Environmental resistance of a Ti₂AlC-type MAX phase in a high pressure burner rig

Authors

James L. Smialek Ph.D., NASA Glenn Research CenterFollow

Date of this Version

2017

Citation

Journal of the European Ceramic Society 37 (2017) 23–34

Comments

U.S. Government Work

Abstract

Alumina-forming commercial Ti₂AlC (MAXthal 211)^TM phase samples were exposed in a jet fueled, high pressure burner rig (HPBR) at 1100◦, 1200◦, and 1300◦C, operating at 6 atm (bar) and 25 m/s, in ∼10%water vapor. Weight change exhibited a rapid initial uptake associated with a TiO₂ transient phase followed by cubic kinetics of a slow-growing α-Al₂O₃underlayer. The cubic rate constants, kc, were approximately 20% of those measured in static thermo-balance furnace tests. A small recession rate of −0.012 mg/cm²/h was measured at 1300◦C for a pre-oxidized sample. The loss rate was ∼15% that observed for SiO2scales subject to volatile Si(OH)4formation for SiC tested under similar conditions.These kinetic features were fitted in a modified cubic-linear law. From thermodynamic, XRD, and SEM analyses, it is proposed that volatile TiO(OH)₂ was formed by the reaction of water vapor with TiO₂ and TiAl₂O₅ outer layers.