Amorphous silicoboron carbonitride ceramic with very high viscosity at temperatures above 1500°C

Recently, the viscosity of a predominantly amorphous silicon carbonitride (Si1.7C1.0±0.1N1.5) alloy with an apparent glass-transition temperature (Tg) of 1400°–1500°C was studied. In this study, the creep behavior of silicoboron carbonitride (Si2B1.0C3.4N2.3), which seems to have a Tg 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