Compressive creep of mullite containing Y2O3

Compressive creep of mullite and mullite containing 5 and 9 wt% Y2O3 has been investigated in the temperature range of 1300-1400 degreesC over stresses between approximate to0.6 and 40 MPa in air. The nominally single-phase mullite deforms by diffusional flow with a stress exponent of 1 (for higher stresses) and an activation energy of 385 200/mol. It is likely that the rate-controlling diffusing species is oxygen. Creep of the Y2O3-containingspecimens was similar to that of the pure mullite at 1300 degreesC. Near and above the temperature at which melting was observed in DTA, the Y2O3-containing specimens crept significantly faster than the pure mullite. Models of creep of materials that contain a glass phase can explain most, but not all, of the observed behavior. Creep rates were not significantly affected by partial crystallization of the glass to Y2Si2O7, but the crystallized specimens exhibited cavitation at larger strains. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.