Low-Melting Nickel Braze Alloy Composition for Low-Temperature Joining
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Solution Overview
Problem
Conventional brazing techniques for nickel-based alloys and stainless steels require high temperatures, leading to unwanted microstructural changes, such as grain growth and phase coarsening, which degrade mechanical strength and corrosion resistance, and are often compromised by high vapor pressure of phosphorus in low-melting Ni-P alloys.
Innovation Solution
Development of low-melting nickel-iron-based filler alloys with compositions like Ni-aFe-bP-cB-dSi-eC-fX, where X includes elements like Cu, Nb, and rare earths, with specific atom percentages to achieve liquidus and solidus temperatures below 950°C, minimizing intermetallic phase formations and allowing brazing at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional high-temperature brazing is used, then strong metallurgical bonding is achieved, but grain growth and phase coarsening occur which degrade mechanical strength and corrosion resistance
Solution Approach 1:
The invention changes the temperature parameter by developing filler alloys with liquidus temperatures below 950°C, enabling brazing at lower temperatures (typically 50°C above liquidus) to prevent grain growth and phase coarsening while maintaining strong bonding
Solution Approach 2:
The invention uses composite alloy systems combining Ni-Fe base with multiple melting-point-depressing elements (P, B, Si, C) and optional modifiers (Cu, Nb, rare earths) to achieve both low melting temperature and strong bonding capability
2Temperature
If low-melting Ni-P alloys are used, then brazing temperature is reduced, but phosphorus vapor pressure causes depletion and precipitation of solid nickel
Solution Approach 1:
The invention transitions from binary Ni-P to quaternary/quinary Ni-Fe-P-B-Si-C systems with controlled compositions (10-25 atom% combined P, B, Si, C) to reduce phosphorus concentration and its vapor pressure while maintaining low melting temperature through synergistic melting-point-depressing effects
Solution Approach 2:
The invention changes the compositional parameters by limiting P content and adding Fe along with B, Si, and C to balance melting temperature, vapor pressure, and bonding performance
3Strength
If conventional filler alloys are used, then good bonding is achieved, but high brazing temperature causes recrystallization and excessive grain growth
Solution Approach 1:
The invention changes the temperature parameter by formulating filler alloys with liquidus temperatures below 950°C, enabling brazing at lower temperatures to minimize recrystallization and grain growth in the base material while maintaining strong bonding
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 new filler alloys provide robust metallurgical bonding with reduced recrystallization and grain growth, enhancing tensile and shear strengths while maintaining corrosion resistance, and are cost-effective with improved compatibility with iron-based alloys.
Implementation Method 1
forming metallurgical bonds, e.g., by interdiffusion of filler-alloy elements with those of the base material
Implementation Method 2
the materials are heated to melt and react with enclosed filler alloys
Implementation Method 3
their microstructures and properties are affected by diffusion of the alloy and impurity elements and by grain growth and precipitate-phase coarsening
Implementation Method 4
grain growth and precipitate-phase coarsening
Implementation Method 5
their high P-concentrations generate a high vapor pressure of phosphorus during brazing. The vaporization results in a depletion of phosphorus in the filler alloy
Data Source
AI summary
A braze alloy composition includes the formula:NiaFebPcBdSieCfXg wherein X is selected from the group consisting of Cu, Nb, Hf, Mo, W, V, Ta, Y, La, rare earth elements, Al, Ru, Pd, Cr, Mn, Co, Be, and mixtures thereof, a, b, c, d, e, f, and g are atom % of, respectively, Ni, Fe, P, B, Si, C, and X, and wherein 75≤((a+b)−g)≤90, a>b, 10≤c+d+e+f≤25, and g<10.