Effects of WC content on core/rim phases and microstructure of TiB2-TiC-WC-(Co-Ni) cermets

Abstract The TiB2-(40-x)TiC-xWC-(Co-Ni) (x = 0, 5, 10, 15, 20, 25) system cermets were prepared by powder metallurgy method. The variations in phase constituents, microstructure, particle and core size, rim composition after sintering were characterized by XRD, SEM-BSE, FIB-SEM(CBS), EPMA, Image J software and TEM/EDS. The results show that the TiB2-35TiC-5WC-(Co-Ni) cermet has typical core/rim structure with inner/outer rims. The diameters of cores are less than 1 μm. These fine cores are mainly TiC, but also have a small amount of TiB2. When the content of WC increased to more than 10 wt%, most of the fine TiC core/rim structure disappear, but the coarse TiB2 core/rim structure of about 4 μm appear. The inner rim phase is mainly (Ti, W)C solid solution for typical fine core/rim structure, however the inner rim phase is (Ti, W)(B, C) solid solution for the coarse-core/rim structure. As WC content increasing to 15 wt%, the thickness of inner rim increase and the contrast between inner rim and outer rim disappear, and only inner rim can be observed, meanwhile the volume fraction of binder phase increasing. The phase structures of TiB2, rim and binder phase are identified by XRD. The grain size of core/rim are analyzed.