Co-Based Alloy High-Temperature Strength and Hot Workability
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Solution Overview
Problem
Conventional Co-based alloys exhibit lower high-temperature strength and inferior hot workability compared to Ni-based alloys, primarily due to the lack of effective γ'-type intermetallic compounds, which hampers their application in high-temperature environments.
Innovation Solution
A Co-based alloy with a predetermined composition, including specific ranges of Al, W, Cr, and C, undergoes homogenizing heat treatment and solution heat treatment followed by aging, precipitating a Co3(Al, W) strengthening phase and carbides in the grain boundaries, enhancing high-temperature strength and ductility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Al and W are added to Co-based alloy to generate γ' phase for improving high-temperature strength, then high-temperature strength is improved, but harmful phases precipitate during heat treatment which significantly decrease hot workability
Solution Approach 1:
The patent optimizes the composition parameters by strictly controlling Al content to 2.0-5.0 mass% and W content to 10.0-20.0 mass%, along with specific ranges of Cr, Ni, and other elements. This parameter optimization ensures that the alloy achieves sufficient γ' phase precipitation for high-temperature strength while suppressing harmful phase formation, thereby resolving the contradiction between strength improvement and hot workability maintenance
Solution Approach 2:
The patent creates a composite microstructure consisting of γ matrix phase, γ' (Co3(Al,W)) intermetallic strengthening phase, and controlled carbide precipitates. This multi-phase composite structure provides both the high-temperature strength from γ' precipitation and the hot workability by controlling the morphology and distribution of phases through optimized composition and heat treatment processes
2Strength
If excessive W is contained in Co-based alloy, then high-temperature strength may be improved through γ' phase, but harmful phases are generated within grains and grain boundaries which significantly decrease hot workability
Solution Approach 1:
The patent optimizes the composition parameters by strictly controlling Al content to 2.0-5.0 mass% and W content to 10.0-20.0 mass%, along with specific ranges of Cr, Ni, and other elements. This parameter optimization ensures that the alloy achieves sufficient γ' phase precipitation for high-temperature strength while suppressing harmful phase formation, thereby resolving the contradiction between strength improvement and hot workability maintenance
Solution Approach 2:
The patent promotes localized carbide precipitation at grain boundaries through optimized C content (0.03-0.10 mass%) and Cr content (8.0-15.0 mass%). This creates local strengthening zones at grain boundaries that suppress harmful phase formation in critical regions while maintaining overall alloy composition for γ' phase development, thus improving hot workability without sacrificing high-temperature strength
3Reliability
If conventional Co-based alloy is used for high-temperature applications, then corrosion resistance and ductility are improved, but high-temperature strength is lower than Ni-based alloy
Solution Approach 1:
The patent creates a composite microstructure consisting of γ matrix phase, γ' (Co3(Al,W)) intermetallic strengthening phase, and controlled carbide precipitates. This multi-phase composite structure provides both the high-temperature strength from γ' precipitation and maintains the corrosion resistance and ductility characteristics of Co-based alloys, resolving the contradiction between strength and reliability
Solution Approach 2:
The patent optimizes the composition parameters by strictly controlling Al content to 2.0-5.0 mass% and W content to 10.0-20.0 mass%, along with specific ranges of Cr, Ni, and other elements. This parameter optimization ensures that the alloy achieves sufficient γ' phase precipitation for high-temperature strength while maintaining the corrosion resistance and ductility inherent to Co-based alloys
4Reliability
If Co-based alloy is used instead of Ni-based alloy for high-temperature applications, then corrosion resistance and ductility are improved, but hot workability becomes inferior to Ni-based alloy
Solution Approach 1:
The patent optimizes the composition parameters by strictly controlling Al content to 2.0-5.0 mass% and W content to 10.0-20.0 mass%, along with specific ranges of Cr, Ni, and other elements. This parameter optimization ensures that the alloy achieves sufficient γ' phase precipitation for high-temperature strength while suppressing harmful phase formation, thereby resolving the contradiction between strength improvement and hot workability maintenance
Solution Approach 2:
The patent promotes localized carbide precipitation at grain boundaries through optimized C content (0.03-0.10 mass%) and Cr content (8.0-15.0 mass%). This creates local strengthening zones at grain boundaries that suppress harmful phase formation in critical regions while maintaining overall alloy composition for γ' phase development, thus improving hot workability without sacrificing high-temperature strength
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 high-temperature strength and ductility comparable to or exceeding that of Ni-based alloys, with improved hot workability and creep rupture properties, making it suitable for high-temperature applications.
Implementation Method 1
when the alloy includes predetermined amounts of Al and W and is subjected to homogenizing heat treatment
Implementation Method 2
when the alloy is subjected to solution heat treatment and aging treatment under predetermined conditions after hot working, a Co3(Al, W) strengthening phase (γ' phase) is precipitated
Implementation Method 3
when the alloy is subjected to solution heat treatment and aging treatment under predetermined conditions after hot working
Implementation Method 4
when a predetermined amount of carbon is added to the Co-based alloy containing predetermined amounts of Al, W and Cr, carbide containing W and/or Cr is precipitated in addition to the γ' phase after the aging treatment
Data Source
AI summary
A Co-based alloy containing not less than 0.001 mass% and less than 0.100 mass% of C, not less than 9.0 mass% and less than 20.0 mass% of Cr, not less than 2.0 mass% and less than 5.0 mass% of A1, not less than 13.0 mass% and less than 20.0 mass% of W, and not less than 39.0 mass% and less than 55.0 mass% of Ni, with the remainder being made up by Co and unavoidable impurities, wherein the contents of Mo, Nb, Ti and Ta which are included in the unavoidable impurities are as follows: Mo < 0.010 mass%, Nb < 0.010 mass%, Ti < 0.010 mass%, and Ta < 0.010 mass%.