Impact resistance of environmental barrier coated SiC/SiC composites

Impact performance of 2D woven SiC/SiC composites coated with 225 and 525 mu m thick environmental barrier coating (EBC) was investigated. The composites were fabricated by melt infiltration and the EBC was deposited by plasma spray. Impact tests were conducted at room temperature and at 1316 degrees C in air using 1.59 mm diameter steel-balls at projectile velocities ranging from 110 to 375 m/s. Both microscopy and non-destructive evaluation (NDE) methods were used to determine the extent of damage in the substrate and coating with increasing projectile velocity. The impacted specimens were tensile tested at room temperature to determine their residual mechanical properties. At projectile velocities less than 125 m/s, no detectable internal damage was noticed in the MI SiC/SiC composites coated with 525 mu m EBC. With increase in projectile velocity beyond this value. spallation of EBC layers, delamination of fiber plies, and fiber fracture were detected. At a fixed projectile velocity, the composites coated with 525 mu m EBC showed less damage than those coated with 225 mu m EBC. Both types of coated composites retained a large fraction of the baseline proper-ties of the as-fabricated composites and exhibited non-brittle failure after impact testing. Furnace exposure of impacted specimens in a moisture environment at 1316 degrees C for 500 h indicated that the through-the-thickness cracks in the coating and delamination cracks in the substrate generated after impact testing acted as conduits for internal oxidation. (C) 2007 Elsevier B.V. All rights reserved.