Understanding machinability improvements and removal mechanism of ceramic matrix composites during laser-ablating assisted grinding

Abstract

Ceramic matrix composites are advanced high-temperature materials for aerospace equipment, but they are also known as hard-to-machine materials. This study introduced laser-ablating assisted grinding (LAAG), and analyzed the complex physicochemical transformations of Cf/SiC composites during picosecond-laser ablating, then systematically explored the grinding characteristics, damage behavior, removal mechanism, and abrasive wear. It was revealed that Cf/SiC composites occurred sublimation and oxidation reactions during laser ablating, resulting in SiO2 ablation products with a loose microstructure. Grinding force, temperature and diamond wear remarkably decreased through LAAG. Besides, surface roughness was observably reduced, and the surface morphology of Cf/SiC composites was primarily shown as micro fracture and ductile removal. Furthermore, subsurface damages, including fiber pulling-out and interface debonding, were almost invisible after LAAG. More importantly, the graphite crystallites of carbon fibers near the ground surface became disordered, and an amorphous structure layer was first found on the micro-fractured carbon fibers. The grinding chips generated in LAAG were lamellar-fractured ablated materials rather than uncharacteristically-fractured fiber bundle, indicating the anisotropy removal behavior of Cf/SiC composites was decreased. The machinability improvements were especially significant when the laser scanning interval was small and the scanning direction was perpendicular to the grinding feed direction.