Amorphous Silicoboron Carbonitride Ceramic with Very High Viscosity at Temperatures above 1500°C

Abstract

Recently, the viscosity of a predominantly amorphous silicon carbonitride (Si 1.7 C 1.0±0.1 N 1.5 ) alloy with an apparent glass‐transition temperature ( T g ) of 1400°–1500°C was studied. In this study, the creep behavior of silicoboron carbonitride (Si 2 B 1.0 C 3.4 N 2.3 ), which seems to have a T g value of >1700°C, was examined. Both materials exhibited a three‐stage creep behavior. In stage I, the creep rate declined, because of densification. In stage II, the strain rate approaches a steady state. In stage III, it resumes a declining strain rate, which ultimately decreased below the measurement limit of the system. At 1550°C in stage II, the viscosity of silicoboron carbonitride was six orders of magnitude higher than that of fused silica. Among the Si‐C‐N ceramics, only chemical‐vapor‐deposited and reaction‐bonded silicon carbides seem to have greater creep resistance than the silicoboron carbonitrides at temperatures >1550°C.