Characterization of Subsurface Damage of Deterministic Microgrinding Silicon Carbide
Thomas Ryan Smith, MS Defense
Monday, July 30, 2018
Manufacturing the different grades of Silicon Carbide proves extremely difficult due to its hardness and fracture toughness. We aim to study the subsurface damage initiated by deterministic microgrinding and diamond turning for various grades of Silicon Carbide, namely Chemical Vapor Deposited and Reaction Bonded. Silicon Carbide is of interest for optical components because of its high thermal stability and specific stiffness.
The Chemical Vapor Deposited Silicon Carbide was ground in two operations using OptiPro’s computer numerically controlled grinding machine, the SX50. Reaction Bonded Silicon Carbide was diamond turned using three increasingly finer grit sizes at University of North Carolina at Charlotte.
The subsurface damage of Chemical Vapor Deposited Silicon Carbide was revealed by sub-aperture polishing spots onto the surface using UltraForm and Magnetorheological Finishing. The material removal rates of UltraForm Finishing and the surface roughness evolution from spot polishing were determined using optical methods. The residual stress on the surface initiated by grinding was characterized using Vicker’s micro-indentation.
Reaction Bonded Silicon Carbide was also spot polished with UltraForm Finishing to characterize how polishing tool stiffness affected material removal in two-phase substrates.
The subsurface damage for ground Chemical Vapor Deposited Silicon Carbide penetrated about 2 µm into the surface. Magnetorheological Finishing proved to more quickly relieve compressive residual stresses from grinding but UltraForm Finishing was faster at reducing surface roughness. UltraForm Finishing also successfully polished two-phase Reaction Bonded Silicon Carbide without preferentially polishing Silicon; however, the issue of belt signature must be addressed to make this a viable finishing method.