Superalloy Coating Traps Sulphur to Prevent Oxide Flaking
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Solution Overview
Problem
Conventional coatings for protecting metallic superalloy substrates in turbomachines from oxidation and hot corrosion are susceptible to reduced service life due to the presence of sulphur, which can disrupt the oxide layer and cause flaking or loss of mass during thermal cycles.
Innovation Solution
A multi-layer coating process involving a first layer of aluminium and a sulphur-capturing element like zirconium, followed by an isolating aluminium layer, and a surface layer of platinum, is used to trap sulphur and maintain the oxide layer integrity, with a concentration peak of the sulphur-capturing element at the interface between the additional and diffused layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional coatings are used to protect superalloy substrates from oxidation and hot corrosion, then the coating provides basic protection, but the service life is reduced due to sulphur presence causing flaking and mass loss
Solution Approach 1:
A boron-containing intermediate layer is introduced between the aluminium-based protective layer and the superalloy substrate. This intermediate layer acts as a mediator that captures sulphur atoms, preventing them from reaching and disrupting the protective oxide layer. The boron forms a sulphur barrier that maintains the integrity of the coating system during thermal cycling, thereby extending service life.
Solution Approach 2:
The coating system is designed as a composite structure consisting of multiple layers: an aluminium-based protective layer, a boron-containing intermediate layer with sulphur-capturing capability, and a superalloy substrate. This composite structure combines the oxidation resistance of aluminium with the sulphur-trapping ability of boron, creating a synergistic effect that simultaneously provides protection against both oxidation and sulphur-induced hot corrosion.
2Reliability
If a single-layer aluminium coating is deposited to provide oxidation protection, then the oxide layer forms effectively, but sulphur disrupts this layer causing flaking during thermal cycles
Solution Approach 1:
The coating is segmented into distinct functional layers: an outer aluminium-based layer that forms the protective oxide, and an inner boron-containing intermediate layer that captures sulphur. This segmentation allows each layer to perform its specific function independently - the aluminium maintains oxide layer integrity while the boron prevents sulphur contamination, together enhancing overall coating stability during thermal cycling.
3Ease of manufacture
If the coating structure is simplified to reduce manufacturing complexity, then production is easier, but the ability to control sulphur distribution and protect against hot corrosion is reduced
Solution Approach 1:
The boron-containing intermediate layer is applied in advance during the coating deposition process, before the aluminium protective layer is formed. This preliminary action ensures that the sulphur-capturing layer is already in place to trap sulphur atoms as they diffuse through the coating, providing proactive protection against hot corrosion without requiring complex post-processing steps.
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 process effectively prevents sulphur-induced damage, enhancing the coating's resistance to oxidation and corrosion, thereby extending the service life of the thermal barrier by maintaining the integrity of the oxide layer and ensuring good oxidation and corrosion properties.
Implementation Method 1
a first layer of aluminium and of at least one element capable of being alloyed with sulphur
Implementation Method 2
A known coating is formed from an aluminium-based layer, which is generally deposited via a vapour phase aluminization process and attaches to the substrate by metallic interdiffusion and forms a protective surface oxide layer
Implementation Method 3
attaches to the substrate by metallic interdiffusion
Data Source
AI summary
To protect a superalloy substrate from oxidation and hot corrosion, disclosed herein is coating made by a process that deposits successive layers on the substrate, a first layer of aluminium and of at least one element capable of being alloyed with sulphur, and a second layer of a material that isolates the at least one element capable of being alloyed with sulphur.