Chromizing Over Cathodic Arc Coating for Gas Turbine Blades
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Solution Overview
Problem
Conventional methods for producing Cr-rich coatings to enhance hot corrosion resistance in gas turbines are costly and result in significant loss of coating thickness due to aggressive processes like grit blast and spallation.
Innovation Solution
A method involving the application of a MCrAlY coating using cathodic arc deposition followed by a diffused chromide coating with greater than 50% chromium by weight, applied through pack chromizing, slurry chromizing, or vapor diffusion, eliminating the need for post-treatment processes like grit blast and heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a secondary coating is applied under high chromium cathodic arc coating to increase hot-corrosion resistance, then hot corrosion resistance is improved, but manufacturing cost increases and coating thickness is lost due to grit blast and spallation
Solution Approach 1:
The invention combines the hot corrosion resistance function and the Cr-rich layer formation into a single integrated coating process. The MCrAlY coating is applied first to provide base protection, then a diffused chromide coating is applied over it to create the Cr-rich surface layer. This merging eliminates the need for separate secondary coating applications and aggressive grit blast preparation steps, thereby reducing manufacturing cost while maintaining improved hot corrosion resistance.
Solution Approach 2:
The MCrAlY coating is applied in advance as a preparatory layer before applying the diffused chromide coating. This preliminary action provides a stable substrate that enhances the adhesion and performance of the final Cr-rich coating, eliminating the need for subsequent corrective treatments or additional coating layers that would increase cost and complexity.
2Reliability
If conventional combined coating process is used to improve hot corrosion resistance, then hot corrosion resistance is improved, but coating thickness is significantly lost due to aggressive grit blast and spallation
Solution Approach 1:
The invention extracts and eliminates the harmful grit blast and spallation steps from the conventional coating process. By using a diffused chromide coating applied over the MCrAlY coating, the process achieves the desired Cr-rich surface layer without the aggressive mechanical preparation that causes thickness loss, thereby preserving coating thickness while maintaining hot corrosion resistance improvement.
3Reliability
If MCrAlY coating is applied with cathodic arc deposition followed by diffused chromide coating, then hot corrosion resistance is improved without additional cost and thickness loss, but process complexity increases
Solution Approach 1:
The invention changes the chemical composition parameters of the coating layers by controlling the chromium content in the MCrAlY coating (25-50 wt%) and the diffused chromide coating (>50 wt% Cr). This parameter optimization allows the two-layer system to achieve superior hot corrosion resistance through controlled diffusion and reaction during processing, balancing performance improvement with manageable process complexity.
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 provides superior hot corrosion resistance without the costs and thickness losses associated with conventional methods, maintaining performance in low cycle fatigue and stress corrosion tests, and forming a protective Cr-rich oxide scale that prevents corrosive contaminants from depositing on gas turbine hardware.
Implementation Method 1
applying a MCrAlY coating on a substrate using cathodic arc deposition
Implementation Method 2
applying a diffused chromide coating atop the MCrAlY coating by pack chromizing, slurry chromizing, vapor diffusion coating, or gas diffusion coating
Implementation Method 3
applying a diffused chromide coating atop the MCrAlY coating by pack chromizing, slurry chromizing, vapor diffusion coating, or gas diffusion coating
Data Source
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AI summary
The present invention provides a Cr-rich cathodic arc coating, an article in turbine blade coated with the chromizing over cathodic arc coating, and a method to produce the coating thereof. The Cr-rich cathodic arc coating in the present invention comprises a cathodic arc coating and a diffusion coating deposited atop the cathodic arc coating to enforce hot corrosion resistance. The hardware coated with the chromizing over cathodic arc coating in the present invention is reinforced with superior- hot corrosion resistance. The present invention further provides a novel method for producing the chromizing over cathodic arc coating by re-sequencing coating deposition order. The method in the present invention is efficient and cost-reducing by eliminating some operations, e.g., DHT and peening, between the cathodic arc coating and the diffusion coating. The hot corrosion resistance in the present invention results from the high Cr content in the surface of the coating.