Thermal Barrier Coating Adhesion via Mixed Oxide Layer
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Solution Overview
Problem
Gadolinia zirconia thermal barrier coatings exhibit lower spallation resistance compared to zirconia coatings, limiting their application despite having lower thermal conductivity, and adding a 7YSZ layer between the GdZr coating and substrate increases weight and processing costs.
Innovation Solution
A thermally grown mixed oxide layer is formed between the metallic substrate and the thermal barrier coating, enhancing spallation resistance, using a composition of about 51 weight percent gadolinia and 49 weight percent yttria partially stabilized zirconia, which improves adhesion and reduces spallation during thermal cycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If gadolinia zirconia thermal barrier coating is used, then thermal conductivity is reduced, but spallation resistance deteriorates
Solution Approach 1:
A thermally grown mixed oxide layer is introduced as an intermediary between the gadolinia zirconia thermal barrier coating and the metallic substrate. This intermediate layer improves interfacial compliance and stress distribution, thereby enhancing spallation resistance while preserving the low thermal conductivity of the gadolinia zirconia coating.
Solution Approach 2:
The coating system is structured as a composite consisting of multiple layers: the gadolinia zirconia thermal barrier coating, the thermally grown mixed oxide intermediate layer, and the metallic substrate. This composite structure combines the thermal insulation properties of gadolinia zirconia with the improved adhesion and stress tolerance provided by the mixed oxide layer.
2Reliability
If a 7YSZ layer is added between GdZr coating and substrate, then spallation resistance is improved, but weight and processing cost increase
Solution Approach 1:
The thermally grown mixed oxide layer is formed in situ on the metallic substrate through controlled thermal exposure before applying the gadolinia zirconia coating. This self-forming intermediate layer eliminates the need for adding a separate 7YSZ layer, thereby maintaining coating weight minimization while achieving improved spallation resistance.
3Reliability
If a 7YSZ layer is added between GdZr coating and substrate, then spallation resistance is improved, but processing complexity increases
Solution Approach 1:
The thermally grown mixed oxide layer forms automatically during the preheating stage before coating deposition, utilizing the thermal exposure already required for the coating process. This self-forming mechanism integrates the creation of the intermediate layer into the existing processing sequence, avoiding the need for additional processing steps.
Solution Approach 2:
The thermally grown mixed oxide layer is formed in advance during the preheating stage before the gadolinia zirconia coating is applied. This preliminary formation of the intermediate layer ensures optimal adhesion and stress distribution properties are established before the main coating process, simplifying the overall sequence.
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 increases the spallation resistance of gadolinia zirconia thermal barrier coatings while maintaining thermal protection, reducing the need for additional processing steps and weight, and enhancing interfacial compliance to mitigate stress configurations.
Implementation Method 1
a thermally grown mixed oxide layer between the metal substrate and the thermal barrier coating enhances the spallation resistance of the coating
Implementation Method 2
external surfaces that are insulated with ceramic thermal barrier coatings
Data Source
AI summary
A method of forming a spallation resistant thermal barrier coating on a metal substrate includes cleaning the substrate and preheating the substrate to a temperature suitable for the deposition of a thermal barrier coating according to a preheating schedule that allows a thermally grown mixed oxide layer to form on the substrate. A ceramic thermal barrier coating deposited on the thermally grown mixed oxide layer forms a spallation resistant coating.