Creep behavior of a zirconium diboride-silicon carbide composite

Flexural creep studies of ZrB2-20 vol% SiC ultra-high temperature ceramic were conducted over the range of 1400-1820 degrees C in an argon shielded testing apparatus. A two decade increase in creep rate, between 1500 and 1600 C, suggests a clear transition between two distinct creep mechanisms. Low temperature deformation (1400-1500 degrees C) is dominated by ZrB2 grain or ZrB2-SiC interphase boundary and ZrB2 lattice diffusion having an activation energy of 364 +/- 93 kJ/mol and a stress exponent of unity. At high temperatures (>1600 degrees C) the rate-controlling processes include ZrB2-ZrB2 and/or ZrB2-SiC boundary sliding with an activation energy of 639 +/- 1 kJ/mol and stress exponents of 1.7 < n < 2.2. In addition, cavitation is found in all specimens above 1600 degrees C where strain-rate contributions agree with a stress exponent of n = 2.2. Microstructure observations show cavitation may partially accommodate grain boundary sliding, but of most significance, we find evidence of approximately 5% contribution to the accumulated creep strain. (C) 2013 Elsevier Ltd. All rights reserved.