Durability of YSZ coated Ti₂AlC in 1300°C high velocity burner rig tests

Abstract

A thermal barrier coating (TBC) system survived 500 hours in aggressive, 1300°C burner rig testing. The yttria-stabilized zirconia (7YSZ) TBC was plasma sprayed on an oxidation-resistant Ti 2 AlC-type MAX phase and tested in a jet fuel burner at 100 m/s, using 5 hours cycles. No coating spallation or surface recession was observed; Al 2 O 3-scale growth produced a slight 2.4 mg/cm 2 mass gain. The coating surface exhibited craze-cracked colonies of [111] flourite textured columns, with no visible moisture attack. The 20 μm alumina scale remained intact under the YSZ face, about twice that producing failure for TBC/superalloy systems. TiO 2 nodules, initially formed on the uncoated backside, were removed, and Al 2 O 3 was etched through volatile hydroxides formed in water vapor (~10%). Overall, the test indicated exceptional stability of the YSZ/Al 2 O 3 /Ti 2 AlC system under turbine conditions due in large part to close thermal expansion matching.

Relative Ti2AlC Scale Volatility under 1300 °C Combustion Conditions

“…The platelets retained a slight Ti level; they may have been derived from TiAl2O5 grains where Ti was removed by selective water vapor corrosion. Xrd analyses of the oxidized surface showed ~10% TiO2 after the initial 20 min at 1000 °C, then removed by volatile reactions to just 0.1% after the 1300 °C exposure, the remainder of the scale being α-Al2O3 [15]. No phase change in the Ti2AlC substrate was apparent other than reduced x-ray diffraction intensity due to absorption from the thickening scale.…”

“…Phase contents were estimated from (Brüker 8D) X-ray diffractometer scans and Rietveld refinement, using Jade software (version 6). Complete experimental details are available in the source studies [12][13][14][15].…”

“…Part of the motivation relates to the behavior of Al 2 O 3 scales in high velocity water vapor at 1300 • C, an environment not typically used for standard metal alloy tests. The materials and processes were described in detail from a number of studies comprising the source data for this compilation [12][13][14][15]. All the results subsequently presented derive from these studies.…”

“…Cubic oxidation kinetics suggested by linearized transient-corrected weight vs t 1/3 behavior for Ti2AlC. (a) 6 atm, 25 m/s, 50 h, HP-BRT; and (b) 1 atm., 100 m/s, 500 h, Mach 0.3 BRT, with YSZ face-coat[13,15].…”

“…SEM/BSE surface microstructures of scales formed on Ti2AlC at 1300 °C in Mach 0.3 high velocity burner rig (500 h at 1300 °C) Uncoated backside at sample (a) top, (b) hot center, (c) grip end. T (Ti-rich transient scale); A (Al2O3); P (etched platelets)[15].…”