TiC-TiN-Mo2C-Cr3C2系複合セラミックスにおけるMo2Cの焼結性改善効果

概要

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Addition of Mo2C and TiN to TiC-Cr3C2 ceramic composite was tryed to develop for cutting tool materials. The compacts of the powder mixture consisting of 70%TiC-15%TiN-7%Mo2C-8%Cr3C2 were sintered at temperatures up to 1600°C for 2 hr in a vaccum of 10-1 mmHg having feeble carburizing attribute. The compacts showed distinguished sintering ability similar to liquid phase sintering of alloys. That is to say, the compacts attained complete densification by sintering at 1350°C. Mo2C was dissolved in TiC readily at temperatures below 1200°C, which resulted in the formation of (Ti Mo) C solid solution. It was presumed that Mo2C was dissolved in the form of ζ-MoC having NaCI type cubic lattice. It is likely that carbon content in the solid solution was substantially reduced due to the dissolution as MoC, because no metallic molybdenum was detected in the specimens in which Mo2C was dissolved in TiC. It means the increment of carbon vacancy in the solid solution. This promotes dissolution of TiN into (Ti⋅Mo)C solid solution, which will play an important role as the main driving force of densification. At 1350-1400°C, metallic impurities of iron group in the ceramic composite of about 0.8%, as well as that in TiC-Cr3C2 system, were fully dissolved into low-chromium carbides.
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