Coated CBN Welding for Oxidation-Resistant Blade Tip Sealing
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Solution Overview
Problem
Existing methods for applying cubic boron nitride (CBN) in gas turbines face challenges such as poor bonding with other materials, high cost, complexity, and lack of corrosion resistance, leading to oxidation and layer thickness limitations.
Innovation Solution
A corrosion-resistant matrix material MCrAlY is applied using laser buildup welding, combined with a protective envelope of titanium carbide (TiC) to coat CBN particles, allowing for better bonding and controlled layer thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CBN particles are applied to protect blade tips during rubbing-in, then the blade tip protection is improved, but the bonding between CBN and other materials deteriorates
Solution Approach 1:
The patent applies a multi-layer composite coating system on CBN particles consisting of an inner TiC layer for bonding and an outer Al2O3 layer for oxidation resistance. This composite structure resolves the contradiction by combining materials with complementary properties: TiC provides strong metallurgical bonding to the substrate while Al2O3 protects the CBN from oxidation during high-temperature operation.
Solution Approach 2:
The TiC coating layer acts as an intermediary between the CBN particle and the metal substrate. It facilitates strong bonding between the ceramic CBN and the metallic blade tip material, solving the inherent bonding difficulty between dissimilar materials while allowing the CBN to function as a protective abrasive layer.
2Ease of manufacture
If electrochemical application or inductive soldering-on is used to apply CBN, then the CBN application is achieved, but the process cost and complexity increase
Solution Approach 1:
The CBN particles are pre-coated with the multi-layer system (TiC inner layer and Al2O3 outer layer) before application to the blade tips. This preliminary preparation ensures that the particles have the necessary bonding and oxidation-resistant properties built-in, eliminating the need for complex post-application processing or specialized application equipment.
Solution Approach 2:
The patent replaces complex electrochemical or inductive soldering processes with a simpler thermal spray or plasma spray application method. The pre-coated CBN particles can be applied using conventional thermal processes that are less complex and more cost-effective while achieving the same bonding and protection results.
3Ease of manufacture
If resin derivatives are used as embedding material for CBN, then the CBN application is simplified, but the temperature resistance deteriorates
Solution Approach 1:
The patent replaces organic resin embedding materials with an inorganic ceramic-based embedding matrix (such as metal matrix or ceramic matrix). This composite approach maintains the simplicity of embedding while achieving the high-temperature resistance required for turbine blade applications, as inorganic materials can withstand the thermal environment without degrading.
4Ease of manufacture
If conventional coating materials are used for CBN particles, then the application is simplified, but the hot gas corrosion resistance deteriorates
Solution Approach 1:
The patent uses a composite coating system with TiC as the inner layer and Al2O3 as the outer layer. The Al2O3 outer layer provides excellent resistance to hot gas corrosion and oxidation, while the TiC inner layer ensures strong bonding to the CBN particle. This composite structure achieves superior corrosion resistance while maintaining manufacturing feasibility.
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 method enhances the durability and bonding of CBN particles, providing improved hot gas corrosion resistance and enabling layer thickness control, ensuring the protective function lasts for many hours of operation.
Implementation Method 1
MCrAlY is applied by means of laser buildup welding
Implementation Method 2
laser buildup welding
Implementation Method 3
Only when hot-gas-resistant carbide coatings, in particular Tic, are used does cBN survive the residence time in the laser beam without damage
Data Source
AI summary
A welding method using coated abrasive particles, coated abrasive particles, coating system and sealing system which uses particles, in which a hard material layer is applied around abrasive particles such as cubic boron nitride (cBN) and protects against oxidation during welding. The hard material compound in the coating may include a carbide, in particular titanium carbide. A sealing system is composed of stator and rotor blade having the layer system.