Internal friction behavior of C/SiC composites with environmental barrier coatings in corrosive environment

Internal friction (IF, Q^-1) behavior of C/SiC composites that were coated with two kinds of environment barrier coatings, scandium disilicate (Sc₂Si₂O₇) and barium aluminosilicates (BaAl₂Si₂O₈, BAS), were investigated in corrosive environments. The Sc₂Si₂O₇-coated C/SiC composites were subjected to 50%H₂O-50%O₂ water vapor at 1400°C and BAS-coated C/SiC composites were exposed to molten Na₂SO₄ coupled with 50%H₂O-50%O₂ water vapor at 900°C. The values of Q^-1 for the samples corroded at different times were recorded by means of a forced nonresonant technique. The weight loss and flexural strength as a function of corrosion time were measured. The microstructural evolution of the corroded specimens at different periods was also studied. The results indicate that the value of Q^-1 of the coated C/SiC composites varies with their corrosion behaviors. The main factors that determine the IF behavior of the composites subjected to corrosion environments are the oxidation and corrosion of their fibers and interface.