Impact damage of narrow silicon carbide (SiC) ceramics with and without environmental barrier coatings (EBCs) by various foreign object debris (FOD) simulants

The leading and trailing edges of turbine airfoils are highly susceptible to impact by foreign object debris (FOD) entrained in the gas stream of turbine engines. In this study, a narrow specimen geometry is implemented to study the FOD impact behavior of low curvature airfoil edges. Silicon carbide (SiC) ceramic specimens with and without an environmental barrier coating (EBC) are used as target materials. The EBC consists of an air plasma sprayed mullite topcoat (similar to 166 mu m) and silicon bond coat (similar to 58 mu m). Spherical (empty set 1.5 mm) FOD simulants of silicon nitride (Si3N4), partially stabilized zirconia (PSZ), and steel are used as impactors. A modified gas gun is used to generate impact damage at normal incidence and velocities ranging between 300 to 400 m/s. In situ phase contrast X-ray radiographs, which render 2D representations of the internal transient damage, are captured during the impact experiments. Impactor hardness and toughness are found to primarily influence damage in the coating. Relative to wide specimens, the narrow specimens experience a greater level of cracking and this is postulated to result from reduced self-confinement. Irrespective of specimen geometry and impactor material type, limited cracking (i.e. enhanced shielding) is observed for the coated condition.

Automated summary

The study found that damage caused by FOD on the leading and trailing edges of turbine airfoils is influenced by the material coating, with hardness and toughness being the primary factors. Narrow specimens are more prone to cracking damage compared to wide specimens, possibly due to reduced self-confinement. Limited cracking is observed under coated conditions, regardless of specimen geometry and impactor material type.