高于芯部。定量分析结果表明:脱β层中Ti元素含量基本为零,但在界面靠近芯部一侧Ti元素含量明显高于芯部的平均值;从合金表层至芯部依次存在低钴层、高钴层及贫钴层3个钴含量不同的区域。合金整个表层钴含量的复杂分布情况是由钴原子的空位扩散机制与液相迁移机制联合形成的。

Graded cemented carbide with a cubic carbide free layer（CCFL） was prepared by one-step sintering process with normal raw material powders such as WC, Co, （Ti, W）C, Ti（C,N） and so on. The microstructure in surface layer of the graded alloy was investigated by scanning electron microscopy （SEM） . The distribution profile of element W, Ti, Co, C, N across surface layer of the alloy was qualitative studied by electron probe micro analysis （EPMA）; and the distribution profile of metallic element Co especially was quantitative analyzed further by EPMA; moreover, the formation mechanism of Co distribution was discussed in detail. The results of qualitative analysis show that the content of W element in CCFL is a little higher than that in core zone; all solid solution containing Ti has decomposed and migrated from CCFL completely; the CCFL is not only a cubic carbide free layer firstly, but also a Co-enriched layer simultaneously;There is a slight downward trend for the content of C element in CCFL;and the content of N element in CCFL is not zero point as people think usually, and is even higher than that in core zone. The further results of qualitative analysis show that the content of Ti element closes to the core side is apparently higher than that of mean content in core zone although it is almost zero point in CCFL;there exist in turn three layers with different Co content from surface to core of the graded alloy： low Co layer, high Co layer and poor Co layer. The complex distribution of element Co is derived from the vacancy diffusion of Co and liquid phase migration mechanism together.