Nickel-Based Superalloy Composition for Single-Crystal Turbine Blades
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Solution Overview
Problem
Nickel-based superalloys used in gas turbines face issues with creep resistance, microstructural stability, and formation of undesirable phases at high temperatures, leading to reduced mechanical strength and increased production costs due to defects like freckle grains and secondary reaction zones.
Innovation Solution
A nickel-based superalloy composition with specific weight percentages of elements such as rhenium, cobalt, molybdenum, chromium, tungsten, aluminum, titanium, tantalum, hafnium, and silicon, optimized for directed solidification and heat treatment to enhance creep resistance, microstructural stability, and resistance to oxidation and corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nickel-based superalloys are used for single-crystal blades in gas turbines, then high creep resistance at elevated temperatures is achieved, but resistance to oxidation and corrosion deteriorates
Solution Approach 1:
The patent applies composite materials by combining nickel-based superalloy substrate with multi-layer protective coatings (MCrAlY undercoat and YSZ thermal barrier coating). This composite structure allows the superalloy to provide high-temperature creep resistance while the coating layers provide oxidation and corrosion protection, resolving the contradiction between mechanical strength and environmental resistance.
Solution Approach 2:
The patent optimizes the chemical composition parameters of the superalloy, specifically controlling the content of alloying elements like rhenium (4.0-6.0%), cobalt (5.0-10.0%), and chromium (3.0-6.0%) to achieve a balance between creep resistance and oxidation resistance. By adjusting these compositional parameters, the material simultaneously improves high-temperature strength and environmental stability.
2Strength
If refractory elements like rhenium are added to improve creep resistance, then high-temperature mechanical strength is enhanced, but secondary reaction zones form under the coating reducing mechanical properties
Solution Approach 1:
The patent optimizes the concentration of rhenium and other refractory elements within specific ranges (Re: 4.0-6.0%, Co: 5.0-10.0%, Cr: 3.0-6.0%) to achieve optimal creep resistance while preventing excessive element diffusion that would create harmful secondary reaction zones. This parameter optimization resolves the contradiction between improving high-temperature strength and maintaining reliability under coating.
Solution Approach 2:
The patent creates different compositional zones within the superalloy structure, with controlled distribution of refractory elements to enhance creep resistance in the matrix while limiting their concentration in regions prone to secondary reaction zone formation. This local compositional differentiation allows simultaneous achievement of high creep resistance and maintained mechanical properties under coating.
3Strength
If complex alloy chemistry is used to enhance performance, then creep resistance is improved, but microstructural stability deteriorates with formation of TCP phases
Solution Approach 1:
The patent carefully controls the chemical composition parameters, limiting the content of elements that promote TCP phase formation while maintaining sufficient creep resistance. By optimizing the balance between alloying elements (Re, Co, Cr, Mo, W) and keeping certain elements below critical thresholds, the patent achieves high creep resistance while preventing microstructural destabilization and TCP phase precipitation.
4Strength
If directional solidification is used to produce single-crystal blades, then creep resistance is enhanced, but production costs increase due to defects and scrap
Solution Approach 1:
The patent optimizes the chemical composition to improve castability and reduce defect formation during directional solidification. By adjusting alloying element contents (particularly Re, Co, and Cr within specific ranges), the material exhibits improved fluidity and reduced tendency to form freckle defects, thereby reducing scrap rates and production costs while maintaining high creep resistance.
Solution Approach 2:
The patent eliminates or minimizes harmful elements and impurities that cause defects during solidification, extracting only the necessary alloying elements in optimized quantities. This selective composition design reduces manufacturing defects and scrap while maintaining the required mechanical properties, thereby reducing production costs.
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 optimized superalloy composition improves high-temperature creep resistance, reduces sensitivity to phase instabilities, and minimizes defects like freckle grains, resulting in enhanced mechanical properties and reduced production costs.
Implementation Method 1
The single-crystal nickel-based superalloy is obtained by a directed solidification process under thermal gradient in a lost-wax casting process
Implementation Method 2
This matrix contains precipitates of hardening gamma prime phase (γ') of ordered cubic structure L12 of type Ni3Al
Implementation Method 3
A heat treatment step of redissolving the γ' phase precipitates and the γ/γ' eutectic phases which form during the solidification of the superalloy
Implementation Method 4
The deposition step is followed by a step of diffusing the undercoat into the superalloy
Implementation Method 5
inter-Diffusion phenomena occur at the microscopic scale between the nickel-based superalloy of the substrate and the metallic alloy of the underlayer
Implementation Method 6
associated with the oxidation of the underlayer, modify in particular the chemical composition, the microstructure and consequently the mechanical properties
Data Source
Figure 1
Figure 2~3
AI summary
The invention relates to a nickel-based superalloy comprising, in weight percentages, 4.0 to 5.5 % rhenium, 3.5 to 12.5 % cobalt, 0.30 to 1.50 % molybdenum, 3.5 to 5.5 % chromium, 3.5 to 5.5 % tungsten, 4.5 to 6.0 % aluminum, 0.35 to 1.50 % titanium, 8.0 to 10.5 % de tantalum, 0.15 to 0.30 % hafnium, 0.05 to 0.15 % silicon, the remainder being nickel and inevitable impurities. The invention also relates to a single-crystal blade (20A, 20B) comprising such an alloy and to a turbomachine (10) comprising such a blade (20A, 20B).