Coupled Effect of Angle of Incidence and Temperature on the High-speed Particle Impact Cratering and Erosion of Graphite

Materials in many high-speed applications are impacted by particles at varying obliquities and elevated temperatures. Previous studies have predominantly focused on understanding the formation of craters due to normal (90°) impact. However, the mechanisms and the extent of material erosion are known to be highly dependent on both the angle of incidence of the impinging particle and the surface temperature of the target material. To study the concurrent influence of these parameters, the laser-induced particle impact testing (LIPIT) method with high-temperature and oblique impact experiment capabilities is employed. Alumina (Al2O3) microspheres with nominal diameters of 60 μm are accelerated to velocities between 422 and 508 m/s and impacted on ultrafine-grain graphite (POCO ZXF-5Q) at varying angles of incidence (as low as 7°) at room temperature and while heated to 1000°C in air. The cratering morphologies and erosion mechanisms, along with their dependence on the impact angle and temperature, are studied in situ via high-speed imaging and postmortem using scanning electron microscopy (SEM) and laser scanning confocal microscopy. The maximum eroded volume per deposited kinetic energy is found to occur at angles between 35° and 45°. The graphite material heated to 1000°C is observed to experience oxidation pitting and up to 1.6 times higher impact erosion than the room temperature counterpart. A functional relation is fit to the data for the impact angle dependence of kinetic energy-normalized eroded volume.