Oxidation of TaSi2-Containing ZrB2-SiC Ultra-High Temperature Materials~!2009-09-08~!2009-12-23~!2010-04-20~!

Abstract

Hot pressed coupons of composition ZrB2 -20 v% SiC -5 v% TaSi2 and ZrB 2 -20 v% SiC -20 v% TaSi2 were oxidized in stagnant air at temperatures of 1627 and 1927C for one, five and ten 10-minute cycles. The oxidation reactions were characterized by weight change kinetics, x-ray diffraction, and SEM/EDS. Detailed WDS/microprobe quantitative analyses of the oxidation products were conducted for the ZrB 2 -20 v% SiC -20 v% TaSi2 sample oxidized for five 10-minute cycles at 1927C. Oxidation kinetics and product formation were compared to ZrB 2 -20 v% SiC with no TaSi2 additions. It was found that the 20 v% TaSi 2 composition exhibited improved oxidation resistance relative to the material with no TaSi2 additions at 1627C. However, for exposures at 1927C less oxidation resistance and extensive liquid phase formation were observed compared to the material with no TaSi 2 additions. Attempts to limit the liquid phase formation by reducing the TaSi2 content to 5 v% were unsuccessful. In addition, the enhanced oxidation resistance at 1627C due to 20 v% TaSi2 additions was not achieved at the 5 v% addition level. The observed oxidation product evolution is discussed in terms of thermodynamics and phase equilibria for the TaSi2-containing ZrB 2 -SiC material system. TaSi2-additions to ZrB2-SiC at any level are not recommended for ultra-high temperature (>1900C) applications due to excessive liquid phase formation.

Combined effects of WC and SiC on densification and thermo-mechanical stability of ZrB2 ceramics

“…Additional third phases able to bring benefit to the high temperature performance of MeB2-SiC systems include carbides and silicides of W, Ta, or Mo [3,[10][11][12][13]. In this respect, the incorporation of WC has recently gained great attention thanks to an attractive ability claimed by some authors [10,14,15] to favour the flexure strength retention at temperatures up to 1600°C.…”