Bend stress relaxation creep of CVD silicon carbide

Bend stress relaxation (BSR) creep of two forms of chemically vapor-deposited beta phase silicon carbide, namely polycrystalline and single-crystalline, was studied. The experiment was primarily oriented to demonstrate the applicability of BSR technique to irradiation-induced / enhanced creep behavior of silicon carbide in nuclear environments. It was demonstrated that thin strip samples with sufficient strength for BSR experiment could be machined and the small creep strains occurred in those samples could be measured to sufficient accuracy. The thermal creep experiment was conducted at 1573 - 1773K in argon to maximum hold time of 10 hours. Both materials exhibited similar primary creep deformation at the initial stresses of 65 - 100 MPa. The relative stress relaxation determined in the present experiment appeared significantly smaller than those reported for a commercial CVD SiC fiber at given temperature, implying a significant effect of the initial material conditions on the relaxation behavior. The analysis based on the relaxation time - temperature relationship gave an activation energy of ∼850 kJ/mol for the primary responsible process in CVD SiC.