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Transmission electron microscopy on Zr- and Hf-borides with MoSi2 addition: Densification mechanisms

Published online by Cambridge University Press:  31 January 2011

Laura Silvestroni ,
Hans-Joachim Kleebe ,
Stefan Lauterbach ,
Mathis Müller  and
Diletta Sciti
Laura Silvestroni*
Affiliation:
National Council of Research–Institute of Science and Technology for Ceramics (CNR-ISTEC), I-48018 Faenza, Italy
Mathis Müller
Affiliation:
Technical University of Darmstadt–Institute of Applied Geosciences (TUD-IAG), D-64287 Darmstadt, Germany
Diletta Sciti
Affiliation:
National Council of Research–Institute of Science and Technology for Ceramics (CNR-ISTEC), I-48018 Faenza, Italy
*
a)Address all correspondence to this author. e-mail: laura.silvestroni@istec.cnr.it
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Abstract

The microstructures of two pressureless sintered ceramics, ZrB2 and HfB2 with 20 vol% MoSi2 added, were analyzed by scanning and transmission electron microscopies. Carbides and oxides of the transition metals and MoB were observed to be well dispersed within the boride matrix. Mo5Si3 and Mo5SiB2, with Zr or Hf impurities, were observed at triple grain junctions and showed a partial wetting of the matrix. It was also noticed that the borides had a core-shell structure, which was especially pronounced in the ZrB2-based composite. The experimental results suggest the formation of a Mo–Si–B liquid phase at high temperature, which strongly promoted the densification. The densification mechanisms are discussed in light of the microstructure evolution on sintering, thermodynamic considerations, and the phase diagrams of the species involved.

Keywords

DensificationMicrostructureTransmission electron microscopy (TEM)
Type
Articles
Information
Journal of Materials Research , Volume 25 , Issue 5 , May 2010 , pp. 828 - 834
Copyright
Copyright © Materials Research Society 2010

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