Effect Of Molybdenum Addition On The Microstructure And Mechanical Properties Of Cemented Carbides

Cemented carbides, consisting of refractory metal compounds and the binder metals, are hard composites obtained by powder metallurgy process, usually concluding powder manufacture, pressure formation and high-temperature sintering. It has been considered as a kind of indispensable material in relative industry field due to many of its good properties. In this paper, different content of Mo were added into cemented carbide YT15 to fabricate specimens with powder metallurgy techniques. The microstructure of specimens was investigated using the X-ray diffraction (XRD) and scanning electron microscope (SEM). Chemical compositions of different phases were analyzed quantitatively by EDX. The analysis results of the examinations mentioned above were used to explain distinguishes between the mechanical properties of different Mo content specimens.This thesis is composed of five chapters. In the first chapter, the development history and researching actuality of WC-Co cemented carbides as well as its orientations of research and development were briefly introduced. Based on above work, the purposes and significance of this thesis have also been pointed out. Meanwhile, researches on the improvements of sintering process and the optimizations of compositions of cemented carbides were also illustrated.In chapter two, raw powders and manufacture techniques of WC-Co cemented carbides were introduced briefly. In chapter three, we focused on the testing method of mechanical properties and characterization method of microstructure of WC-Co cemented carbides.In chapter four, the relationships between the composition, microstructure and properties of cemented carbides with different Mo content were discussed, and we reviewed the effect of different Mo addition on the microstructure and mechanical properties of cemented carbides. Results show that: 1) The microstructure became fine with the increase of addition of Mo powder. 2) When the Mo content of cemented carbides was not more than 5wt. %, the transverse rupture strength and the hardness of specimens were enhanced since the microstructure became finer and finer with the increase of Mo addition. 3) If the addition of Mo contents is more than 5wt. %, there will form a new phase,η1 phase which was examined by primary researches to be the inter-metallic compound (Co₃Mo_1.5W_1.9)C_x. And the relative mechanical properties of cemented carbides will decrease because of the high brittleness of the new phase. 4) It is found that the fracture toughness presented a trend of continuously decline when the Mo addition of cemented carbides increased from 0wt. % to 10wt. %.Chapter five summarized the whole thesis and gave some advices on future works.