Two-Layer Abrasive Blade Tip Coating for Turbine Wear Control
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Solution Overview
Problem
Rotor blade tips in turbines experience rapid abrasive wear and oxidation due to the lack of effective wear-resistant coatings, leading to premature coating removal and increased gap between blades and housing, which existing coatings like MCrAlY and TBC fail to address effectively.
Innovation Solution
A two-layer abrasive tape system comprising a cubic boron nitride (cBN) layer embedded in a NiCoCrAlY matrix with a high-temperature solder layer is applied to the blade tips, allowing controlled grinding and improved oxidation protection, where the cBN particles protrude from the outer layer and the solder layer is thin to minimize material impairment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard MCrAlY and TBC coatings are applied to blade tips, then oxidation protection is provided, but the coatings wear away quickly due to abrasive stresses during turbine start-up
Solution Approach 1:
The coating system is segmented into three distinct layers: a MCrAlY bond coat, a TBC protective layer, and a new cBN abrasive-resistant top coat. This segmentation allows each layer to perform its specific function - the MCrAlY provides oxidation resistance and bonding, the TBC provides thermal protection, and the cBN layer provides abrasive wear resistance during start-up
Solution Approach 2:
The invention uses a composite material system combining metal alloys (MCrAlY, TBC) with cubic boron nitride (cBN) abrasive particles. The cBN particles are embedded in a matrix material to create a composite coating that resists both oxidation and abrasive wear, overcoming the limitations of conventional single-material coatings
2Reliability
If cBN tapes are soldered onto already coated blades, then abrasive wear resistance is improved, but the existing coatings are compromised during soldering
Solution Approach 1:
The MCrAlY bond coat and TBC protective layer are applied to the blade tips before the cBN abrasive-resistant top coat is soldered onto the blade. This preliminary application of the metal coating system ensures that the coatings are already in place and can be properly integrated with the cBN layer during the subsequent soldering process, preventing coating compromise
3Reliability
If NiCoCrAlY layer is applied over cBN tapes, then oxidation protection is provided, but the layer wears away quickly exposing underlying particles
Solution Approach 1:
The NiCoCrAlY layer is applied selectively over the cBN tapes in the tip area where abrasive wear occurs, rather than coating the entire blade. This localized application provides oxidation protection exactly where needed while allowing the cBN particles to remain exposed for abrasive resistance. The layer is designed to wear away controllably to expose fresh cBN particles
4Manufacturing precision
If TBC overspray is present on tips, then complete coating coverage is achieved, but adhesion to NiCoCrAlY becomes too strong making removal difficult
Solution Approach 1:
The TBC coating is applied with intentional overspray beyond the required coverage area on the blade tips. This excessive application ensures complete coverage of the tip area including the cBN tapes and NiCoCrAlY layer. The overspray creates a controlled adhesion scenario where the TBC can be easily removed from the tip area while maintaining coverage where needed
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 two-layer tape system significantly extends the service life of rotor blades by reducing wear and providing enhanced oxidation protection, achieving a 0.4% increase in efficiency through improved tip hardening and controlled grinding capabilities.
Implementation Method 1
an outermost second layer (10), in particular a layer of a metallic matrix material, in particular a NiCoCrAlY layer or a NiCoCrAlY layer containing abrasive particles, in particular cubic boron nitride (cBN), wherein the abrasive particles (19) are embedded in the outer layer (10), in particular in the NiCoCrAlY layer (10), wherein the two-layer tape (5, 10) can be sintered close to the contour and applied directly to the tips (13) of the rotor blades (4)
Implementation Method 2
designed to wear away effectively during turbine start-up. This design would allow for controlled blade grinding into an existing stator coating
Implementation Method 3
providing enhanced oxidation protection
Data Source
Figure 1~2
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.