resumo
Eutectic and off-eutectic mullite-zirconia fibres were grown by LFZ (laser floating zone) directional solidification. The microstructure of the mullite-zirconia eutectic fibres varies from planar coupled eutectic (1 mm/h pulling rate) through mullite columnar growth with coarse zirconia inclusions (10 mm/h pulling rate) to faceted mullite eutectic dendrites, which enclose a dispersion of fine zirconia fibrils (100-500 mm/h pulling rates). Near-equilibrium conditions determine the crystallization of monoclinic zirconia and the absence of any amorphous phase, whereas for higher speeds the tetragonal structure is retained and a residual liquid is kept after the eutectic solidification. Similar structural and morphological characteristics are displayed by the mullite-rich off-eutectic composition added to the development of prismatic crystals of mullite primary phase. In opposition, heavy constitutional supercooling takes place in the case of the zirconia-rich off-eutectic fibres, where equiaxed zirconia dendrites soon form as a primary phase, leaving a non-equilibrium mixture of alumina and sillimanite as interdendritic constituent. (C) 2012 Elsevier Ltd. All rights reserved.
palavras-chave
FLOATING-ZONE TECHNIQUE; GROWN AL2O3-ZRO2(Y2O3) EUTECTICS; MECHANICAL-PROPERTIES; RESIDUAL-STRESSES; CERAMICS; AL2O3-ZRO2-SIO2; MICROSTRUCTURE; Y2O3-ZRO2; STABILITY; COMPOSITE
categoria
Materials Science
autores
Carvalho, RG; Pires, MS; Fernandes, AJS; Silva, RF; Costa, FM
nossos autores
Rui Ramos Ferreira e Silva
Professor associadoagradecimentos
Ricardo Carvalho thanks to Fundacao para a Ciencia e a Tecnologia (FCT) for the financial funding SFRH/BD/64891/2009 and PEst-C/CTM/LA0025/2011.