Enhanced Machinability of Silicon Carbide via Microstructural Design
Nitin P. Padture, Christopher J. Evans, Hockin D. Xu, Brian R. Lawn
The machinability of a heterogeneous silicon carbide with weak interphase boundaries, elongated grains, and high internal stresses is evaluated relative to a homogeneous control material with a well-bonded, equiaxed, and unstressed grain structure. Drilling and grinding rates for the silicon carbide are substantially enhanced by the microstructural heterogeneity--the weak boundaries enable easy grain-scale dislodgement in place of the more conventional macrofracture chipping mode of removal. At the same time, the residual machining damage in the machined surfaces is significantly less strength degrading in the heterogeneous material. Implications concerning the microstructural design of flaw-tolerant ceramics for enhanced machinability are considered.