ENHANCED MACHINABILITY OF SILICON-CARBIDE VIA MICROSTRUCTURAL DESIGN

The machinability of a heterogeneous silicon carbide with weak interph ase boundaries, elongated grains, and high internal stresses is evalua ted relative to a homogeneous control material with a well-bonded, equ iaxed, 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 dislodgemen t in place of the more conventional macrofracture chipping mode of rem oval. 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.