In situ tensile behavior of Hi‐Nicalon silicon carbide fibers exposed to high‐temperature argon plasma

Abstract

Direct mechanical characterization of silicon carbide fibers in extreme hypersonic aerothermal environment is critical to the development of next-generation inflatable thermal protection systems that could enable delivery of large payloads to planetary surfaces. In this article, we report direct measurements of tensile properties in Hi-Nicalon silicon carbide fibers exposed to high-temperature argon plasma exceeding 1100°C using an in situ mechanical testing system integrated into a 30-kW inductively coupled plasma torch chamber simulating the hypersonic atmospheric entry conditions. As a comparison, ex situ tensile tests were performed on virgin Hi-Nicalon silicon carbide fibers in both ambient air and vacuum conditions. In situ thermal and optical imaging was used to obtain a real-time resolution of the thermo-mechanical events occurring on the fibers during the high-temperature argon plasma exposure. It is found that the hightemperature tensile strength of Hi-Nicalon fiber tows exposed to argon plasma is 0.74 ± 0.19 GPa, which denotes a 59% reduction from the virgin fiber strength in ambient air (1.81 ± 0.19 GPa). Fractographic characterization by scanning electron microscopy shows that the substantial degradation of tensile strength in Hi-Nicalon fibers results from a reduction of fiber cross-section due to active surface attack from high-temperature argon plasma.