Title

Grain Boundary Chemistry Of Sic-Based Armor

Abstract

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 AlN-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 AlN 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.

Publication Date

12-1-2006

Publication Title

Ceramic Engineering and Science Proceedings

Volume

27

Issue

7

Number of Pages

69-84

Document Type

Article; Proceedings Paper

Personal Identifier

scopus

Socpus ID

33845955228 (Scopus)

Source API URL

https://api.elsevier.com/content/abstract/scopus_id/33845955228

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