Diffusion Aluminide Coating for Turbine Internal Cavities
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Solution Overview
Problem
Conventional aluminide coating processes struggle to uniformly coat internal surfaces of gas turbine components with complex geometries, often resulting in incomplete coverage, excessive thickness, and the formation of residual 'bisque' that obstructs air flow and requires costly scrapage.
Innovation Solution
A method involving dedicated elongated members coated with aluminum-based slurries, positioned within internal cavities without contact, and heated to vaporize aluminum, which diffuses onto internal surfaces, forming a uniform aluminide coating while using an inert gas to remove activator and binder precursors, preventing bisque formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional direct application of donor and activator to internal surfaces is used, then coating coverage is achieved, but excessive thickness and residual bisque formation occur
Solution Approach 1:
An elongated member coated with aluminum-based slurry serves as an intermediary carrier, positioned within the internal cavity without direct contact to internal surfaces. This mediator enables controlled aluminum vapor generation and diffusion onto the internal surfaces, preventing direct application issues that cause excessive thickness and bisque formation.
Solution Approach 2:
The mechanical direct application system is replaced with a thermal-vapor diffusion system. Aluminum is applied as a slurry coating on the elongated member, then heated to vaporize the aluminum, which diffuses onto the internal surfaces. This substitution eliminates the mechanical contact and direct deposition problems.
2Manufacturing precision
If internal surfaces with complex geometries are coated directly, then complete coverage is attempted, but uneven thickness and obstruction of cooling passages occur
Solution Approach 1:
The elongated member acts as a remote intermediary source positioned within the cavity, allowing aluminum vapor to diffuse uniformly onto complex internal surfaces without direct contact. This approach accommodates complicated geometries and cooling passages, preventing obstruction while achieving complete coverage.
Solution Approach 2:
The coating process transitions from direct material application to vapor-phase diffusion by changing the physical state parameter of aluminum from solid/slurry to vapor. This parameter change enables uniform deposition on complex geometries and ensures cooling passages remain unobstructed.
3Productivity
If aluminum-based slurry is directly applied to internal surfaces, then coating is achieved, but bisque requires costly scrapage and material waste occurs
Solution Approach 1:
Direct mechanical application of slurry is replaced with thermal vaporization and diffusion. The aluminum slurry on the elongated member is heated to vaporize the aluminum, which then diffuses onto internal surfaces. This substitution eliminates bisque formation and the associated scrapage requirements, improving productivity and reducing material waste.
Solution Approach 2:
The process utilizes phase transition of aluminum from solid/slurry state to vapor state through heating, then condensation and diffusion onto the substrate. This phase transition mechanism enables clean coating deposition without bisque formation, eliminating the need for scrapage operations.
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
This approach ensures uniform, thin, and high-quality aluminide coatings with reduced surface oxides and bisque, improving corrosion, oxidation resistance, and thermal shock resistance, while simplifying the coating process and reducing material waste.
Implementation Method 1
heating to melt and diffuse the powder into the surface
Implementation Method 2
The vaporized aluminum transfers to the metallic substrate surface and diffuses into the metal surface
Implementation Method 3
The aluminum reacts with the substrate to form intermetallic compounds
Implementation Method 4
Aluminide coatings are based on intermetallic compounds formed when nickel and cobalt react with aluminum at the substrate's surface
Implementation Method 5
heating a metallic substrate surface in the presence of an aluminum containing source material
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3F
AI summary
Unique and improved methods and coating apparatuses for applying diffusion aluminide materials onto internal sections of various parts are disclosed. The source material is coated onto an elongated member, such as a wire or rod, which is subsequently inserted at a specific location into a hollow cavity of the component to be coated. Improvements in the coating process and resultant coating include the ability to coat complex geometries and coat components with uniform thicknesses that do not require post-coating steps for removal of oxides and/or residual bisque.