微观组织结构与小负荷维氏硬度
( 1. 中南大学 粉末冶金国家重点实验室， 长沙 410083；
2. 长沙矿冶研究院， 长沙 410012；
3. 中南大学 冶金科学与工程学院， 长沙 410083)
摘 要: 用光学显微镜观察了采用两步法工艺制备的双相结构功能梯度WC-Co硬质合金的微观组织结构，并测量了其小负荷维氏硬度。 结果表明： 合金芯部的η相呈点状弥散分布于硬质相WC颗粒之间和硬质相WC颗粒与Co粘结相之间； 在3相区，由于超细η相的存在， WC晶粒大部分已失去其多角特征， 出现晶粒圆化现象； DP合金前驱体在后续渗碳处理过程中， 合金表层的部分Co在碳势差的作用下向合金内部发生迁移，使合金中间过渡层及其附近区域中Co粘结相呈现梯度变化； 合金表层与合金中间过渡层在由原来的3相组织变为两相组织的同时， 合金中细小的WC晶粒明显减少， WC晶粒的均匀度明显增加； 合金截面的小负荷维氏硬度出现由高变低再由低变高的规律性变化， 与合金内部微观组织结构的变化相对应。
关键字: 硬质合金； 双相结构； 功能梯度合金； 微观组织； 维氏硬度
（ 1. State Key Laboratory of Powder Metallurgy,
Central South University, Changsha 410083, China;
2. Changsha Mining and Metallurgy Research Institute, Changsha 410012, China;
3. School of Metallurgical Science and Engineering,
Central South University, Changsha 410083, China）
Abstract: The microstructure of functionally graded WC-Co cemented carbide with dual phase structure prepared by so-called two-step technique was observed by metallography. Vickers hardness (HV2) along the gradient was tested by micro-hardness tester. The results show that the η phase in the core zone is in dispersion-distributed state, locating between WC and WC particles, and between WC particle and the binder with an average grain size less than that of WC. Because of the existence of fine η phase, most of the WC grains in the core zone loss their multi-angle character, taking a rounded appearance. During the carbonization process of the as-sintered cemented carbide with η phase in the whole body, part of cobalt in the surface zone migrates towards the inner of the alloy under the driving force of carbon-activity difference, with the formation of cobalt gradient structure and the microstructure change of the surface zone and the intermediate zone from the original WC+γ+η into WC+γ, accompanied by the remarked decrease of very small WC grains and the increase of uniformity degree of WC grains. Vickers hardness (HV2) along the gradient changes regularly from high to low, then from low to high, corresponding to the microstructure change in the alloy.
Key words: cemented carbide; dual phase structure; functionally graded material; microstructure; vickers hardness
