Nickel-Cobalt Alloy High-Temperature Stability
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Solution Overview
Problem
Nickel alloys like Alloy 718 have limited high-temperature application due to low γ" phase stability, while Waspaloy suffers from poor hot formability and limited forging temperature windows due to high y' phase solution temperatures, restricting their use in high-temperature gas turbines.
Innovation Solution
A nickel-cobalt alloy with specific composition ranges for Co, Cr, Mo, Nb, Ta, Al, Ti, and other elements, optimizing γ'-solvus and δ-solvus temperatures to achieve high structural stability and improved formability, allowing for higher temperature applications without surface cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Alloy 718 is used with γ" phase for high strength, then strength properties are improved, but application temperature is limited to 650°C due to γ" phase transformation into δ phase
Solution Approach 1:
The patent changes the chemical composition parameters by adding cobalt (5-15 wt%) and adjusting Al, Ti, and Nb contents to modify the phase transformation temperatures. This shifts the γ" to δ transformation temperature to above 750°C, enabling higher application temperatures while maintaining strength through γ" phase precipitation at service temperature.
2Temperature
If Waspaloy alloy uses high Al and Ti proportions to achieve structural stability at higher temperatures, then application temperature increases to 750°C, but hot formability deteriorates due to poor formability during forging
Solution Approach 1:
The patent optimizes the balance between Al (1.0-2.5 wt%), Ti (0.5-1.5 wt%), and Co (5-15 wt%) content to achieve a γ'-solvus temperature between 950-1050°C. This creates a sufficient temperature window (ΔT ≥ 100°C) between γ'-solvus and δ-phase precipitation temperature, enabling hot forging at temperatures where γ' phase does not precipitate, thus maintaining good hot formability while achieving structural stability at 750°C.
3Stability of the object's composition
If Waspaloy alloy uses high γ' phase solution temperature for high-temperature stability, then structural stability at 750°C is achieved, but forging temperature window becomes restricted due to surface cracks from γ' phase precipitation
Solution Approach 1:
The patent adjusts the γ'-solvus temperature to 950-1050°C through optimized Al, Ti, and Co content, creating a temperature window of at least 100°C between the γ'-solvus and δ-phase precipitation temperatures. This allows forging to be performed at temperatures below γ'-solvus where γ' phase remains soluble, preventing surface cracks, while still achieving structural stability at 750°C through controlled γ' phase precipitation after forging.
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 exhibits enhanced structural stability up to 100 K higher temperatures than Alloy 718 and improved formability compared to Waspaloy, enabling its use in critical components like turbine disks and blades with reduced manufacturing costs and increased durability.
Implementation Method 1
Two precipitation phases are essentially responsible for the high strength properties of the nickel alloy Alloy 718. This is, on the one hand, the γ" phase Ni 3 Nb and, on the other hand, the y' phase Ni 3 (Al, Ti).
Implementation Method 2
above this temperature the metastable γ" phase transforms into the stable δ phase. This transformation causes the material to lose its creep resistance properties.
Implementation Method 3
At forging temperatures in the range of the precipitation temperature of the δ phase, small proportions of precipitation in the δ phase result in grain refinement. This small grain of the billet structure remains or becomes even finer-grained due to hot forming
Data Source
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AI summary
The invention relates to a Ni-Co alloy, comprising 30 to 65 wt% Ni, > 0 to max. 10 wt% Fe, > 12 to < 35 wt% Co, 13 to 23 wt% Cr, 1 to 6 wt% Mo, 4 to 6 wt% Nb + Ta, > 0 to < 3 wt% Al, > 0 to < 2 wt% Ti, > 0 to max. 0.1 wt% C, > 0 to max. 0.03 wt% P, > 0 to max. 0.01 wt% Mg, > 0 to max. 0.02 wt% B, > 0 to max. 0.1 wt% Zr, which fulfils the following requirements and criteria: a) 900°C <γ' solvus temperature < 1030°C with 3 at% < Al+Ti (at%) < 5.6 at% and 11.5 at% < Co < 35 at%; b) stable microstructure after 500 h of ageing annealing at 800°C with a ratio Al/Ti > 5 (on the basis of the contents in at%).