Probing formation and evolution of SiC/SiC composites surface/subsurface damages induced by diamond-grain scratching

• SiC/SiC composites model is established with fiber position and diameter randomly distributed. • Fiber orientation greatly affects the surface/subsurface damage formation. • Grinding along longitudinal fibers results in little subsurface damage. • Severe subsurface fiber radial fracture occurs on normal fibers. • Grinding depth affects surface/subsurface damage variably due to grinding direction. SiC/SiC composites are promising materials for turbine blades, but severe damages easily occur during grinding, significantly decreasing the fatigue life and service reliability of components. This study developed a representative volume element model of SiC/SiC composites with fiber position and diameter randomly distributed, combined with single diamond grain scratching experiments to reveal the removal mechanism and surface/subsurface damage characteristics. Simulation results showed that when scratching along perpendicular fibers, the scratched surface was relatively smooth, but severe subsurface radial cracks occurred in the SiC fibers; interestingly, these cracks could hardly extend into the SiC matrix, even when the scratching depth increased. Fiber fracture and pull-out damages also appeared far from the scratching area when scratching along transverse fibers. Besides, some macrocracks appeared on the subsurface of the SiC matrix, but they deflected once reaching SiC fibers. In contrast, when scratching along longitudinal fibers, damages occurred only within the scratching depth, and minor damage appeared on the subsurface; the phenomenon remained unchanged when the scratching depth increased. The surface and subsurface damages obtained from the simulation were in high agreement with those from experiments.