Failure of brittle materials starts in general from defects which exist in the volume or on the surface of the specimens. Surface flaws, which are more dangerous than volume flaws, can be introduced by machining. They decrease the strength of specimens and components. This investigation compares two different ways to avoid surface defects and, as a consequence, increase the strength.
For the investigation disc shaped silicon carbide samples were machined with different machining conditions. As expected, it could be shown that a better (gentler) machining increases the strength. In order to heal the surface defects a sample of specimens was heat treated and then tested with the B3B-test. Microstructural investigations (SEM, FIB) reveal the formation of a thin glassy layer which heals the cracks on the surface if these are not too large.
It was observed that a better machining as well as annealing (depending on machining conditions and healing temperature, respectively) leads to a significant increase of strength (up to 250%) in the same amount.