硬质合金中钴的相变及影响因素

Phase Transformation and Effect Factors of Co in Cemented Carbide

选取10%Co-WC(质量分数)硬质合金和原料钴粉试样,通过原位X射线衍射、扫描及透射电镜系统分析了钴相变温度和相变钴的组织,探讨了硬质合金中钴的相变及相变影响因素。结果显示,Co相变的晶体学取向关系为{111}α//{0002}β,<110>α//<112 0>β,在钴粉及硬质合金中,Co的晶内均存在切变相变引起的片层组织。相对于钴粉,硬质合金中的Co的As和Af分别增加约80℃,主要原因是硬质合金中WC的固溶、WxCoyCz析出、WC和Co间热膨胀差引起的拉应力,使Co相变自由能及切变阻力增大,从而增加了Co相变所需过冷度。

The phase transformation temperature, microstructure of 10 wt% Co-WC cemented carbide and pure Co powder were analyzed using in situ X-ray diffraction(XRD), scanning electron microscope(SEM) and transmission electron microscope(TEM). The phase transformation and effect factors of Co in cemented carbide were also investigated. The results show that the crystal orientation relationship of Co phase transformation is {111}α//{0002}β,<110>α//<112 0>β and lamellar structure is formed as the stacking fault induced at the {0002} crystal plane during Co phase transformation. Compared with pure Co powder, the As and Af of Co phase in cemented carbide are up about 80 ℃, which shows the supercooling degree increases. The main reasons are the W and C atoms solid solution, WxCoyCz precipitation, the thermal residual tensile stress caused by the different coefficients of thermal expansion between WC and Co, thus increasing the needed supercooling of Co phase transformation.