Graded CTE Abradable Coating for CMC Shroud Spallation

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Solution Overview

Problem

Current abradable coatings for CMC shrouds in gas turbine engines face challenges such as aerodynamic losses, difficulty in producing thick continuous layers without spallation, and the risk of damaging rotating blades due to their hardness, while also being susceptible to high temperature steam recession.

Innovation Solution

A coating system comprising an environmental barrier coating with an abradable coating having the formula Ln2ABO8, where Ln includes rare earth elements and A and B comprise Si, Ti, Ge, Mo, or W, providing a graded coefficient of thermal expansion from the interface with the environmental barrier coating to the external surface, which is thick, dense, and mechanically resistant to spall and rub, serving as a sacrificial layer to protect the underlying EBC.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a thick continuous layer of EBC material is produced, then protection against steam recession is improved, but spallation occurs

Engineering Contradiction:

Improveprotection against steam recessionVSAvoidspallation

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent applies composite materials by combining EBC layer with abradable coating layer having different properties. The EBC layer provides steam recession protection while the abradable coating layer provides rub protection and prevents spallation. This composite structure allows achieving both thick continuous coverage and resistance to spallation simultaneously.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent applies local quality by creating different functional layers with different properties. The EBC layer is optimized for steam protection while the abradable coating layer is optimized for mechanical rub protection. Each layer has specific local properties suited to its function, allowing the system to achieve both steam protection and spallation resistance.

Inventive Principle:

Principle #3Local quality

2Stability of the object's composition

If a continuous ceramic layer is deposited, then coating continuity is improved, but the layer becomes hard and damages rotating blades

Engineering Contradiction:

Improvecoating continuityVSAvoidblade damage

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent applies parameter changes by modifying the mechanical properties of the coating system. The abradable coating layer has controlled hardness and abrasion resistance parameters that allow it to sacrificially wear during blade rub events, protecting the harder EBC layer and the blade from damage. This parameter optimization enables the coating to be continuous and protective without being excessively hard.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If an abradable layer with ceramic ridges is deposited, then protection from blade rub is improved, but aerodynamic losses increase

Engineering Contradiction:

Improveprotection from blade rubVSAvoidaerodynamic losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent applies parameter changes by optimizing the surface morphology and material properties of the abradable coating. Instead of using traditional ceramic ridges that create significant aerodynamic losses, the patent uses a fine-grained or porous abradable coating that provides blade rub protection while minimizing surface protrusions that would cause aerodynamic losses. This parameter optimization enables the coating to be protective without significantly impacting aerodynamic performance.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The coating system effectively reduces the risk of coating loss, maintains engine efficiency by minimizing aerodynamic losses, and provides protection against high temperature steam recession while being resistant to spallation and rub events, thus enhancing the durability and performance of CMC shrouds.

Implementation Method 1

The abradable coating has a first coefficient of thermal expansion at an interface with the environmental barrier coating that changes to a second coefficient of thermal expansion at its external surface

Methodology Applied

Scientific EffectGraded coefficient of thermal expansion: Thermal Expansion

Data Source

PatentUS10145252B2Abradable compositions and methods for CMC shrouds

Publication Date: 2018.12.04 GENERAL ELECTRIC CO

AI summary

Coating systems on a surface of a CMC component, such as a CMC shroud, are provided. The coating system can include an environmental barrier coating on the surface of the CMC component and an abradable coating on the environmental barrier coating and defining an external surface opposite of the environmental barrier coating. The abradable coating includes a compound having the formula: Ln2ABO8, where Ln comprises scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, or mixtures thereof; A comprises Si, Ti, Ge, or a combination thereof; and B comprises Mo, W, or a combination thereof. In one embodiment, the abradable coating has a first coefficient of thermal expansion at an interface with the environmental barrier coating that changes to a second coefficient of thermal expansion at its external surface. Methods are also provided for applying an abradable coating onto a CMC component.