FORMATION OF AN ALPHA-SIAION LAYER ON BETA-SIAION AND ITS EFFECT ON MECHANICAL-PROPERTIES

We have developed a technique for in situ formation of an alpha-SiAlON layer on sintered beta-SiAlON. The technique consists of packing a po wder compact of beta-SiAlON composition with alpha-SiAlON composition powder, presintering, and sintering. Using this technique, it is possi ble to control the thickness of the layer by changing the presintering conditions during heating to a sintering temperature. The introductio n of an alpha-SiAlON layer increases the surface hardness and improves the wear and oxidation resistance, with a moderate reduction of flexu ral strength. The surface modification of beta-SiAlON may provide oppo rtunities of wider application of beta-SiAlON to wear- and oxidation-r esistant components.