Revealing the oxidation growth mechanism and crack evolution law of Si-HfO2/Yb2Si2O7/Yb2SiO5/high-entropy hafnate thermal/environmental barrier coatings during thermal cycling
Ruixiang Liu, Wenping Liang, Qiang Miao, Hui Zhao, Xiaofeng Zhang, Shijie Sun, Feilong Jia, Kai Zang, Rongxue Yan, Xiaoqi Tan, Qijia Liu, Min Wu
Abstract
The Si-HfO 2 /Yb 2 Si 2 O 7 /Yb 2 SiO 5 /(Dy 0.2 Ho 0.2 Er 0.2 Tm 0.2 Lu 0.2 ) 2 Hf 2 O 7 thermal/environmental barrier coating (T/EBC) protects ceramic matrix composites (CMCs) from turbine multi-corrosive media erosion. Challenges persist in the thermal cycling performance of multi-layered T/EBC, notably in understanding the oxidation of the Si-HfO 2 bond coat, compatibility of its mixed thermally grown oxide (m-TGO) with adjacent layers, and the evolution of cracks caused by thermal cycling. Utilizing plasma spraying physical vapor deposition (PS-PVD), this T/EBC on CMC substrates withstands up to 200 hours at 1450 ℃ to 1550 ℃. The m-TGO oxidation follows a parabolic growth curve , with oxygen diffusion activation energies of 160.31 kJ/mol from 1450 ℃ to 1500 ℃, and 125.16 kJ/mol from 1500 ℃ to 1550 ℃. Thermo-mechanical calculations indicate that elastic strain energy accumulation causes interlaminar cracks between m-TGO and adjacent layers. Controlling mud crack density is key to preventing the stress attraction at the tips of bifurcated cracks, thereby avoiding the formation of interlaminar cracks.