Microstructural analysis of cemented tungsten carbide using orientation imaging microscopy (OIM)

Cemented tungsten carbide is one of the most widely produced powder metallurgy products. For the past 75 years cemented tungsten carbide tools have been performing at an increasingly popular rate. Fine-grain, especially nano-grain, cemented tungsten carbides make it possible to achieve a new range of properties that are improved from their present counterparts. Developments in powder processing enable us to produce true nano-size tungsten carbide powder (< 30 nm). Producing true nano-grain cemented carbide compacts remains a challenge. The conventional grain growth inhibitors are not able to inhibit grain growth of nano-grain carbides, and liquid phase sintering is not suitable for nano-grain carbides due to rapid grain growth. The only possible way to sinter of nano-grain size cemented tungsten carbide is solid state sintering. Several studies have focused on the sintering behavior of nanocrystalline WC-Co. The majority of densification and grain growth in the specimen occurs in solid state. Hence in order to achieve fully dense nano-grain size WC-Co, it is necessary to understand the underlying mechanism of densification and grain growth. In this study, a comprehensive microstructural analysis was carried out during solid state and liquid phase sintering on micron grade samples using Orientation Imaging Microscopy (OIM). Several microstructural parameters were analyzed to investigate the grain growth mechanisms. A comprehensive grain boundary analysis was also done to investigate grain boundary evolution during sintering, especially for the preferred misorientation. Since cemented carbide showed preferred prism shape in the micro structure, a faceting analysis was also carried out. OIM software does not provide tools for all of the analysis that were carried out in this study, so an algorithm for faceting analysis was generated and implemented.