Journal of Materials Science, Vol.34, No.18, 4393-4398, 1999
High-temperature creep response of a commercial grade siliconized silicon carbide
Creep studies conducted in four-point flexure of a commercial siliconized silicon carbide (Si-SiC, designated as Norton NT230) have been carried out at temperatures of 1300, 1370, and 1410 degrees C in air under selected stress levels. The Si-SiC material investigated contained similar to 90% alpha-SiC, 8% discontinuous free Si, and 2% porosity. In general, the Si-SiC material exhibited very low creep rates (2 to 10 x 10(-10) s(-1)) at temperatures less than or equal to 1370 degrees C under applied stress levels of up to 300 MPa. At 1410 degrees C, the melting point of Si, the Si-SiC material still showed relative low creep rates (similar to 0.8 to 3 x 10(-9) s(-1)) at stresses below a threshold value of similar to 190 MPa. At stresses > 190 MPa the Si-SiC material exhibited high creep rates plus a high stress exponent (n = 17) as a result of slow crack growth assisted process that initiated within Si-rich regions. The Si-SiC material, tested at temperature less than or equal to 1370 degrees C and below the threshold of 190 MPa at 1410 degrees C, exhibited a stress exponent of one, suggestive of diffusional creep processes. Scanning electron microscopy observations showed very limited creep cavitation at free Si pockets, suggesting the discontinuous Si phase played no or little role in controlling the creep response of the Si-SiC material when it was tested in the creep-controlled regime.