Strengthening of Machinable Glass-Mica Composites

Abstract

The effect of additives has been studied to improve the strength of machinable glass-mica ceramics. Titania, Y2O3-doped partially stabilized zirconia (Y-PSZ) and celsian (Ba1-xSrxAl2Si2O8, x=0, 0.1 and 0.2) powders (10 mass%) were mixed to the previously prepared glass-mica powder (content of F-flogopite: 45 vol%) by using a ball mill. The ball-mill grinding without additives improves the strength from 144 to 172 MPa through the size reduction of mica grains and the increase in sintered density. The addition of TiO2 and Y-PSZ is more effective to the microstructural refinement and the strengthening (190 MPa/TiO2, 220 MPa/Y-PSZ). Y-PSZ particles are segregated to the longitudinal ends of mica grains and suppress their longitudinal growth. It is expected that the Y-PSZ particles act as the reinforcements to the glass matrix to enhance the strength. The growth of titania particles under sintering results in the limited effect to structural refinement and the smaller strength than that for Y-PSZ-doped materials. The addition of celsians is further effective to the size reduction of mica grains and related densification to improve the strength (203-241 MPa) markedly. The celsian particles do not show their coarsening as well as Y-PSZ, and dissolve to the glass phase during sintering gradually. It is considered that the dissolution of celsians suppresses the growth of mica grains by changing the chemical composition of the glass phase. The increase of Young's modulus of the celsian-doped glass phase should also contribute to the strengthening.