Mechanical behaviour of zirconia–mullite directionally solidified eutectics

•Directionally solidified ZrO2-mullite eutectic grown by laser floating zone.•Ultra-fine eutectic morphology.•A remarkable hardness value of 21.2GPa for the fastest as-grown fibres. Laser floating zone technique (LFZ) is used to grow directionally solidified eutectic (DSE) zirconia–mullite composite...

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Bibliographic Details
Published in:Materials in engineering 2014-09, Vol.61, p.211-216
Main Authors: Carvalho, R.G., Oliveira, F.J., Silva, R.F., Costa, F.M.
Format: Article
Language:English
Subjects:
Directional solidification
Fibres
Mechanical properties
Mullite
Zirconia
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Summary:•Directionally solidified ZrO2-mullite eutectic grown by laser floating zone.•Ultra-fine eutectic morphology.•A remarkable hardness value of 21.2GPa for the fastest as-grown fibres. Laser floating zone technique (LFZ) is used to grow directionally solidified eutectic (DSE) zirconia–mullite composite fibres (30:70 in wt.%). A notable increase in hardness is observed from 11.3 to 21.2GPa as the pulling rate increases from 10 to 500mm/h, due to the ultra-fine eutectics developed at very high growth rates. The indentation fracture toughness reaches a maximum value of 3.5MPam1/2 for the fibre pulled at 100mm/h, almost three times the value of 1.2MPam1/2 determined for LFZ single-crystal mullite. The eutectic dendrites that develop along the growth direction are immersed in a glassy phase whose brittleness is counteracted by the beneficial ultra-fine morphology, giving a bending strength maximum of 534MPa. Yet, the soft nature of the glassy matrix prevails at the high temperature testing (1400°C), causing a decrease to about one-half of the RT value in the fibres with less glassy phase content.
ISSN:0261-3069
DOI:10.1016/j.matdes.2014.04.050