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

Abstract

Alumina-forming commercial Ti2AlC (MAXthal 211)™ phase samples were exposed in a jet-fueled, high pressure burner rig (HPBR) at 1100°, 1200°, and 1300°C, operating at 6atm (bar) and 25m/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-Al2O3 underlayer. The cubic rate constants, kc, were approximately 20% of those measured in static thermo-balance furnace tests. A small recession rate of −0.012mg/cm2/h was measured at 1300°C for a pre-oxidized sample. The loss rate was ∼15% that observed for SiO2 scales subject to volatile Si(OH)4 formation 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.