Abstract
Si3N4 powders mixed with 6wt%Y2O3-2-6wt%Al2O3 and 6wt%Y2O3-1.5wt%MgO as sintering aids, were pressed and normally sintered at 1600°C. The sintered compacts were HIP'ed without capsule using in 100 MPa nitrogen gas at 1700°C. Density, weight change, a to β phase transformation and flexural strength were studied, and the results obtained were summarized as follows:(1) The amount of weight loss during sintering was relatively small in case of Y2O3-Al2O3 series, so that the sinterability was better than in Y2O3-MgO series.(2) In case of both the series, the amount of a to β transformation in sintered compacts was decreased compared with the compacts which contained 6 wt%Y2O3 only, and the tendency in Y2O3-Al2O3 series was more remarkable than in Y2O3-M90 series.(3) The mean strength of Y2O3-Al2O3 series was improved from 340 to 700 MPa by HIP treatment. It was found that the improvement of strength depended on not only density, but also a toβ transformation and fibrous structure formation in Si3N4 during HIP treatment.
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