Some aspects of solid solution grain growth inhibitors in cemented tungsten carbides

Abstract

Cemented tungsten carbides are the materials of choice for applications requiring superior wear resistance with high strength and toughness. Recently, there has been a growing interest in using ultrafine-grained cemented carbides to exploit the benefits of superior properties and improved performance. Finer grain carbides, due to higher interface area, are more susceptible to grain growth, and processing of these carbides requires uniform distribution of the inhibitor phase(s) to promote a homogeneous microstructure.A new class of grain growth inhibitor alloys has been developed, which enables better control of WC particle coarsening during liquid phase sintering of WC-Co-based powder compacts. The new alloys are formulated as solid solutions of the selected inhibitor carbide phases (VC and/or Cr3C2) in the Co metal binder phase. The solid solution approach realizes a much more uniform dispersion of the inhibitor carbides in the green body, thereby ensuring more effective mitigation of WC grain growth during liquid phase sintering. A significant reduction in the melting point of the Co-rich matrix by the addition of the inhibitor phases contributes to the reduced WC coarsening rate. Another contributing factor, and possibly the most important mechanism, is the decrease of solubility and transport of W and C atoms from one grain to the adjacent one, thus, further restricting the WC coarsening rate. Examples of using the solid solution grain growth inhibitors and some of the related mechanisms of grain growth inhibition will be described in this paper.