Nippon Tungusten Review

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2001  Volume 33 

The Effect of Oxygen Introduction on Oxidation Resistance and Cutting Performance of Si3N4 Ceramics
Kokoro GOTO*1), Mituyoshi NAGANO*2), Hideaki SANO*1), Shigeya SAKAGUCHI*2)
*1) Department of Materials Science and Engineering, Faculty of Engineering, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
*2) Nippon Tungsten Co., Ltd. 3173-2 Oaza-sonobe, Kiyama-cho, Miyaki-gun, Saga 841-0203, Japan
Key words Si3N4 ceramics, oxidation, sintering, powder, Al2O3, solid solution, cutting tool


Si3N4 ceramics used in this study were introduced to oxygen during preparation by three different methods; (1) pre-oxidation of raw powder, (2) sintering in different atmospheres, (3) controlling the amount of Al2O3 to be added as a sintering additive. Their oxidation behavior in term of change in mass, morphology surface composition and cross-section of the specimen, was studied between temperature of 1200 and 1400°C Though mass change could hardly be seen below 1300°C, it was observed remarkably at 1400°C. In isothermal oxidation at 1400°C, as the amount of Al2O3 increases from 2mass% to 4mass%, the mass of the specimen also increases. However, the effect of pre-oxidation of raw powder and sintering in different atmospheres does not appear on oxidation resistant Si3N4 ceramics. Oxidized layers were formed on the surface of the specimen and they consist of two or three layers. Those specimens which had lower Al and O atom solid solution was superior to higher solution specimens, because lower solid solution specimens have greater hardness and strength. As a result, it was considered preferable that Al and O atom solid solution should be lower in the range of sinterability accerelation.
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