Influence of machining on the strength of SiC-Al2O3-Y2O3 ceramic

The influence of surface machining on the mechanical strength of SiC ceramics was investigated in terms of surface roughness, residual stress, and surface morphology observation. Experimental results showed that the mechanical strength of the SiC ceramic appears to correlate with the surface roughness of the ceramics: the lower the surface roughness, the higher the flexural strength. An average four-point bending strength of as high as 700 MPa, which is higher by a factor of 1.8 than the ceramic with as-fired surface, can be achieved after the surface of the specimens is polished with a 600-grit fine diamond wheel. More extensive surface polishing deteriorates the strength by forming large surface pores which act as failure origins. Machining-induced compressive residual stress in the thin surface layer of the ceramic appears to increase the fracture stress to only a limited extent.