研究論文
TiC-Ti-Mo2C硬質焼結材料の組織と機械的性質
キーワード:
TiC-Ti-Mo2C alloy,
powder metallurgy,
SEM microstructure,
Mo phase precipitation,
transverse-rupture strength
2020 年 67 巻 10 号 p. 571-580
詳細
2020 年 67 巻 10 号 p. 571-580
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.
