High Temperature Strength of β′-o′-SIALONS

Abstract

We prepared and evaluated β′-o′-Sialon having 15 vol% of o′-phase. The four-point bending strength at elevated temperatures of as-machined specimens were 690 MPa at 1200°, 610 MPa at 1350°, and 410 MPa at 1500°. The room temperature strength of oxidized specimens increased with the increase in annealing time up to 10 hrs, and decreased when the time exceeded 30 hrs. The strength at 1350° was substantially improved by oxidation annealing of 10 hrs at 1350°. These results suggested that two mechanisms be involved in the fracture of the oxidized sintered material, i. e., crack healing by an oxidized layer and residual stress caused by a thermal expansion mismatch between β′-o′-Sialon and the oxidized layer.