Chromia Layer Formation on Low Chromium Nickel Alloy
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Solution Overview
Problem
Low chromium content nickel-based alloys are prone to undesirable formation of a nickel oxide scale, which is undesirable in certain applications where oxidation resistance is needed.
Innovation Solution
A method for forming a dense layer of chromia on a low chromium content nickel-based alloy substrate by applying a chromia promoter mixture and performing a heat treatment, allowing oxygen to diffuse and react with chromium to form a continuous, high-density chromia layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If chromium concentration in nickel-based alloy is reduced below 30 wt.%, then other alloying elements can be increased, but nickel oxide scale formation is promoted
Solution Approach 1:
A chromia promoter coating is applied to the substrate surface before service, and a heat treatment is performed in advance to form a dense chromia layer. This preliminary protective layer prevents nickel oxide scale formation during subsequent high-temperature exposure, allowing the use of low chromium content alloys without suffering from oxidation problems.
Solution Approach 2:
The invention changes the chemical composition parameters of the surface coating by incorporating chromia promoters (such as chromium oxide, chromium nitride, or chromium carbide) in specific concentrations. The heat treatment parameters (temperature, time, atmosphere) are also optimized to control the formation of dense chromia layer with specific crystal structure and morphology, thereby achieving oxidation resistance.
2Stability of the object's composition
If chromium concentration is increased to 30 wt.% or more, then alloy stability is improved, but the concentration of other elements must be decreased
Solution Approach 1:
The invention creates a non-uniform chromium distribution where the substrate maintains low chromium content (1-30 wt.%) for cost-effectiveness and flexibility in adding other alloying elements, while the surface coating is enriched with chromia promoters to provide localized oxidation protection. This spatial separation allows the bulk alloy to have optimized composition for mechanical properties while the surface provides corrosion resistance.
3Object-affected harmful factors
If a dense chromia layer is formed on low chromium content alloy, then oxidation resistance is achieved, but additional processing steps are required
Solution Approach 1:
The invention creates a composite structure consisting of a low chromium nickel-based alloy substrate combined with a chromia promoter coating layer. This composite material system leverages the advantages of both components: the substrate provides mechanical strength and cost-effectiveness, while the coating layer provides oxidation resistance. The composite structure is formed through conventional coating techniques followed by heat treatment, which are standard industrial processes.
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 effectively reduces the likelihood of nickel oxide scale formation, providing excellent oxidation resistance to the substrate while maintaining a low chromium content alloy.
Implementation Method 1
during the heat treatment oxygen diffuses from the at least one chromia promotor and reacts with the chromium in the substrate to form the layer of chromia on the surface
Implementation Method 2
oxygen diffuses from the at least one chromia promotor and reacts with the chromium in the substrate to form the layer of chromia on the surface
Implementation Method 3
forming a layer of chromia (Cr 2 O 3) on the surface of the substrate by performing a heat treatment on the surface with the mixture thereon
Data Source
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AI summary
Components and methods for forming a layer of chromia on a substrate thereof are provided. The methods include forming a mixture that includes at least one chromia promoter, applying the mixture to a surface of a substrate formed of a nickel-based alloy having between 1 wt.% and 30 wt.% chromium, and forming a layer of chromia (Cr2O3) on the surface of the substrate by performing a heat treatment on the surface with the mixture thereon, wherein during the heat treatment oxygen diffuses from the at least one chromia promotor and reacts with the chromium in the substrate to form the layer of chromia on the surface.