Segregation of Vanadium at the WC/Co Interface in VC-doped WC-Co
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Segregation of vanadium at the WC/Co interface in VC-doped WC-Co A. Jaroenworaluck, T. Yamamoto, Y. Ikuhara, and T. Sakuma Department of Materials Science, Faculty of Engineering, The University of Tokyo, 7-3-1, Bunkyo-ku, Tokyo 113-8656, Japan
T. Taniuchi, K. Okada, and T. Tanase Tsukuba Plant, Mitsubishi Materials Corp., 1511 Furumagi, Ishige-machi, Yuuki-gun, Ibaraki 300-2795, Japan (Received 8 December 1997; accepted 20 May 1998)
Morphology of carbide grain in WC–12 wt. % Co–0.5 wt. % VC was examined by HREM and EDS with a special interest in the segregation of V at the WC/Co interfaces. A small addition of VC in WC-Co is effective to suppress the grain growth of carbide grains. HREM observation revealed that the WC/Co interfaces are faceted and consist of mainly two kinds of habit planes, (1010) and (0001), respectively. EDS analyses clearly showed the segregation of doped V along the interfaces. In addition, the concentration of segregated V is higher at the (0001) type habit plane than (1010) one. The retardation of the grain growth of carbide grains in the VC-doped WC-Co is closely related to the formation of the faceted WC/Co interface.
WC-Co cemented carbide has been used as the materials for cutting tools and drills since it possesses high hardness and wear resistance.1–7 The mechanical properties of the cemented carbide strongly depend on the size of carbide grains, which is controlled to be as small as possible.2–7 It is well known that the doping of a small amount of transition metal carbide is effective to suppress the grain growth of carbide grains in WC-Co cemented carbide. Among the transition metal carbides, VC is reported to be one of the most effective dopants to obtain the small carbide grains.2–7 There have been several reports concerning the mechanism of grain size reduction in VC-doped WC-Co. They suggested that the reduction of the grain size is likely to be related to the segregation of doped VC at WC/Co2,3 or WC/WC3 interfaces. However, clear and direct evidence for the segregation of VC at the interfaces has not been reported yet. Microstructural examination, especially at the atomic scale, is needed to get a full understanding of the role of the VC dopant. In this study, microstructural analysis was performed for VC-doped WC-Co by high resolution electron microscopy (HREM) and energy dispersive x-ray spectroscopy (EDS) with a high spatial resolution. WC–12 wt. % Co–0.5 wt. % VC cemented carbide was fabricated using the raw powders, WC (Japan New Metal, 0.8 mm of mean grain size), Co (UM, 1.2 mm), and VC (Starck, 1.6 mm). The powders were wet-mixed 2450
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 9, Sep 1998
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in an attritor mill for 2 h. The slurry was dried, sieved, and pressed at 150 MPa in a shape of 16 3 16 3 5 mm. Then, the green body was heated to 1380 ±C and held for 1 h in vacuum. WC–12 wt. % Co without VC-doping was also fabricated by the same process as a reference. The samples for TEM ob
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