Preparation and properties of aluminium titanate-alumina composites with a corrugated microstructure
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peated deformation processing was used to produce layered aluminium titanate (ATI)-alumina composites with a corrugated microstructure. Viscous nonpolar pastes of ATI and alumina powders were prepared using paraffin oil as the dispersing medium. These pastes were rolled into tapes 1 mm thick, which were then stacked together to form starting bi-material laminates in an A-B-A sequence. The laminates were then plastically deformed by repeated folding and rolling at room temperature. After a sufficiently large true plastic deformation, composites with corrugated microstructures were successfully produced. During sintering, part of the ATI decomposed; in the alumina layers large anisotropic grains were formed. The mechanical properties of the sintered composites improved with structural refinement, in spite of extensive microcracking observed during cooling from the sintering temperature. In addition, the thermal expansion coefficient along the rolling direction did not differ from that of the reference material.
I. INTRODUCTION
Sintered aluminium titanate (ATI) ceramics exhibit attractive thermal properties, such as a low thermal expansion coefficient and high thermal shock resistance, but their use in practice is limited because of poor mechanical strength.1 This is because of extensive microcracking, which occurs during cooling due to the large thermal anisotropy of the ATI grains.2 Up to 50% higher strength values were reported with particulate ATI-alumina composites, though at the expense of a higher thermal expansion coefficient and lower thermal shock resistance.3 The changes in the composites’ properties arise mainly because of the prevention of ATI microcracking due to a decreased ATI grain size in the presence of secondary particles. With appropriate composite microstructures in which ATI grain growth is not inhibited, the ATI-based composites could have improved mechanical properties and at the same time retain the thermal properties of the matrix ATI ceramics. The possible candidates could be laminated composites in which ATI grain growth is not inhibited by the presence of secondary particles. However, there is no literature data for ATI-alumina laminated composites, most probably due to sintering mismatch between these two powders.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0051 448
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 2, Feb 2006 Downloaded: 15 Mar 2015
Recently a new type of layered ceramic-matrix composite was developed, which differs from conventional laminates in that the interface has a tendency to be wavy and in part discontinuous, with a globular or elongated second phase within a continuous matrix phase.4 Due to their structure, these composites show an improved sinterability. Interface instability induced during repeated plastic deformation of the starting pastes creates corrugated interfaces with a large layer waviness that reduces long-range sintering stress.5 The better sinterability is also reflected in the im
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