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WC/Co Interface Structure in Cemented Carbides doped with VC, NbC and ZrC T. Yamamoto 1,2 , I. Sugiyama 1 , Y. Yamanaka 1* , T. Taniuchi 3 , F. Shirase 3 , T. Tanase 4 and Y. Ikuhara 2,5 1 Department of Advanced Materials Science, The University of Tokyo, Kashiwa, 277-8565, Japan 2 Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya, 456-8587, Japan 3 Tsukuba Plant, Mitsubishi Materials Corporation, Ibaraki, 300-2795, Japan 4 JAPAN NEW METALS Co.,Ltd., Toyonaka, 561-0829, Japan 5 Institute of Engineering Innovation, The University of Tokyo, Tokyo, 112-8656, Japan * Present affiliation, Analysis & Physical Properties Centers, Showa Denko, Chiba, 267-0056, Japan WC-Co based cemented carbides are very useful hard materials that are widely used for mechanical machining tools, wear resistant applications and so on[1]. The cemented carbides have a composite structure that hard WC grains are bound byγ -phase of Co-based metallic phase, which is very suitable to exhibit a high performance for mechanical machining tools. The strength of the cemented carbides depends on WC grain size so that it is important to suppress WC grain growth during sintering. For this purpose, other carbides are often doped as inhibitors. VC is a typical carbide to obtain fine grained cemented carbides. According to previous reports, the doping of VC largely changes the interface structure at WC/Co to form micro facet structure like stairs consisting of two habits of {101 _ 0} and (0001)[2]. The interface structural change is closely related to V segregation at the interface. Segregated V strongly retards a step migration on the surfaces of WC grains, which results in the grain growth inhibition. In practical cemented carbides, other carbides in addition with VC are often used, however, there are few reports about the effects of such carbides on the interface structure. In this study, we selected three type carbides of VC, NbC and ZrC from a viewpoint of their inhibition effects. The interface structures and segregation behaviors were investigated by high-resolution electron microscopy. The cemented carbides used in this study are WC-12mass%Co, WC-12mass%-0.5mass%NbC, and WC-12mass%-0.5mass%ZrC with middle carbon content. As for VC-doped alloys, the amount of VC was changed from 0.1-0.5mass%. Sintering was conducted at 1380℃ for 1h in vacuum and cooled down to room temperature by introducing He gas into a furnace. The effectiveness of other carbides on WC grain size was confirmed to be VC>NbC>ZrC [3] as shown in Fig. 1. Especially, a grain size does not change in ZrC-doped carbide. Fig. 2 shows HRTEM images taken from the respective doped carbides. In VC-doped carbide, microfacets are formed at WC/Co interfaces, which is very similar to that previously reported[2]. On the other hand, the other two doped-carbides do not exhibit a particular interface structure, however, the interface in ZrC doped carbide tends to show a more round shape at the corners of the two habits as shown in Fig. 2(c), comparing those of NbC-doped carbide. The segregation behavior at the interface was found to change among the three doped-carbides. Fig. 3 shows EDS profiles taken at interfaces of the three doped-carbides. As stated before, doped V strongly segregated at the interface as shown in Fig. 3(a). In case of NbC-doped carbide, © 2010 Japan Fine Ceramics Center AMTC Letters Vol. 2 (2010) 56
