超粗晶硬质合金的显微结构和力学性能

Microstructure and mechanical properties of extra coarse grained cemented carbides

以超粗碳化钨粉和球形钴粉为原料,通过真空液相烧结工艺制备钴含量分别为7%和10%(质量分数)的超粗晶硬质合金。利用光学显微镜和SEM观察并研究超粗晶硬质合金的显微结构;测定并计算材料力学性能与显微组织参量间的关系。结果表明:超粗晶硬质合金中WC晶粒呈圆角形或等轴形,分布均匀;临界裂纹长度与WC平均晶粒度相近,导致横向抗弯强度降低;圆角形WC晶粒和较大粘结相平均自由程的存在使裂纹产生偏转、分叉和不连续现象,提高了材料的断裂韧性。

The extra coarse grained cemented carbides with Co contents of 7% and 10% （mass fraction） were prepared by vacuum liquid phase sintering with extra coarse WC and spherical cobalt powders used as starting materials. The metallic phases and microstructure of these cemented carbides were observed by optical microscope （OM） and field-emission scanning electron microscope （FESEM）, respectively. The mechanical properties of extra coarse grained cemented carbides and the correlations between mechanical properties and microstructure parameters were studied. The results show that most extra coarse WC grains are rounded or equiaxed, and the contiguity of WC decreases slightly with the WC grain size increasing. The calculated critical crack lengths are almost similar to extra coarse WC grain sizes, which leads to poor transverse rupture strengths （TRS） of the extra coarse grained cemented carbides. The extra coarse rounded WC grains and thick cobalt interlayers lead to the appearance of bifurcating, diverging and discontinuous cracks and contribute to the enhancement of rupture toughness of cemented carbides.