Abstract
An experimental investigation was conducted for evaluating the effect of oxidation in air and flexural strength of the hot pressed silicon nitride, containing Y2O3 and Al2O3 additives. The effects of oxidizing variables, temperature and time were investigated. The specimens were high efficiently ground before oxidation, and examined the relation between the oxide conditions and flexural strength. The grinding machine was a machining center with a high rigid spindle. The surfaces of the oxidized specimens were covered with a uniform oxide layer. It was found that the oxide layer consisted of SiO2 and Y2O3·2SiO2, from the X-ray diffraction analysis. After the oxidation, the compressive residual stress in the ground surface was decreased. The flexural strength of the oxidized specimens was significantly increased at room temperature. For recover the strength of the high efficiently ground specimens, there were suitable oxidizing conditions. After the oxidation at 1200°C for 24 h, the flexural strength was most increased in this investigation.
