Abradable Coating Deposition on CMC Shrouds

The patent replaces the plasma spray mechanical deposition system with a chemical solution-based dip coating system. The slurry containing ceramic particulates and sol-gel precursors is immersed onto the CMC shroud, allowing complete material utilization without the waste inherent in spray processes. The chemical bonding mechanism through sol-gel transformation ensures reliable coating adhesion without requiring high-energy plasma fields.

The patent changes the deposition parameters from high-energy plasma spray to low-energy dip coating followed by controlled thermal processing. The slurry is applied at room or elevated temperatures, then dried and sintered in a controlled atmosphere furnace. This parameter change transforms the deposition mechanism from mechanical impact to chemical precipitation and thermal consolidation, improving material efficiency.

The patent applies preliminary patterning to the CMC shroud surface before coating deposition. Ridges or grooves are pre-formed on the shroud, and the slurry is then dip-coated over these features. The metal mask is eliminated because the substrate geometry itself provides the pattern template, preventing material waste from mask coverage areas while still creating the desired ridge structure for blade rub protection.

The patent extracts and eliminates the metal mask component from the coating process. Instead of using a mask to define the ridge pattern, the shroud surface is pre-formed with the desired geometry, and the coating slurry conformally deposits over these features. This removes the material waste associated with masking areas that receive no coating.

The patent creates a composite structure by depositing a ceramic-based abradable coating onto the CMC shroud. The coating comprises ceramic particulates (such as alumina, silica, or rare earth oxides) bound with a glassy matrix formed from sol-gel precursors. This composite coating is softer than the CMC substrate, providing a sacrificial layer that protects the harder CMC shroud from damaging blade contact while maintaining the shroud's high-temperature capability.

The patent creates a porous abradable coating structure through controlled sintering of the sol-gel derived ceramic material. The porous structure, with controlled porosity and interconnected voids, allows the coating to be more compliant and easier to abrade compared to dense CMC material. When blade contact occurs, the porous structure collapses and erodes preferentially, protecting the underlying CMC shroud from damage.

The patent replaces mechanical plasma spray deposition with chemical sol-gel based dip coating. The slurry is immersed onto the CMC shroud and then undergoes controlled drying and sintering. The chemical bonding mechanisms through sol-gel transformation and sintering create strong adhesion to the CMC substrate, preventing coating loss that plagues mechanically applied coatings while maintaining manufacturing simplicity.

The patent utilizes phase transitions in the sol-gel process to ensure durable coating formation. The organic precursors in the slurry undergo hydrolysis and condensation to form an inorganic gel network, which then dries to a xerogel state, and finally sinters to a dense ceramic structure. These controlled phase transitions create strong chemical bonds between the coating and CMC substrate, preventing coating delamination and loss during service.