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Here we consider our four-point flexure and compression creep results obtained under Ar protection at 1800 ℃ to predict the tensile creep behavior of a ZrB2-20 vol% SiC ultra-high temperature ceramic. Assuming power law creep, and based on four-point bend data, we estimated the uniaxial creep parameters using an analytical method present in the literature. Both predicted and experimental compressive stress exponents were found to be in excellent agreement, 1.85 and 1.76 respectively, while observation of the microstructure suggested a combination of diffusion and grain boundary sliding creep mechanisms in compression. Along with the microstructural evidence associated with the tensile regions of the flexure specimens, the predicted tensile stress exponent of 2.61 exceeds the measured flexural value of 2.2. We assert an increasing role of cavitation to the creep strain in pure tension. This cavitation component adds to the dominant grain boundary sliding mechanism as described below and elsewhere for flexural creep.


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Prediction of tensile power law creep constants from compression and bend data for ZrB2-20 vol% SiC composites at 1800 °C

Show Author's information Ali KHADIMALLAH( )Marc W. BIRDKenneth W. WHITE
Department of Mechanical Engineering, University of Houston, Houston, TX, USA

Abstract

Here we consider our four-point flexure and compression creep results obtained under Ar protection at 1800 ℃ to predict the tensile creep behavior of a ZrB2-20 vol% SiC ultra-high temperature ceramic. Assuming power law creep, and based on four-point bend data, we estimated the uniaxial creep parameters using an analytical method present in the literature. Both predicted and experimental compressive stress exponents were found to be in excellent agreement, 1.85 and 1.76 respectively, while observation of the microstructure suggested a combination of diffusion and grain boundary sliding creep mechanisms in compression. Along with the microstructural evidence associated with the tensile regions of the flexure specimens, the predicted tensile stress exponent of 2.61 exceeds the measured flexural value of 2.2. We assert an increasing role of cavitation to the creep strain in pure tension. This cavitation component adds to the dominant grain boundary sliding mechanism as described below and elsewhere for flexural creep.

Keywords:

power law creep parameters, four-point flexure, compression, tension, creep mechanisms
Received: 12 January 2017 Revised: 31 July 2017 Accepted: 22 August 2017 Published: 19 December 2017 Issue date: December 2017
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Publication history
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Publication history

Received: 12 January 2017
Revised: 31 July 2017
Accepted: 22 August 2017
Published: 19 December 2017
Issue date: December 2017

Copyright

© The author(s) 2017

Acknowledgements

The authors gratefully acknowledge AFOSR program monitor Ali Sayir, under grant # FA9550-09-1-0200, for partial support of this work. Extended appreciation goes to Dr. Pradeep Sharma for insightful comments that greatly improved this manuscript and Dr. Bill Fahrenholtz, Dr. Greg Hilmas, and Mr. Eric Neuman at the Missouri University of Science and Technology, Rolla, MO, USA, for providing the materials used in this study.

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