SiO2 나노 콜로이달 첨가량에 따른 질화규소의 균열치유거동

Abstract

This study analyzed the characterization of bending strength of Si3N4 composite ceramics based on variations in the amount of nano colloidal SiO2 added. Semi-elliptical cracks about 100㎛ in length were obtained from a Vickers indenter using a load of 24.5 N. The results showed that the use of an optimum amount of added colloidal SiO2 and the coating of colloidal SiO2 on the cracks could significantly increase the bending strength. The crack-healed specimens showed the highest crack-healing strength at the crack-healing temperature of 1,273 K regardless of whether SiO2 nano colloidal was used. With regard to the bending strengths of Si3N4 composite ceramics according to additive SiO2 nano colloidal, it can be concluded that 1.3 wt.% of the colloidal SiO2, which gives the highest bending strength for smooth and crack-healed specimens, represents the optimum amount. The bending strength of a smooth specimen without the colloidal SiO2 coating exhibited the highest crack-healing strength at the SSTS-2 specimens. However, the bending strength of heat- treated smooth specimen with the colloidal SiO2 coating exhibited the highest crack-healing strength at the SSTS-1 specimens. Limiting temperature for bending strength of a crack-healed zone for bending strength was about 1273 K. However, the bending strength of SSTS-3 and SSTS-5 increased considerably while that of SSTS-1 and SSTS-2 decreased at a temperature of 1,573 K. In addition, the crack-healing characteristics of specimens according to the crack lengths and the coating methods of Si3N4 composite ceramics with long cracks were analyzed. Cracks of about 100 ~ 500㎛ in length were obtained from a Vickers indenter using the load of 24.5 ~ 98 N. In the case of a crack using a load of 24.5 N, the crack-healed specimen with SiO2 nano colloidal coating exhibited the highest bending strength, which increased by about 140% compared to that of a smooth specimen, but the multi crack-healed specimens with SiO2 nano colloidal coating had a lower bending strength than that of a smooth specimen. However, the bending strength of most multi-crack specimens slightly increased compared to that of the cracked specimens. Based on these results, the crack healing characteristic of multi indentation Si3N4 ceramics according to the coating methods was studied. In this study, the most effective coating method on the long-crack specimens was hydrostatic pressure coating.