Foreign object damage (FOD) behavior of two commercial gas-turbine-grade silicon nitrides, AS800 and SN282, was determined at ambient temperature through postimpact strength testing of target disks impacted by steel ball projectiles with a diameter of 1.59 mm in a velocity range from 115 to 440 m/s. AS800 silicon nitride exhibited a greater FOD resistance than SN282, primarily due to its greater value of fracture toughness (K-lc). The critical impact velocity V-c for which the corresponding postimpact strength was the lowest was V(c)approximate to440 and 300 m/s for AS800 and SN282, respectively. A unique lower strength regime was typified for both silicon nitrides depending on impact velocity and was attributed to significant radial cracking. The damage generated by projectile impact was typically in the form of ring, radial, and cone cracks with their severity and combination being dependent on impact velocity. Unlike the thick (3 mm) flexure bar target specimens used in previous studies, the thin (2 mm) disk target specimens exhibited a unique back-side radial cracking on the reverse side just beneath the impact sites at and above impact velocities of 160 m/s for SN282 and 220 m/s for AS800. (C) 2004 Kluwer Academic Publishers.