Cobalt Alloy Fluid Contact Member for Corrosion-Resistant Overlays
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Solution Overview
Problem
Fluid contact members in power generation facilities, such as valve seats, face challenges with corrosion resistance due to the formation of compound phases like eutectic carbide during high-temperature deposition, leading to selective corrosion and reduced durability.
Innovation Solution
A fluid contact member with a cobalt-based alloy phase and a compound phase containing chromium carbide, where the average interval of secondary arms in the dendrite is 5 μm or less, is developed to enhance corrosion resistance by preventing excessive erosion and void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high temperature melting is used to overlay deposited metal on substrate, then the deposited metal can be successfully deposited, but the compound phase crystallized in dendrite arm space has inferior durability and wear resistance
Solution Approach 1:
The invention changes the cooling rate parameter during solidification to control dendrite arm spacing. By increasing the cooling rate, the dendrite arm spacing is reduced to 5 μm or less, which prevents the formation of harmful compound phases in the arm spaces and improves the durability and wear resistance of the deposited metal layer.
Solution Approach 2:
The invention creates a specific microstructure where the dendrite arm spacing is controlled to be 5 μm or less throughout the deposited metal layer. This local structural characteristic prevents compound phase formation in the arm spaces, thereby improving the overall reliability and wear resistance of the coating.
2Stability of the object's composition
If compound phase is formed in dendrite arm space during cooling, then the microstructure is formed as expected from casting, but selective corrosion and erosion damage occur frequently
Solution Approach 1:
The invention changes the cooling rate parameter to control dendrite arm spacing. By increasing the cooling rate, the dendrite arm spacing is reduced to 5 μm or less, which prevents the formation of harmful compound phases in the arm spaces and improves the durability and wear resistance of the deposited metal layer.
Solution Approach 2:
The invention converts the harmful effect of compound phase formation into a beneficial outcome by controlling the dendrite arm spacing. The rapid cooling that would normally cause harmful compound phases instead creates a fine dendritic structure without harmful inclusions, transforming the solidification process into a beneficial refinement mechanism.
3Reliability
If frequent inspection and repair work is performed to maintain corrosion resistance, then the corrosion damage can be managed, but the labor of maintenance work becomes large
Solution Approach 1:
The invention performs preliminary action by controlling the dendrite arm spacing during the deposition process to prevent harmful compound phase formation. This preventive measure eliminates the need for frequent maintenance and repair work, as the deposited metal layer is inherently resistant to selective corrosion and erosion from the outset.
Solution Approach 2:
The invention makes the deposited metal layer self-protecting by creating a microstructure that inherently resists corrosion and erosion. The fine dendritic structure with spacing of 5 μm or less automatically prevents compound phase formation, eliminating the need for external maintenance interventions.
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 solution significantly improves corrosion resistance and wear resistance, reducing the need for frequent maintenance and inspection by minimizing corrosion progression and erosion damage.
Implementation Method 1
a dendrite (a base part) is crystallized out during cooling from a molten state to a solid state
Implementation Method 2
a compound phase such as eutectic carbide or eutectic boride is formed in an arm space of the dendrite
Data Source
AI summary
To provide a fluid contact member whose corrosion resistance is particularly further improved than that in the related art. In order to solve this problem, a fluid contact member 10 includes a fluid contact portion 1 configured to be in contact with a fluid, the fluid contact portion 1 has a cobalt-based alloy phase 2 having a dendrite, and a compound phase 3 formed in an arm space of the dendrite and containing chromium carbide, and among a plurality of secondary arms 5 extending from one primary arm 4 constituting the dendrite, an average interval between adjacent secondary arms 5 is 5 μm or less. At this time, the average interval is preferably 3 μm or less. Further, the compound phase 3 is preferably formed discontinuously in the dendrite arm space.