Nanostructured Piston Seal Coating for High-Temperature Wear
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Solution Overview
Problem
Piston rings in gas turbine engines experience significant wear and increased friction due to chromia and alumina formation at high temperatures, leading to creep and wear issues in mid-turbine-frame seal locations despite using nickel-based superalloys for improved creep resistance.
Innovation Solution
A nanostructured, self-lubricating coating material comprising a binder matrix, hardener, and solid lubricants is applied to the seal-counterface, specifically using nickel-based compositions like NiCr, Ni-Co, or NiMoAl with glass, chrome carbide, silver, and calcium fluoride, providing a thickness of 4 to 10 mils to reduce friction and enhance wear resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nickel-based superalloys are used for piston seals to improve creep resistance, then creep resistance is improved, but wear resistance deteriorates due to chromia and alumina formation increasing friction
Solution Approach 1:
The invention applies a composite coating system consisting of multiple layers: a bond coat, an intermediate coat containing chromia-forming alloy, and an outer protective coat. This composite structure combines materials with different properties to achieve both creep resistance from the nickel-based superalloy substrate and wear resistance from the protective coating layers, resolving the contradiction between improved creep resistance and deteriorated wear resistance
Solution Approach 2:
The invention changes the surface chemistry parameters of the piston seal by applying coatings with specific compositional gradients. The intermediate coat contains chromia-forming alloy at controlled concentrations, and the outer coat provides a protective surface layer, thereby modifying the friction and wear characteristics without altering the bulk creep-resistant properties of the nickel-based superalloy
2Temperature
If chromia and alumina form on the piston ring surface at high temperatures, then high temperature operation is enabled, but friction increases leading to additional wear
Solution Approach 1:
The invention converts the harmful effect of chromia formation into a beneficial protective mechanism. The intermediate coat is specifically designed to form a controlled chromia layer that acts as a protective barrier, reducing direct metal-to-metal contact and lowering friction. This transforms the previously harmful oxidization into a protective function that reduces wear while maintaining high temperature operation
Solution Approach 2:
The multi-layer coating system combines materials with different functional properties: the bond coat provides adhesion, the intermediate chromia-forming coat provides oxidation protection and friction reduction, and the outer protective coat provides mechanical protection. This composite structure enables high temperature operation while minimizing friction and wear
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 coating significantly reduces wear and friction, enhancing the endurance life of engine components and reducing overhaul costs by minimizing counterface part replacement due to thermal and vibratory stress.
Implementation Method 1
a coating on the seal at the seal-counterface, wherein the coating comprises a nanostructured, self-lubricating coating material
Data Source
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AI summary
A piston seal assembly (10) for a gas turbine engine includes a seal (20) formed of a nickel-based superalloy; a component in contact with the seal (20) and defining a seal-counterface (18); and a coating (22) on the seal (20) at the seal-counterface (18), wherein the coating (22) is a nanostructured, self-lubricating coating material.