Tensile and creep performance of a novel mullite fiber at high temperatures

The novel fiber CeraFib75 with a composition near to pure mullite was analyzed with respect to its potential for high-temperature applications. This mullite fiber free of glass phase was aimed to overcome the strength of commercial oxide fibers at high-temperatures. Tensile tests at room and high temperatures ranging from 900 to 1400 °C and creep tests were performed. Nextel™720, another crystalline mullite-alumina fiber, was tested as a reference. Microstructure and crystal phase analysis of the new fiber revealed mullite grains with traces of γ- and α-alumina in-between; it contains occasionally defects causing a reduced strength at room-temperature. Remarkably, at temperatures beyond 1200 °C, CeraFib75 presented a higher tensile strength than Nextel™720. During tensile tests at 1400 °C, an extended region of inelastic deformation was observed for CeraFib fibers only, which was related to a grain boundary sliding mechanism. Creep rates were of the same order of magnitude for both fibers.