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Formation of in situ Reinforced Microstructures in α-sialon Ceramics: Part II. In the Presence of a Liquid Phase

Published online by Cambridge University Press:  31 January 2011

Hong Peng ,
Zhijian Shen  and
Mats Nygren
Hong Peng
Affiliation:
Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91, Stockholm, Sweden
Zhijian Shen*
Affiliation:
Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91, Stockholm, Sweden
Mats Nygren
Affiliation:
Department of Inorganic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91, Stockholm, Sweden
*
a)Address all correspondence to this author. e-mail: shen@inorg.su.se
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Extract

In situ reinforced microstructures with well-dispersed elongated grains, up to 10 μm in length, embedded in matrices consisting of submicron equiaxed grains, were developed by hot pressing Y-, Yb-, and (Y + Yb)-doped a-sialon ceramics containing approximately 3 vol% extra liquid phase at a comparatively low sintering temperature, 1800 °C. The liquid phase, thermodynamically compatible with a-sialon, was introduced by raising the oxygen content of an already oxygen-rich α-sialon composition, e.g., by increasing the O/N ratio in RExSi12-(3x+n) Al3x+nOnN16−n. Two different α–Si3N4 precursor powders, one fine-grained and one coarse, and one coarse β–Si3N4 powder were used, and the influence of particle size and crystalline modification of the precursor Si3N4 powder on the formation of elongated a-sialon grains was investigated. The formation of elongated α-sialon grains was promoted by introducing an extra liquid phase and by using a fine-grained α–Si3N4 powder, whereas the coarse β–Si3N4 powder did not yield any elongated grains at all. The obtained in situ reinforced α-sialon ceramics were both hard and tough, with a Vickers hardness and a fracture toughness of 21 GPa and approximately 5 MPa m1/2, respectively.

Type
Articles
Information
Journal of Materials Research , Volume 17 , Issue 5 , May 2002 , pp. 1136 - 1142
Copyright
Copyright © Materials Research Society 2002

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