Improved Impact Fracture Resistance in Oxidation-Toughened Si3N4-20 Vol% ZrO2

摘要

Dr. F. F. Lange is using an oxidation technique to induce compressive stresses in the near-surface regions of Si3N4-ZrO2 specimens. Silicon nitride powder is first thoroughly mixed with about 20 vol% zirconium oxide and 4 vol% Al2O3 powders, then hot pressed to achieve a fully dense plate. The plate is then given a subsequent anneal at 700 C for 5 hr in air. The zirconium oxynitride within several grain diameters of the surfaces is oxidized to the monoclinic form with an accompanying increase in molar volume of about 4-5%. The expansion of the lattice in the surface regions gives rise to substantial compressive stresses on the surface (and significant tensile stresses in the interior).