A comparative study of SiAlON ceramics

Abstract

Two different varieties of Si3N4 powders were used to prepare SiAlON ceramics. 100% beta-Si3N4 was used from refractory grade powders (B1) and another purer 98% alpha-Si3N4 (50A) powder was used to prepare the SiAlON samples. Since SiC + SiAlON composites reportedly perform better, batches were prepared with 15% SiC addition to the refractory powders (B1) and 17.5% SiC was added to the other SiAlON composition (50A). The samples were gas pressure sintered at 1840 degrees C and at 22 bar with 1 h dwelling time. Thereby, we could achieve 97-98% theoretical density. The hardness was recorded 14-17 GPa while fracture toughness varied from 4.3 to 5 MPa m(1/2). Fretting experiments showed initial running-in period of 300 cycles for all the tribo-couples. After which, the steady state coefficient of frictions (COF) were achieved. Steel ball of 10 mm diameter, fretting against 50A composition, showed 0.6 average steady state COF while the same composition while fretting against alumina ball of the same diameter, showed 0.57 average steady state COF. Results have been compared with SiAlON composition derived from refractory powder (B1) and found that the 50A composition performs better under identical test conditions. Moreover, cytocompatibility study also suggests that the investigated 50A composition can be used as substrate to support cell adhesion and proliferation of L929 mouse fibroblast cell lines whereas B1 composition derived from refractory powders are toxic in nature