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Thermal Cycling Behavior of Thermal Barrier Coatings with MCrAlY Bond Coat Irradiated by High-Current Pulsed Electron Beam

Cai, Jie, Lv, Peng, Guan, Qingfeng, Xu, Xiaojing, Lu, Jinzhong, Wang, Zhiping, Han, Zhiyong
ACS applied materials 2016 v.8 no.47 pp. 32541-32556
air, aluminum oxide, bubbles, coatings, cracking, deformation, delamination, irradiation, nanoparticles, spraying
Microstructural modifications of a thermally sprayed MCrAlY bond coat subjected to high-current pulsed electron beam (HCPEB) and their relationships with thermal cycling behavior of thermal barrier coatings (TBCs) were investigated. Microstructural observations revealed that the rough surface of air plasma spraying (APS) samples was significantly remelted and replaced by many interconnected bulged nodules after HCPEB irradiation. Meanwhile, the parallel columnar grains with growth direction perpendicular to the coating surface were observed inside these bulged nodules. Substantial Y-rich Al₂O₃ bubbles and varieties of nanocrystallines were distributed evenly on the top of the modified layer. A physical model was proposed to describe the evaporation–condensation mechanism taking place at the irradiated surface for generating such surface morphologies. The results of thermal cycling test showed that HCPEB-TBCs presented higher thermal cycling resistance, the spalling area of which after 200 cycles accounted for only 1% of its total area, while it was about 34% for APS-TBCs. The resulting failure mode, i.e., in particular, a mixed delamination crack path, was shown and discussed. The irradiated effects including compact remelted surface, abundant nanoparticles, refined columnar grains, Y-rich alumina bubbles, and deformation structures contributed to the formation of a stable, continuous, slow-growing, and uniform thermally grown oxide with strong adherent ability. It appeared to be responsible for releasing stress and changing the cracking paths, and ultimately greatly improving the thermal cycling behavior of HCPEB-TBCs.