High Temperature Hardness of Si<sub>3</sub>N<sub>4</sub> Ceramics Fabricated under High Pressure

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  • 高圧力下において作製した窒化けい素焼結体の高温硬度
  • コウ アツリョクカ ニ オイテ サクセイシタ チッカ ケイソ ショウケツタイ

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Abstract

The temperature dependence of the Vickers microhardness (VMH) was measured for highly dense Si3N4 ceramics without and with oxide or nitride additives prepared by the high pressure hot-pressing or hot isostatic pressing. Rapid increase in room temperature VMH of the Si3N4 ceramics without additives with decreasing the amount of open pores was observed. The VMH (200g loads) of the fully dense Si3N4 ceramics without additives was 23GN/m2 at room temperature and 14GN/m2 at 1200°C, and this VMH at elevated temperature was higher than that of SiC single crystal. The VMH of Si3N4 ceramics obtained from α-Si3N4 was higher VMH not only at room temperature but also at elevated temperature than those obtained from β-Si3N4. The decrease in the VMH with increasing temperature for the Si3N4 ceramics with oxide additives was more rapid than that for the Si3N4 ceramics with nitride of the same element, and it was found that controlling the composition of the grain boundary phase was very important in the fabrication of Si3N4 ceramics. It is expected that rapid fall in the VMH of the Si3N4 ceramics with additives of elevated temperature was due to the ductile-brittle transition of these materials.

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