Journal of the Japan Society of Powder and Powder Metallurgy
Online ISSN : 1880-9014
Print ISSN : 0532-8799
ISSN-L : 0532-8799
Paper
Microstructures and Mechanical Properties of TiC-Ti-Mo2C Sintered Hard Alloy
Kei TOKUMOTOKenji NAKAHARAKatsuya MASHIMAShinzoh MITOMI
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JOURNAL OPEN ACCESS

2020 Volume 67 Issue 10 Pages 571-580

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Abstract

TiC-47 mass% Ti-20 mass% Mo (Mo added alloy) and TiC-52 mass% Ti-21 mass% Mo2C (Mo2C added alloy) were prepared through powder metallurgy. The TiC grain size of Mo2C added alloy sintered at 1673 K was about 3 μm, which was smaller than that of the Mo added alloy. The mechanism was considered as follows. First, when C diffuses from Mo2C to α-Ti, the Mo phase containing defects such as vacancies precipitates. Second, the solid solution of Mo and Ti is promoted by the mutual diffusion between the precipitated Mo phase and α-Ti, and the transformation from α-Ti to β-Ti occurs. Third, the solute diffusion coefficient of β-Ti is much larger than that of α-Ti, so C diffuses from TiC to β-Ti, producing TiC0.6. Meanwhile, Mo has a smaller free energy for carbide formation than Ti has and then TiC0.6 cannot contain Mo, so Mo is concentrated in β-Ti adjacent to precipitated TiC0.6. This suppresses the growth of TiC0.6, and then the grain size of TiC0.6 becomes smaller. The transverse-rupture strength of the Mo2C added alloy was 20% higher than that of the Mo added alloy, reaching 0.95 GPa. At that time, both alloys have almost the same hardness.

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