Chapter 6. Grain Boundary Chemistry of SiC-Based Armor
- Lisa Prokurat,
- Andrew Wereszczak,
- Edgar Lara-Curzio
Published Online: 26 MAR 2008
Copyright © 2007 The American Ceramics Society
Advances in Ceramic Armor II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 7
How to Cite
Pabit, E., Siebein, K., Butt, D. P., Heinrich, H., Ray, D., Kaur, S., Flinders, R. M. and Cutler, R. A. (2008) Grain Boundary Chemistry of SiC-Based Armor, in Advances in Ceramic Armor II: Ceramic Engineering and Science Proceedings, Volume 27, Issue 7 (eds L. Prokurat, A. Wereszczak and E. Lara-Curzio), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291368.ch6
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 2006
Print ISBN: 9780470080573
Online ISBN: 9780470291368
- precracked beam;
- electron microscopy;
- grain boundary;
- aluminum-containing samples;
Fourteen SiC-based materials were processed by hot pressing. The single-edge precracked beam (SEPB) fracture toughness varied from 2.4 to 6.8 MPa-m1/2 and fracture modes changed from transgranular to intergranular. Grain boundaries and triple points were analyzed using high-resolution transmission electron microscopy combined with energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) using an energy-filtered approach. The objective of this study was to compare the grain boundary chemistry of these materials and determine how it affected fracture mode.
In all samples containing Al, AlN or Al2O3, oxygen was associated with aluminum at the grain boundaries. Chemical analysis of the hot pressed bulk material showed that O levels ranged between 0.3 and 1.1 wt. %, whereas N levels were as high as 1.5 %. In all of the aluminum-containing samples, the Al and O concentrated at triple points and penetrated along most grain boundaries regardless of the fracture mode. Nitrogen in the AIN-doped samples was difficult to detect by EDS or EELS at 2200°C, suggesting that it diffused into the 4H or 6H polytypes during sintering. Likewise, it was generally difficult to detect the O or Al in solid solution within the SiC grains.
Simultaneous boron and carbon additions lowered the fracture toughness when either Al or A1N were used at the same cation content. Triple point and grain boundary chemistries, however, were similar to those where no B and C were added. This was primarily due to the enhanced early densification, which resulted in higher amounts of O and N in these compositions. Quantitative fracture mode did not correlate with grain size and grain boundary chemistry, as had been expected.