Abstract
Functionally gradient WC-Co composites having a Co depleted surface zone and not comprising the h phase can be manufactured via carburizing process. During carburizing, besides carburizing process parameters, the microstructural parameters of WC-Co materials, such as WC grain size and Co content, also have significant influences on the formation of Co gradient structure. In this study, the effects of WC particle size and Co content on the gradient structure within gradient hardmetals have been studied, based on a series of carburizing experiments of WC-Co materials with different WC particle sizes and cobalt contents. The results show that both the thickness and the amplitude of the gradients within gradient WC-Co materials increase with increasing initial WC particle size and Co content of WC-Co alloys. The reason for this finding is discussed.
Highlights
Due to their unique microstructure and superior combinations of wear resistance vs. fracture toughness, functionally gradient WC-Co composites with cobalt (Co) content increasing from surface to the interior of the bulk of the material have been the objective of intensive research in the hardmetal industry for a long time [1,2,3]
This technology allows the fabrication of gradient hardmetals with a very low Co content in the near surface layer, a significant disadvantage of these gradient hardmetals obtained by this approach is the presence of the very brittle core comprising much Ș-phase, which is detrimental to the mechanical properties of WC-Co materials
It can be seen clearly that both the thickness and the amplitude of the gradients within gradient WC-Co materials have a tendency to increase with increasing initial Co content and WC particle size, even though the experiments are conducted under different atmospheric conditions. This suggests that higher initial Co contents and larger WC particle sizes in WC-Co materials are beneficial for obtaining greater thickness and amplitude of cobalt gradient during carburizing process
Summary
Due to their unique microstructure and superior combinations of wear resistance vs. fracture toughness, functionally gradient WC-Co composites with cobalt (Co) content increasing from surface to the interior of the bulk of the material have been the objective of intensive research in the hardmetal industry for a long time [1,2,3]. The most successful one is the so called Dual Property carbide (DP carbide) process [4, 5], which is based on the carburization of fully sintered hardmetals with the low carbon contents and containing uniformly distributed Ș-phase (Co3W3C) at liquid phase sintering temperature. This technology allows the fabrication of gradient hardmetals with a very low Co content in the near surface layer, a significant disadvantage of these gradient hardmetals obtained by this approach is the presence of the very brittle core comprising much Ș-phase, which is detrimental to the mechanical properties of WC-Co materials. Such a functionally gradient WC-Co material having a Co depleted surface zone and not comprising the Ș-phase, has been found to be able to offer excellent mechanical properties and superior engineering performance, compared with conventional homogeneous WC-Co materials [8]
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