The Microstructural and Mechanical properties of platelet (W,M1,M2)C-Co Ternary System

Abstract

WC-Co cemented carbides are widely used as the material in making cutting tools due to their superior wear resistance, hardness, and toughness. The WC particles that are embedded on the cobalt binder are grown by Ostwald ripening during liquid phase sintering. It has been found that the morphology of WC particles in the cobalt binder consists of platelets, a feature which enhances the materials toughness by deterring crack propagation. By controlling the high energy ball milling, the temperature during reduction, the addition of TiC, the nano effects, and so forth, one can observe the formation of platelet WC. Until now, the most successful way of controlling the growth of WC grain is with the addition of small amounts of WC grain growth inhibitors. Our previous research on the microstructure evolution of the WC platelet, tungsten carbide particles demonstrated that the morphology, size, and mechanical properties of WC-Co cermets change significantly with the addition of transitional metals such as titanium carbide (TiC), vanadium carbide (VC), and chromium carbide (Cr2C3). Especially in case of TiC, (W,Ti) C-phase was found to have formed with a thin, platelet morphology, enhancing the toughness of the (W,Ti) C-Co cermets. The purpose of this research was to enhance the hardness of the material by controlling the size and morphology of WC platelets and by maintaining the same toughness for different systems with the addition of NbC to the initial, binary WC-Co system. In this research, four different ternary systems (such as in-situ, hybrid one and two, and conventional) were prepared using TiC and NbC to control the size and morphology of tungsten carbide platelets. The mole fraction of TiC was fixed at 0.1 in all of the systems, and the NbC mole fraction varied between 0.07 and 0.1 in all of the systems as well. The alloys that started with the oxide powder were produced via planetary milling, and those that started with carbide powder were prepared through ball milling, then all of the systems were sintered at 1450˚C for 1 hour. Analysis of the microstructure revealed that all of the systems contained WC platelets and that their aspect ratios had increased when TiC and NbC were added simultaneously. Thus, the addition of transitional metals was found to be effective in increasing the aspect ratios of the different systems that were studied in this research