C-ring testing of nuclear grade silicon carbide composites at temperatures up to 1900 °C

Abstract

Silicon carbide matrix reinforced with silicon carbide fiber (SiC-SiC) composite is an advantageous material for many high temperature applications due to retention of room temperature strength above 1100 °C, which is the current operational limit for many high temperature metals. For the nuclear industry, this property, along with excellent radiation tolerance, has made SiC-SiC an attractive cladding material for the accident tolerant fuel program. The mechanical strength at high temperatures of these composites needs to be evaluated to address improvements in the third generation of Nicalon fibers, fabrication processes, as well as tested in a form-factor relevant to fuel cladding. In this work, mechanical strength of SiGA™ composite tubes, a SiC-SiC composite fabricated at General Atomics using the current generation of Hi-Nicalon Type S SiC fiber and chemical vapor infiltration processing (CVI) of the matrix, was evaluated at temperatures up to 1100 °C in ambient air and ∼1900 °C in an inert gas environment with nominal 30–60 min dwell time. The results of this study show full retention of room temperature strength at both test regimes. Some degradation of material toughness was observed at temperatures above ∼1760 °C. During this study, effects of interphase, fiber, and matrix morphological changes as a function of temperature were investigated.