Self-Braze Abrasive Coating for Gas Turbine Clearance Control
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Solution Overview
Problem
Existing methods for applying abrasive coatings to gas turbine engine components, such as blade tips, often result in inadequate clearance between rotating parts, leading to inefficiencies due to insufficient wear-in of abradable coatings by abrasive materials.
Innovation Solution
A method involving a self-braze material comprising a sintered sheet of low and high melting point alloys, with cubic boron nitride abrasive embedded in an MCrAlY matrix, applied to a substrate through slurry plating and subsequent brazing, ensuring effective bonding and wear-in for optimal clearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If direct plating or direct spraying methods are used to apply abrasive to blade tips, then the application process is simplified, but the wear-in performance and clearance control are insufficient
Solution Approach 1:
The abrasive particles are pre-embedded in a matrix material before application to the blade tip. This preliminary configuration ensures proper abrasive orientation and distribution, enabling both ease of application and precise wear-in control during engine operation.
Solution Approach 2:
A composite coating structure is used consisting of a matrix material (such as MCrAlY) with abrasive particles embedded within it. This composite approach combines the benefits of easy application of the coating material with the precision wear-in characteristics of the embedded abrasive, resolving the contradiction between manufacturing ease and precision control.
2Strength
If pre-formed abrasive is brazed to the substrate, then the bonding strength is improved, but the process complexity increases
Solution Approach 1:
The abrasive embedding, matrix application, and bonding operations are merged into a single integrated coating process. The abrasive-containing coating material is applied and bonded in one step, eliminating the need for separate pre-forming and brazing operations, thus maintaining strong bonding while reducing process complexity.
Solution Approach 2:
The matrix material serves as an intermediary between the abrasive particles and the substrate. It facilitates bonding while holding the abrasive particles in position, enabling strong attachment without requiring complex multi-step processes for separate abrasive fixation and matrix application.
3Productivity
If higher abrasive content is used in the coating, then the wear-in capability is enhanced, but the coating durability and adhesion deteriorate
Solution Approach 1:
The chemical composition parameters of the matrix material are optimized to achieve the right balance. By adjusting elements such as chromium, aluminum, and nickel content, the coating achieves both high abrasive content for effective wear-in and sufficient adhesion strength for long-term durability under thermal and mechanical stress.
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 solution achieves a precise and durable wear-in of abrasive coatings, reducing gas blow-by and enhancing the efficiency and longevity of gas turbine engine components by maintaining low radial clearance between blade tips and stationary structures.
Implementation Method 1
a self-braze material wherein the self-braze material comprises a sintered sheet of: at least one first alloy of low melting point relative to the substrate and at least one second alloy of high melting point relative to the first alloy
Implementation Method 2
heating to cause the self-braze material to braze to the substrate
Implementation Method 3
at least one first alloy of low melting point relative to the substrate
Implementation Method 4
The abrasive functions to abrade the abradable coating and provide a wear-in to a low radial clearance value between blade and BOAS
Data Source
Figure 1
AI summary
A method for applying an abrasive (42) comprises: applying, to a substrate (24), the integral combination (20) of: a self-braze material (30); an abrasive (42); and a matrix (44) in which the abrasive is at least partially embedded; and heating to cause the self-braze material to braze to the substrate. The heating leaves at least a portion of the self-braze material with a composition comprising, in weight percent: cobalt 2.5-13.5; chromium 12-27; aluminum 5-7; yttrium 0.0-1.0; hafnium 0.0-1.0; silicon 1.0-3.0; tantalum 0.0-4.5; tungsten 0.0-6.5; rhenium 0.0-2.0; molybdenum 0.1-1.0; and the balance nickel.