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Effect of In Situ-Formed Cerium Hexaaluminate Precipitates on Properties of Alumina -24 Vol% Zirconia (1.4Y) Composites
F. Kern
University of Stuttgart, IFKB, Allmandring 7B, D-70569 Stuttgart, Germany
received May 14, 2013, received in revised form June 18, 2013, accepted August 5, 2013
Vol. 4, No. 4, Pages 177-186 DOI: 10.4416/JCST2013-00014
Abstract
In situ-platelet-reinforced zirconia-toughened alumina ceramics have become established materials, successfully replacing alumina and zirconia in hip implants. While the beneficial effect of the in situ toughening seems undoubted, this toughening mechanism is still not fully understood.
A nanocomposite ZTA containing 24 vol% partially stabilized zirconia (1.4Y-TZP) was reinforced with 10 vol% cerium hexaaluminate (CA6) by reacting in situ-reduced ceria with alumina during hot pressing. The mechanical properties, evolution of microstructure and phase composition of the CA6-containing ZTA were compared with the properties of the non-reinforced reference.
The unreinforced ZTA24 shows a microstructure with modular matrix grains and ultrafine zirconia dispersion. High strength of 1150 MPa but moderate toughness of 5 MPa·√m and low transformability of the zirconia dispersion was observed. The CA6-reinforced material shows higher toughness and transformability combined with a trade-off in hardness and strength. The CA6 precipitates are rod-shaped, well dispersed and oriented normal to the pressing direction. The formation of CA6 especially at sintering temperatures exceeding 1500 °C is associated with microstructural coarsening and a broadening of grain size distribution of matrix and dispersion, making the zirconia more transformable. Crack deflection at matrix-precipitate grain boundaries was not observed.
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Keywords
Alumina, zirconia, platelets, mechanical properties, microstructure
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