Creep mechanisms and microstructure evolution of Nextel™ 610 fiber in air and steam

Creep rates of Nextel™ 610 alumina fibers were measured at 1100 °C and 100–500 MPa in air and steam. Steam increased creep rates and reduced fiber lifetimes. Fiber microstructures were characterized by TEM. The small amounts of grain growth, fiber-axis grain elongation, and pore growth that occur during creep were quantified. To separate the effects of stress and temperature on microstructural evolution, grain growth and elongation were also quantified for fibers heat-treated for 1–100 h in air at 1100–1500 °C. Grain growth laws were determined. The contributions of pore growth and grain elongation to creep strain were quantified. Grain elongation accounts for a large fraction of the strain during creep in air, but little in steam. Pore growth was more pronounced in steam, but does not create significant creep strain. Creep and failure mechanisms consistent with the observed microstructural changes are discussed.