Ni-based Alloy Segregation Control for Large Gas Turbine Components
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Solution Overview
Problem
Ni-based heat resistant alloys face challenges in producing large-sized components due to segregation issues during solidification, limiting their application in gas turbines despite their high-temperature strength, as elements like titanium, niobium, and molybdenum tend to segregate, causing cracks and reducing productivity.
Innovation Solution
A Ni-based heat resistant alloy composition is optimized by adjusting the amounts of aluminum, titanium, niobium, and molybdenum to minimize segregation, with specific mass percent ranges for elements like carbon, chromium, molybdenum, tungsten, niobium, titanium, and iron, ensuring a parameter Ps ≥ -3.5 to reduce segregation tendencies and enhance large-sized steel ingot productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If large amounts of precipitation strengthening elements (titanium, niobium, tantalum) are added to stabilize the γ' phase and improve high-temperature strength, then the high-temperature strength is improved, but segregation occurs during solidification making it difficult to manufacture large-sized components
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ratios of alloying elements. Specifically, it limits titanium to 0.01-3.0 wt%, niobium to 0.01-5.0 wt%, and tantalum to 0.01-3.0 wt%, while maintaining aluminum at 0.5-2.0 wt% for γ' phase formation. This optimized parameter range achieves the desired high-temperature strength while minimizing segregation during solidification, enabling production of large-sized components up to 10 tons.
2Strength
If Alloy 718 is used to achieve higher strength than Alloy 706, then the strength is improved, but segregation is more liable to occur and it is difficult to produce a large-sized steel ingot
Solution Approach 1:
The patent modifies the compositional parameters of conventional Alloy 718 by reducing the overall content of strong segregating elements (titanium, niobium, tantalum) while maintaining adequate γ' phase strengthening through controlled aluminum content (0.5-2.0 wt%). This parameter adjustment achieves tensile strength of 1000 MPa or more at room temperature and 800 MPa or more at 700°C, while enabling production of large-sized ingots up to 10 tons without severe segregation.
3Volume of stationary object
If the component size is increased beyond 2-3 tons, then the gas turbine capacity is improved, but segregation occurs and cracks are generated making it difficult to produce larger products
Solution Approach 1:
The patent applies parameter changes by optimizing the alloy composition to reduce segregation tendency. It controls titanium at 0.01-3.0 wt%, niobium at 0.01-5.0 wt%, and tantalum at 0.01-3.0 wt%, with aluminum at 0.5-2.0 wt% to form sufficient γ' phase. This composition enables production of large-sized ingots up to 10 tons with uniform microstructure, preventing crack formation during solidification and forging, and achieving reliability suitable for large gas turbine components.
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 alloy composition allows for the production of large-sized components with high-temperature strength, reducing segregation and improving gas turbine efficiency by maintaining excellent mechanical properties and preventing cracks, enabling the manufacture of larger gas turbine components like turbine discs.
Implementation Method 1
A γ' phase (Ni 3 Al) is a main precipitation strengthening phase, and the strength thereof increases depending on an increase of its temperature
Implementation Method 2
The Ni-based alloy contains large amounts of solid-solution strengthening elements such as tungsten, molybdenum or cobalt
Data Source
Figure 1~2
AI summary
A Ni-based heat resistant alloy has a composition of, by mass percent, carbon: 0.001 to 0.1%, chromium: 16 to 22%, aluminum: 0.5 to 1.5%, molybdenum: 0.1 to 2.0%, tungsten: 0.1 to 6.0%, niobium: 3.5 to 5.5%, titanium: 0.8 to 3.0%, iron: 16 to 20%, and the balance being nickel and inevitable impurities. A parameter Ps indicating a segregation tendency is in a range of Ps ≥ -3.5. The parameter Ps is represented by Formula (1). Ps=1.05×Al content+0.6×Ti content-0.8×Nb content-0.3×Mo content