Abrasive Blade Tip Coating with Ductile Interlayer for Fatigue Resistance
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Solution Overview
Problem
Cobalt contamination in nickel strike layers of turbine engine compressor blade tip coatings leads to property alterations and fatigue issues due to crack propagation from the abrasive layer into the blade substrate, necessitating an improvement in fatigue performance.
Innovation Solution
Incorporating a cobalt alloy interlayer between the strike layer and the abrasive coating, which is tougher or more ductile than the strike layer and the matrix, to prevent crack propagation and enhance fracture toughness, thereby improving the fatigue performance of the blade.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nickel strike layer is applied to the substrate, then adhesion is improved, but cobalt contamination occurs leading to property alterations and fatigue issues
Solution Approach 1:
A nickel-cobalt alloy interlayer is introduced between the nickel strike layer and the abrasive coating. This interlayer acts as a mediator that contains the cobalt contamination within a controlled zone, preventing it from reaching the substrate while maintaining adhesion. The interlayer has a gradient composition with higher cobalt content near the strike layer and lower cobalt content toward the abrasive coating, effectively isolating the substrate from harmful cobalt effects.
Solution Approach 2:
The coating system is segmented into multiple distinct layers: the nickel strike layer, the nickel-cobalt alloy interlayer, and the nickel matrix with abrasive coating. This segmentation isolates the cobalt contamination to a specific zone (the interlayer) rather than allowing it to affect the entire coating system or reach the substrate, thereby resolving the contradiction between maintaining adhesion and preventing fatigue degradation.
2Reliability
If the strike layer is made thinner to reduce cobalt contamination, then fatigue performance improves, but adhesion may be compromised
Solution Approach 1:
The nickel-cobalt alloy interlayer serves as an intermediary that compensates for the reduced thickness of the strike layer. It provides an additional bonding interface between the strike layer and the abrasive coating, ensuring that adhesion is maintained even when the strike layer is made thinner to reduce cobalt contamination and improve fatigue performance.
3Strength
If cobalt is added to the nickel strike layer to improve ductility, then toughness increases, but crack propagation occurs into the substrate
Solution Approach 1:
The cobalt content is distributed non-uniformly within the nickel-cobalt alloy interlayer, creating a gradient composition. The interlayer has higher cobalt content near the strike layer (providing toughness) and lower cobalt content toward the abrasive coating (reducing crack propagation risk). This local variation in composition allows the system to benefit from cobalt-induced toughness while preventing crack propagation into the substrate.
Solution Approach 2:
The nickel-cobalt alloy interlayer acts as a mediator that contains cobalt in a controlled gradient structure, allowing the strike layer to benefit from cobalt's toughening effect while preventing cobalt-rich regions that would promote crack propagation. The interlayer's gradient composition creates a transition zone that manages both toughness and crack resistance.
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 interlayer effectively arrests cracks at the abrasive-matrix interface, preventing propagation into the substrate and reducing the risk of coating failure, thereby enhancing the durability and reliability of the blade.
Implementation Method 1
a bond layer formed as an electrolytic nickel strike (via Wood's nickel solution) atop the substrate
Implementation Method 2
abrasive grit is tacked to the strike layer utilizing a sulfamate nickel plating chemistry
Implementation Method 3
the remainder of the nickel matrix is applied to complete the coating utilizing a sulfamate nickel plating chemistry
Implementation Method 4
The completed coating is baked in an air, argon, or vacuum atmosphere (e.g., at 375° F. to 1000° F. (190° C. to 538° C.)) to stress relieve the plated deposited and to abate hydrogen embrittlement
Data Source
AI summary
A blade has an airfoil having a tip. The blade has a metallic substrate and a coating system atop the substrate at the tip. The coating system has: a first layer of at least 99.0% weight nickel; an abrasive layer having a matrix and an abrasive at least partially embedded in the matrix; and a second layer between the first layer and the matrix. The second layer is tougher or more ductile than at least one of the first layer and the matrix.