EXPERIMENTAL CHARACTERIZATION OF HIGH-TEMPERATURE CREEP RESISTANCE OFMULLITE

The creep behaviour of mullite has been studied at temperatures betwee n 1100 degrees C and 1450 degrees C. The two standard stages, primary and steady state are observed. The steady state strain creep rate may be represented by the standard relationship: (epsilon) over dot = A si gma(n) exp(-Q/RT) with a stress exponent value n equal to about unity and an activation energy Q of about 410 kJ/mol at low temperatures and up to 731 kJ/mol for temperatures above 1300 degrees C. At high stres s or temperature specimens failed. SEM observations of the fracture su rface revealed that SCG played a major role in the failure process. Th e experimental lifetime values were compared to a simulation conducted by integration of V-K-I laws determined by Double Torsion technique a t 1200 and 1300 degrees C. A fair agreement is observed suggesting tha t the creep duration is limited by SCG which causes the material failu re, as assumed by Lange. (C) 1997 Elsevier Science Limited and Techna S.r.l.