Ni Base Forged Alloy Composition for Gas Turbine Forgeability
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Solution Overview
Problem
Ni base forged alloys face challenges in achieving high-temperature strength and segregation properties suitable for large-sized components, as solid solution and precipitation strengthening elements tend to segregate during solidification, making it difficult to manufacture large-sized members with excellent forgeability and miniaturized crystal grains.
Innovation Solution
An Ni base forged alloy with specific composition ranges, including Al, Cr, Fe, Nb, Ti, W, B, C, and Mo, is developed, where the solid solution temperature of the precipitation strengthening phase is ≤970°C, and the difference in solid solution temperature between the δ-phase and precipitation strengthening phase is ≥50°C, enhancing forgeability and suppressing crystal grain coarsening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid solution strengthening elements (W, Mo, Co) and precipitation strengthening elements (Al, Ti, Nb) are added to improve high-temperature strength, then the high-temperature strength is improved, but the elements are apt to be segregated during solidification making it difficult to manufacture large-sized members
Solution Approach 1:
The invention changes the compositional parameters by precisely controlling the content ranges of Al (0.5-1.5%), Ti (0.8-3.0%), Nb (3.5-5.5%), W (0.1-6.0%), Mo (0.1-2.0%), and other elements. This parameter optimization balances the competing requirements: maintaining sufficient precipitation strengthening elements for high-temperature strength while limiting elements that cause severe segregation, enabling successful casting of large-sized members up to 3 tons or more
Solution Approach 2:
The invention creates a composite alloy system combining multiple strengthening mechanisms: solid solution strengthening (W, Mo, Co), precipitation strengthening (γ'-phase Ni3Al, γ"-phase Ni3Nb), and grain boundary strengthening (δ-phase). This composite approach allows the alloy to achieve high-temperature strength comparable to or exceeding Alloy 718 while improving segregation resistance through the synergistic effect of multiple strengthening phases
2Strength
If Alloy 718 is used for large-sized members, then excellent high-temperature strength is achieved, but the segregation property is reduced and manufacturing method of controlling the solidification speed is required
Solution Approach 1:
The invention modifies the compositional parameters compared to Alloy 718 by adjusting Al (0.5-1.5% vs. typically 0.5-1.0%), Ti (0.8-3.0% vs. typically 0.5-1.0%), Nb (3.5-5.5% vs. typically 5.0-6.0%), and adding specific ranges of Cr (16-22%), Fe (16-20%), W (0.1-6.0%), and Mo (0.1-2.0%). These parameter changes optimize the balance between strength and segregation resistance, allowing large-sized members to be manufactured without complex solidification speed control
Solution Approach 2:
The invention converts the potential harm of segregation into a benefit by carefully selecting element combinations where certain elements (Cr, Fe) have low segregation tendency and can act as diluents to reduce the overall segregation of strengthening elements. The controlled addition of W and Mo, which have different segregation behaviors, further helps to balance the compositional stability during solidification
3Weight of stationary object
If large-sized material exceeding 5 tons is manufactured, then the solidification condition has restriction in order to continue stable operation, but there are a lot of Ni base alloys to which it cannot be applied
Solution Approach 1:
The invention changes the alloy composition parameters to enable applicability to large-sized members up to 3 tons or more. The specific composition ranges (Al: 0.5-1.5%, Cr: 16-22%, Fe: 16-20%, Nb: 3.5-5.5%, Ti: 0.8-3.0%, W: 0.1-6.0%, Mo: 0.1-2.0%) are optimized to ensure stable solidification conditions, reduced segregation, and consistent mechanical properties throughout the large volume, expanding the applicability beyond conventional alloy limits
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 alloy achieves excellent high-temperature strength and segregation properties, enabling the production of large-sized members with improved forgeability and miniaturized crystal grains, suitable for applications like gas turbines, with a yield stress ≥1000 MPa at 500°C, and effective in manufacturing large-sized components up to 3 tons or more.
Implementation Method 1
a γ'-phase (gamma prime phase) made of Ni 3 Al and a γ"-phase (gamma double prime phase) made of Ni 3Nb which are the precipitation strengthening phases can be precipitated to matrix phase finely and innumerably
Implementation Method 2
it is considered that the cause bringing about the segregation is that solute elements are distributed in solid-liquid interface unevenly, so that difference in density in molten metal is changed
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
An Ni base forged alloy is easy to make hot forging and miniaturization of crystal grains while excellent high-temperature strength and segregation property are compatible. The Ni base forged alloy has solid solution temperature of a precipitation strengthening phase lower than or equal to 970°C, difference in the solid solution temperature between a δ-phase and the precipitation strength phase larger than or equal to 50°C, Al of 0.5 to 1.0%, Cr of 17 to 21%, Fe of 17 to 19%, Nb of 4.5 to 5.5%, Ti of 0.8 to 1.3%, W of 3.0 to 6.0%, B of 0.001 to 0.03%, C of 0.001 to 0.1 % and Mo of 1.0% or less in mass percentage [%] and remainder made of Ni and inevitable impurities.