Fracture Behavior of Chemically‐Vapor‐Deposited SiC‐Coated Graphite: I, Experimental Results

CVD SiC coatings on polycrystalline graphite substrates exhibited a crack arrest/multiple cracking phenomenon when fractured in four‐point flexure. This fracture behavior appeared to be controlled by the magnitude of the coating thickness. When the coating thickness exceeded ∼50 μm, catastrophic failure of the sample was observed. However, when the coating thickness was less than ∼50 μm, crack arrest and multiple cracking were observed in the tensile coating surface before catastrophic failure of the composite. In order to understand the fracture behavior of the layered composites, it was necessary to characterize coating thickness and strength as well as the fracture toughness of the substrate and the state of residual stress in the system.