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An advanced self-toughening silicon nitride ceramic tool YL16A has been developed by adding proper additive Y 2 O 3 -La 2 O 3 into the phase silicon nitride and using the hot press fabrication technology. It is found from a scanning electron microscope (SEM) observation that the self-toughening mechanisms of the new ceramic tool material are columnar grain bridge and pullout similar as the whisker reinforcing mechanisms. Some -Si 3 N 4 grains are converted into columnar -Si 3 N 4 grains with a high aspect ratio, and improve the fracture toughness of the new silicon nitride ceramic tool. The tests of mechanical properties, and wear and fracture resistance in machining are finally conducted. It is shown that the wear resistance of YL16A is almost the same as that of a commercially available alumina matrix ceramic tool SG4 and the fracture resistance of YL16A is markedly stronger than that of SG4. The new self-toughening ceramic tool YL16A can increase the tool-life by fracture by about 388% as compared to SG4 when intermittent cutting a quenched mild carbon steel. While the fracture toughness of the new ceramic tool is improved by up to 112-130% compared with other two general ceramic tool materials.

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