Superalloy Thermal Barrier Coating Rumpling Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The 'rumpling' phenomenon, which involves deformation and delamination of thermal barrier coatings in turbomachines due to temperature variations, leads to premature damage and reduced lifespan of turbine blades, as existing solutions fail to completely prevent or delay this degradation mechanism effectively.
Innovation Solution
A manufacturing method that rectifies the surface state of the metal sub-layer through physico-chemical and/or mechanical processes to limit defects and ensure a controlled roughness, allowing for improved adhesion and stability of the ceramic layer, thereby inhibiting the 'rumpling' phenomenon and extending the thermal barrier's service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thermal barrier coating is deposited on a superalloy substrate to protect against high temperatures, then the resistance to high temperatures is improved, but the coating undergoes rumpling deformation and delamination due to thermal expansion differences
Solution Approach 1:
The coating is divided into multiple functional layers: a metallic substrate, an intermediate metallic sub-layer (MCrAlY or nickel aluminide), and a ceramic top layer (yttria-stabilized zirconia). This segmentation allows each layer to perform its specific function while managing thermal expansion differences through the gradient structure.
Solution Approach 2:
A metallic sub-layer is introduced as an intermediary between the superalloy substrate and the ceramic coating. This intermediate layer has a coefficient of thermal expansion that bridges the gap between the substrate and coating, preventing direct stress concentration and delamination at the interface.
2Loss of energy
If the ceramic layer is deposited directly on the substrate to maximize insulation, then the thermal conductivity is reduced, but the adhesion between layers is insufficient leading to delamination
Solution Approach 1:
The metallic sub-layer acts as a mediator that provides both mechanical anchoring and chemical bonding capabilities. It forms strong metallurgical bonds with the substrate while providing a suitable surface for ceramic deposition, ensuring adequate adhesion without compromising insulation thickness.
Solution Approach 2:
The thermal barrier system uses a composite structure combining metallic and ceramic materials with complementary properties. The metallic sub-layer provides ductility and adhesion, while the ceramic layer provides thermal insulation, creating a composite system that leverages the advantages of both material classes.
3Loss of energy
If the coating thickness is increased to improve insulation, then the thermal gradient amplitude is increased, but the stress from thermal cycling accelerates rumpling and reduces coating lifespan
Solution Approach 1:
The thick coating is segmented into multiple thinner layers (metallic sub-layer + ceramic layer), which distributes the thermal stress more evenly throughout the structure. This layered approach maintains insulation effectiveness while reducing the concentration of stresses that would otherwise lead to rapid failure.
Solution Approach 2:
The system changes the physical parameters of the coating structure by introducing an intermediate layer with intermediate thermal and mechanical properties. This gradient in properties allows the system to accommodate thicker total coating thickness while managing thermal stresses through the parameter transition across layers.
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 method significantly increases the spalling life of thermal barrier systems by preventing or delaying the 'rumpling' phenomenon, ensuring durable protection against high temperatures and maintaining the integrity of the ceramic layer, with easy and reproducible implementation.
Implementation Method 1
the adhesion between the undercoat and the substrate of the part is done by inter-diffusion, and that the adhesion between the undercoat and the ceramic layer is achieved by mechanical anchoring and by the propensity of the undercoat to develop at high temperature, at the ceramic/undercoat interface, a thin oxide layer which ensures the chemical contact with the ceramic
Implementation Method 2
electron beam evaporation deposition (EB-PVD) of a ceramic coating
Implementation Method 3
this insulating coating makes it possible to create on a cooled part, in steady state of operation, a thermal gradient through the coating, the total amplitude of which can exceed 100°C for a coating of approximately 150 to 200 μm in thickness
Implementation Method 4
the deposition of a thermal insulating coating called a thermal barrier composed of several layers, on the superalloy substrate
Data Source
Figure 1~3
Figure 4A~4B
Figure 4C~5C
AI summary
The invention relates to a method for producing a heat barrier covering a metal substrate made of a superalloy, said heat barrier including at least one sublayer and one ceramic layer, characterised in that the method comprises the following steps: rectifying the surface state of the sublayer using at least one physico-chemical and/or mechanical method before the deposition of the ceramic layer so that the number of defects having a space between the ridges lower than or equal to 2 µm does not exceed 5 over any 50 µm distance; and carrying out the deposition of the ceramic layer. The invention can be used for turbine blades.