Stress Evolution and Element Diffusion in Bi-Layered Yb_2SiO_5/Mullite Environmental Barrier Coatings under High-Temperature Molten Salt Corrosion

摘要

Yb_2SiO_5/mullite bi-layered coatings are promising environmental barrier coatings, but its molten salt corrosion mechanism is unclear. In this work, Yb_2SiO_5/mullite bi-layered coatings are fabricated by combining plasma spraying and dip-coating techniques. Residual stresses in the coatings caused by thermo-mechanical interaction are investigated by a nondestructive Raman spectrum method under high-temperature molten salt corrosion. In the as-deposited coatings, the stress in the mullite layer is compressive and the value near Si_3N_4 substrate is minimum. During high-temperature corrosion test, the residual stress near mullite-substrate interface changes sharply while the stress near mullite-Yb_2SiO_5 interface is concentrated without large fluctuation. An interfacial phase, YbAlO_3, which is formed because of the inter diffusion of Al in the mullite layer and Yb in the Yb_2SiO_5 layer, causes the stress concentration. The change of SiO_2 component in the mullite layer leads to the sharp change of residual stress near the mullite-substrate interface.