Effects of Metallic Boride Dispersion on Fracture Toughness and Oxidation Resistance in SiC Ceramics

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  • SiCにおける破壊靭性と耐酸化性に対する高融点金属ホウ化物粒子の分散効果
  • SiC ニ オケル ハカイ ジンセイ ト タイ サンカセイ ニ タイスル コウ

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Abstract

TiB2, ZrB2, HfB2, VB2, NbB2, TaB2, and WB were found to be dispersible particles to achieve the fully densified composites.<br>By dispersing the above metallic borides into SiC up to 20mol%, the fracture toughness of the composite increased linearly from 3.2MPa⋅m1/2 to about 5MPa⋅m1/2. The dispersed boride for the most effective toughening was not yet clariefied due to the large standard deviation of the experimental data and the large differences in particles size.<br>TiB2, ZrB2, HfB2, and TaB2, which formed oxides of TiO2, ZrSiO4, HfSiO4, and Ta2O5 through an oxidation reaction, induced severe corrosion. On the other hand, VB2, NbB2, MoB, and WB, which formed liquid phase of oxides such as V2O5, Nb2O5, and WO3, or gas phase such as MoO3 at 1500°C, showed a somewhat mild corrosion. The more preferable metallic borides seemed to be NbB2 and WB which formed lower equilibrium vapor pressure oxides only than VB2 and MoB.<br>In conclusion, NbB2 and WB seem to have bright prospects for developing new SiC composite ceramics that simultaneously realize sintering, toughening, and the least degrading in corrosive oxidation at 1500°C.

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