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Directionally Solidified Mullite Fibers

Published online by Cambridge University Press:  15 February 2011

Ali Sayir  and
Serene C. Farmer
Ali Sayir
Affiliation:
NASA Lewis Research Center, Cleveland, Ohio 44135Case Western Reserve University
Serene C. Farmer
Affiliation:
NASA Lewis Research Center, Cleveland, Ohio 44135
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Abstract

Directionally solidified fibers with nominal mullite compositions of 3Al2O3·2SiO2 were grown by the laser heated float zone (LHFZ) method at NASA Lewis. High resolution digital images from an optical microscope evidence the formation of a liquid-liquid miscibility gap during crystal growth. Experimental evidence shows that the formation of mullite in aluminosilicate melts is in fact preceded by liquid immiscibility. The average fiber tensile strength is 1.15 GPa at room temperature. The mullite fibers retained 80 % of their room temperature tensile strength at 1450 °C. SEM analysis revealed that the fibers were strongly faceted and that the facets act as critical flaws. Examined in TEM, these mullite single crystals are free of dislocations, low angle boundaries and voids. Single crystal mullite showed a high degree of oxygen vacancy ordering. Regardless of the starting composition, the degree of order observed in polycrystalline fibers was lower than that observed in the mullite single crystals.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 365: Symposium M – Ceramic Matrix Composites–Advanced High-Temperature Structural Materials , 1994 , 11
Copyright
Copyright © Materials Research Society 1995

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