Compressive creep of mullite containing Y2O3

Compressive creep of mullite and mullite containing 5 and 9 wt% Y{sub 2}O{sub 3} has been investigated in the temperature range of 1300-1400 C over stresses between {approx}0.6 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{+-}20 kJ/mol. It is likely that the rate-controlling diffusing species is oxygen. Creep of the Y{sub 2}O{sub 3}-containing specimens was similar to that of the pure mullite at 1300 C. Near and above the temperature at which melting was observed in DTA, the Y{sub 2}O{sub 3}-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 Y{sub 2}Si{sub 2}O{sub 7}, but the crystallized specimens exhibited cavitation at larger strains.