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ABSTRACT
The nano-crystalline rare earth doped WC/Co powder was prepared by high energy ball milling. The nano-crystalline powders were characterized by means of XRD (x-ray diffraction), SEM (scanning electron microscope) and DTA (differential thermal analysis). The results show that adding trace rare earth elements into carbides is effective to minish the grain size of WC/Co powder. The grain size of rare earth doped powder became two times smaller as compared with the undoped powder within ball milling times of 25-45 hours. The XRD peak of Co phase disappeared after 25 hours ball milling. A sharp peak of heat release at the temperature of 597°C was emerged in DTA curve within the range of heating temperature. After consolidated the rare earth doped WC/Co alloy by high energy ball milling exhibits ultra-fine grain sizes and better mechanical properties.
Keywords: cemented carbide, nano-crystalline powder, rare earth, high energy ball milling
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1 Introduction
Nanostructured WC-Co alloys are one of the important materials used in high precision and microfabrication machining. Presently, the use of nano-crystalline WC powders for producing WC-Co materials with finer microstructures represents one of the most active fields of research in the hardmetal industry, because the nanostructured WC-Co alloys possess excellent mechanical properties such as high hardness, strength and toughness. Although ultra-fine WC-Co powders have been developed by thermochemical and thermomechanical process named as spray conversion process (SCP) or high energy ball milling, since nano-crystalline powders are the most reactive ones, higher specific surface areas enhance sintering activity, the WC grain growth behavior is not easy to be properly controlled during the sintering. Some attempts were made to control the grain growth behavior by Microwave Sintering (MS), Spark Plasma Sintering (SPS), Hot Isostatic Press (HIP), and by adding some grain growth inhibitors into the powders using high energy ball milling[1-3]. The mechanical properties can be improved by adding trace rare earth elements into cemented carbides, which either creates oxide dispersion strengthened effectiveness or inhibits the WC grain growth during sintering, so that the lifetime of the products can be prolonged[4-7]. The effectiveness of the inhibitors is correlative with the composition, content and adding procedure. Therefore, it is important to research and develop the nano-structure rare earth doped cemented carbides materials[8-10].
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