Rotor Blade Tip Abrasive Coating for Controlled Bedding-In
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Solution Overview
Problem
Rotor blade tips in turbines experience rapid wear due to abrasive stresses, leading to coating failure and increased oxidation and corrosion, which results in an undesirable gap between blades and housing, and existing wear-resistant coatings are not effective.
Innovation Solution
A two-layer coating system comprising a close-to-contour application of cubic Boron Nitride (cBN) particles embedded in a metal matrix, specifically an NiCoCrAlY layer, with a high-temperature solder layer for bonding, applied before the standard NiCoCrAlY and TBC layers to prevent impairment during soldering and ensure controlled bedding-in.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard MCrAlY and TBC coating is applied to the blade tip, then the coating provides initial oxidation protection, but it is worn away quickly during the bedding process due to abrasive stresses
Solution Approach 1:
The patent applies a wear-resistant coating to the blade tip before the standard MCrAlY and TBC layers. This preliminary wear-resistant layer protects the subsequent layers during the abrasive bedding process, preventing them from being worn away quickly while still allowing controlled bedding-in to occur.
Solution Approach 2:
The patent creates a multi-layer composite coating structure consisting of a wear-resistant outer layer (containing ceramic particles like alumina or silica) combined with the standard MCrAlY and TBC layers. This composite structure provides both wear resistance during bedding and oxidation protection during operation, resolving the contradiction between coating durability and lifespan.
2Duration of action of moving object
If a wear-resistant coating is applied to the blade tip, then coating lifespan is extended, but the coating must allow controlled bedding-in to occur
Solution Approach 1:
The wear-resistant coating is applied locally to the blade tip region where abrasive stresses occur during bedding, while the rest of the blade maintains the standard coating structure. This localized application ensures wear protection exactly where needed while allowing controlled bedding-in behavior in the contact region.
Solution Approach 2:
The wear-resistant coating provides more protection than initially needed, but this excessive protection is acceptable because it only needs to last through the bedding process. After bedding is complete, the coating has fulfilled its purpose and can be replaced or worn away, allowing the underlying oxidation-resistant layers to perform their function long-term.
3Object-affected harmful factors
If the blade tip is protected against wear, then oxidation and corrosion damage is reduced, but manufacturing complexity increases due to multiple coating layers
Solution Approach 1:
The coating system is segmented into distinct functional layers: a wear-resistant outer layer containing ceramic particles, an intermediate MCrAlY layer providing oxidation resistance and bonding, and an outer TBC layer for thermal protection. Each layer performs a specific function, allowing the complex protection requirements to be divided into manageable, specialized components.
Solution Approach 2:
The multi-layer coating structure provides multiple functions simultaneously: wear resistance during bedding, oxidation protection during operation, thermal barrier protection, and controlled bedding-in behavior. By integrating these multiple functions into a single coating system, the patent reduces overall complexity compared to applying separate treatments for each function.
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 significantly increases the lifespan of rotor blades by minimizing wear and providing enhanced oxidation protection, allowing for controlled bedding-in and improved efficiency by 0.4%.
Implementation Method 1
an outermost second coating (10) as further layer there is a layer of a metallic matrix material, in particular an NiCoCrAlY alloy or an NiCoCrAlY alloy, which comprises abrasive particles, in particular particles of cubic boron nitride (cBN)
Implementation Method 2
the coatings can be impaired during soldering at temperatures above 1473K (diffusion of aluminum into the base material, coarsening of the β-phase, Kirkendal porosity, etc.)
Implementation Method 3
Rotor blade tips as illustrative component are subjected to extreme abrasive stresses during the bedding process
Implementation Method 4
particles of cBN (cubic Boron Nitride)... having embedded abrasive particles, in particular cBN particles
Implementation Method 5
the blades no longer being protected against oxidation or corrosion. The oxidation- and corrosion-related damage
Data Source
AI summary
An excellent abrasive blade tip is provided by a two-layer coating system consisting of a brazing solder coating and an NiCoCrAlY coating containing cBN (cubic Boron Nitride).