Relation between Process, Microstructure and Mechanical Properties of a continuous ceramic fiber under development
Topic(s) : Material science
Co-authors :
Juliette REDONNET (FRANCE), Olivier FRANCY , Marie-Hélène BERGER , Sébastien JOANNÈS (FRANCE), Stephanie PFEIFER , Bernd CLAUSS (GERMANY)Abstract :
Oxide Ceramic Matrix Composites (OCMC) are the best candidates to replace metal alloys working at intermediate temperatures and in extreme environments such as in gas turbines. The development of OCMC highly depends on the availability of continuous oxide ceramic fibers with high mechanical properties. No continuous weavable oxide fiber is currently produced and marketed in Europe, the market being dominated by USA and soon China.
The present study is part of a collaboration between Mines Paris – PSL, Saint-Gobain Research Provence and the DITF (Deutsch Institute für Textil and Faserforschung). The DITF produces at a pilot scale a continuous alumina fiber showing very promising results. Saint-Gobain has established a collaboration with the DITF for the joint development and manufacture of European continuous oxide ceramic fibers. The Centre des Matériaux of Mines Paris - PSL University has more than forty years of experience in the microstructural and mechanical characterization of fibers.
To develop an alumina fiber with thermo-mechanical properties reaching required specifications for OCMC, the relationship between the manufacturing process parameters, the microstructure of the fibers and their mechanical properties must be fully understood and controlled.
The flexibility of ceramic fibers of high elastic modulus is possible thanks to fiber diameters no larger than 10 µm. The high strength of a fiber is provided by a dense nano-scale microstructure and a controlled intergranular chemistry, together with a precise control of the size and dispersion of critical defects.
The work presented has focused on microstructure characterization by SEM and TEM down to atomic scale of these alumina fiber, in relationship with tensile tests carried out on single fibers and bundles and coupled with acoustic emission analysis. Critical defects were characterized so as to identify the origin of their formation during the process and improve of the performance of this alumina fiber through an optimization of its manufacture parameters.
Two types of defects have been distinguished. The first type consists in defects of less than 100 nm in size homogeneously distributed in the fibers and developed during the transformation of the precursor into alpha alumina, such as intergranular or intragranular porosity or second phase, incomplete conversion from transition alumina to alpha alumina or vermicular structure. The second type corresponds to isolated and heterogeneously distributed defects larger than 100 nm such as surface defects, larger pores or volume defects in the fiber. These defects are responsible for the fiber failure and the large dispersion of failure stresses.
The present study is part of a collaboration between Mines Paris – PSL, Saint-Gobain Research Provence and the DITF (Deutsch Institute für Textil and Faserforschung). The DITF produces at a pilot scale a continuous alumina fiber showing very promising results. Saint-Gobain has established a collaboration with the DITF for the joint development and manufacture of European continuous oxide ceramic fibers. The Centre des Matériaux of Mines Paris - PSL University has more than forty years of experience in the microstructural and mechanical characterization of fibers.
To develop an alumina fiber with thermo-mechanical properties reaching required specifications for OCMC, the relationship between the manufacturing process parameters, the microstructure of the fibers and their mechanical properties must be fully understood and controlled.
The flexibility of ceramic fibers of high elastic modulus is possible thanks to fiber diameters no larger than 10 µm. The high strength of a fiber is provided by a dense nano-scale microstructure and a controlled intergranular chemistry, together with a precise control of the size and dispersion of critical defects.
The work presented has focused on microstructure characterization by SEM and TEM down to atomic scale of these alumina fiber, in relationship with tensile tests carried out on single fibers and bundles and coupled with acoustic emission analysis. Critical defects were characterized so as to identify the origin of their formation during the process and improve of the performance of this alumina fiber through an optimization of its manufacture parameters.
Two types of defects have been distinguished. The first type consists in defects of less than 100 nm in size homogeneously distributed in the fibers and developed during the transformation of the precursor into alpha alumina, such as intergranular or intragranular porosity or second phase, incomplete conversion from transition alumina to alpha alumina or vermicular structure. The second type corresponds to isolated and heterogeneously distributed defects larger than 100 nm such as surface defects, larger pores or volume defects in the fiber. These defects are responsible for the fiber failure and the large dispersion of failure stresses.