Thermal Stability of Low‐SiC Fiber (Hi‐Nicalon) Treated in a Hot Isostatic Press

The low‐oxygen SiC fiber fabricated by the electron‐beam irradiation curing method, Hi‐Nicalon, was heated at 1773 to 2273 K in a hot isostatic press (800 MPa of argon) and was subsequently reheated at 1873 K at 1 atm (101 kPa) of argon. The hot isostatic press treatment delayed the onset of fiber deterioration to higher temperature. The fiber strength remained almost unchanged by subsequent reheating at 1873 K in 101 kPa of argon. The thermal stability of Hi‐Nicalon, as a consequence of the permanent change in surface structure, can be greatly improved by treating in the hot isostatic press.