Relative Ti2AlC Scale Volatility under 1300 °C Combustion Conditions

Abstract

Turbine environments may degrade high temperature ceramics because of volatile hydroxide reaction products formed in water vapor. Accordingly, the volatility of transient TiO2 and steady-state Al2O3 scales formed on the oxidation-resistant Ti2AlC MAX phase ceramic was examined in 1300 °C high velocity (Mach 0.3, 100 m/s) and high pressure (6 atm, 25 m/s) burner rig tests (BRT). Unlike metals, the ceramic was stable at 1300 °C. Unlike SiC and Si3N4, neither burner test produced a weight loss, unless heavily pre-oxidized. Lower mass gains were produced in the BRT compared to furnace tests. The commonly observed initial, fast TiO2 transient scale was preferentially removed in hot burner gas (~10% water vapor). A lesser degree of gradual Al2O3 volatilization occurred, indicated by grain boundary porosity and crystallographic etching. Modified cubic-linear (growth-volatility) kinetics are suggested. Gas velocity and water vapor pressure play specific roles for each scale. Furthermore, a 7YSZ TBC on Ti2AlC survived for 500 h in the Mach 0.3 burner test at 1300 °C with no indication of volatility or spalling.

Simplified Paralinear Oxidation Analyses

“…Burner rig results for 1300°C tests at 25 m/s, 6 atm., (HP-BRT), and 100 m/s, 1 atm., (HV-BRT), are shown in Fig. 10, (from Smialek [10]). They show the measured burner data to be considerably lower than furnace (quiet air) data.…”

“…Initially this COSP approach successfully described the cubic (growth)-linear (volatility) kinetics of MAX phase Ti 2 AlC materials in high pressure and high velocity burner rigs (in Smialek 2020). [10]. The purpose of the present study is to determine whether k p and k l results extracted via the COSP strategy produce the same values obtained from more classic analyses of published Cr, NiCr, Pb, SiC, Si 3 N 4 , and BN paralinear behaviors.…”

“…2 and Al 2 O 3 scales, Smialek 2020[10], the latter for SiO 2 exposed to aggressive burner rig tests, Robinson/Smialek 1999[13], Yuri/Hisamatsu, etc. 2003][14] …”

Effects of pellet surface roughness and pre-oxidation temperature on CMAS corrosion behavior of Ti2AlC

“…The scanning rate is 0.2 (°)/s, and the scanning range is 10°-80°. The X-ray diffraction (XRD) diagrams were refined with the Rietveld method using the MDI Jade 9 software package, and the phase contents were calculated [29]. For the Al 2 O 3 , TiO 2 , and Ti 2 AlC phases, the space groups used for Rietveld refinement were R-3c (167), P42/mnm (136), and P63/mmc (194), respectively.…”

Special Issue: Environmental Barrier Coatings

“…The nine research articles in this special issue present recent advances in EBC technology in the following areas: recession [14]; EBC chemistry and processes [15,16]; oxidation and recession [17]; oxygen permeability and EBC design [18]; CMAS thermal and mechanical properties [19]; CMAS infiltration modeling [20]; mechanical behavior in thermal shock [21]; and thermomechanical reliability: modeling and validation [22].…”