Production and Characterization of WC-Reinforced Co-Based Superalloy Matrix Composites
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ODUCTION
SUPERALLOYS are developed to be used in service conditions at high temperatures usually requiring high surface stability and mechanical strength. It is possible to classify superalloys into three main groups as iron-based, nickel-based, and cobalt-based.[1] Due to their high strength, corrosion resistance and hardness, superalloys get attention for applications requiring wear resistance.[2] Stellite alloys demonstrating outstanding mechanical and tribological characteristics along with outstanding corrosion and oxidation resistance at both room temperature and at high temperatures[3] have an important place among Co-based superalloys.[4] The first Stellite alloy is Stellite 6 developed by Elwood Haynes in the beginning of the 1900s.[5,6] While Co-based superalloys are traditionally present primarily in applications for the nuclear industry,[7] the use of Stellite alloys has been spreading to different industrial fields in recent times. Examples include fields such as petrol and gas processing, the medicine industry and _ O¨ZGU¨R O¨ZGU¨N and ILYAS DINLER are with the Mechanical Engineering Department, Faculty of Engineering and Architecture, Bingol University, 12000, Bingol, Turkey. Contact e-mail: oozgun@ bingol.edu.tr Manuscript submitted August 2, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
chemical processing, wood pulp, and paper processing.[8] While industrial demands make the usage area of Stellite 6 alloys participate in applications with higher stress, on one hand, production processes are tried to be adapted for the purpose of providing the needed tribomechanical characteristics.[9,10] On the other hand, it is attempted to improve the microstructural and mechanical characteristics of the Stellite 6 alloy nominal composition of which is Co-28Cr-4W-1.1C (wt pct) with element additions.[11,12] In these studies, it was reported that the microstructure and the hardness of the Stellite 6 alloy could be changed and adapted for specific applications.[5,12] Characteristics of Stellite alloys are determined by their chemical compositions to a large extent.[13] In these alloys, carbides constitute the main strengthening mechanism.[13,14] While the main strengthening mechanism is constituted by carbides, elements such as Ta, Nb, Cr, W, and Mo contribute to strength by providing solid solution hardening.[13,14] As all of these elements are also carbide-forming elements, their activity on solid solution hardening depends on the carbon content of the alloy.[2] While many kinds of carbides enhance tribocorrosion and mechanical characteristics, presence of carbon in Stellite alloys brings along a series of negativities.[3] Examples of these negativities include formation of undesired intermetallic and/or carbide compounds,[15,16] oxidation, transformation, and the
non-homogenous dispersion of the carbides.[17] While the type, size, shape, and dispersion of carbides affect the characteristics of Stellite alloys strongly,[18] unfortunately, it is not easy to predict or control the characteristics of the carbides l
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