Abstract
Crack healing phenomena were observed in mullite and mullite + Yb2SiO5 environmental barrier coating (EBC) materials during thermal shock cycles. Air plasma spray coating was used to deposit the EBC materials onto a Si bondcoat on a SiCf/SiC composite substrate. This study reveals that unidirectional vertical cracks (mud cracks) formed after several thermal shock cycles; however, the cracks were stable for 5000 thermal shock cycles at a maximum temperature of 1350 °C. Moreover, the crack densities decreased with an increasing number of thermal shock cycles. After 3000 thermal shock cycles, cracks were healed via melting of a phase containing SiO2 phase, which partially filled the gaps of the cracks and resulted in the precipitation of crystalline Al2O3 in the mullite. Post-indentation tests after thermal shock cycling indicated that the mullite-based EBC maintained its initial mechanical behavior compared to Y2SiO5. The indentation load–displacement tests revealed that, among the materials investigated in the present study, the mullite + Yb2SiO5 EBC demonstrated the best durability during repetitive thermal shocks.
Highlights
Gas turbines that operate at high temperatures are being developed for and installed in stationary and aviation applications
The cracks formed on the surface and cross section of the environmental barrier coating (EBC) coating layer by thermal shock were
We considered that these cracks developed because ofEBC
Summary
Gas turbines that operate at high temperatures are being developed for and installed in stationary and aviation applications. All-ceramic materials are likely to be used for hot gas components such as combustor liners, blades, and nozzles, which require durable materials that can withstand high temperatures. Silicon carbide exhibits both excellent heat resistance and high strength at high temperatures in addition to exceptional thermal shock resistance [1,2]. Silicon carbide exhibits high hardness at room temperature and excellent wear resistance. SiCf /SiC composites are expected to resist high-temperature creep and fatigue
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