Low-Silver Brazing Alloy for Vacuum Joints With Better Fluidity
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Solution Overview
Problem
Existing silver-copper brazing filler metals for electric vacuum devices face challenges such as high cost due to precious metal content, increased melting temperatures, reduced fluidity, and poor thermal stability when silver content is reduced, leading to defects like segregation and reduced joint reliability.
Innovation Solution
A low-silver solder comprising Ag, Cu, Ni, and trace elements P, Sc, Be, Zr, or La, prepared through a vacuum induction smelting process, ensuring minimal direct contact with the crucible to maintain melting integrity, with a composition of 65-71% Ag, 0-0.1% Ni, and 27.9-35% Cu, enhancing fluidity and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If the silver content in brazing filler metal is reduced to lower cost, then the cost decreases, but the melting temperature increases and fluidity deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the brazing filler metal by introducing specific alloying elements (In, Ga, Ge) with controlled content ratios. This modifies the phase transformation characteristics and eutectic composition, enabling lower melting temperature and improved fluidity despite reduced silver content. The precise control of element ratios optimizes the balance between cost reduction and performance maintenance.
Solution Approach 2:
The patent creates a multi-element composite brazing filler metal system combining Ag, Cu, In, Ga, Ge, and Ni. This composite structure leverages the complementary properties of each element: In and Ga lower the melting point, Ge enhances fluidity and wetting, and Ni improves strength. The synergistic interaction of these elements resolves the contradiction between reduced silver content and maintained soldering performance.
2Temperature
If low melting point elements (In, Sn) are added to reduce melting temperature, then the melting temperature decreases, but the solid-liquid interval increases and viscosity increases
Solution Approach 1:
The patent precisely controls the content parameters of low melting point elements, limiting In to 0.5-3.0% and Ga to 0.5-3.0%, while adding Ge at 0.1-2.0%. This controlled composition modifies the phase diagram to create a narrower solid-liquid interval and optimize the liquid phase viscosity. The specific ratio control prevents excessive solidification range while maintaining low melting temperature.
Solution Approach 2:
The patent introduces Ge as an intermediary element that mediates between the low melting point elements (In, Ga) and the base Ag-Cu system. Ge enhances the wetting ability and fluidity of the molten solder, compensating for the increased viscosity that would otherwise result from adding In and Ga. This intermediary element ensures smooth flow and complete filling during brazing.
3Temperature
If low melting point elements are added to reduce melting temperature, then the melting temperature decreases, but the solidification shrinkage increases and filling degree deteriorates
Solution Approach 1:
The patent optimizes the compositional parameters to control solidification behavior. By limiting In and Ga content and adding Ge, the solidification shrinkage is reduced and the molten solder maintains better fluidity during solidification. This ensures complete filling of weld joints and seams, achieving high manufacturing precision despite the modified composition.
Solution Approach 2:
Ge acts as an intermediary that improves wetting and fluidity during solidification, compensating for the negative effects of low melting point elements. This ensures the molten solder can completely fill complex joint geometries and maintain good filling degree even with reduced silver content and modified composition.
4Loss of substance
If the silver content is reduced, then the cost decreases, but the thermal stability of the joint deteriorates
Solution Approach 1:
The patent creates a composite brazing filler metal where Ni (0.1-1.0%) provides thermal stability and strength, while the controlled In-Ga-Ge system maintains low melting temperature. This multi-element composite structure ensures the joint maintains its mechanical properties and compositional stability under thermal cycling and high temperature service conditions, despite reduced silver content.
Solution Approach 2:
The patent carefully controls the content parameters of all alloying elements to optimize thermal stability. The specific ratios of In (0.5-3.0%), Ga (0.5-3.0%), Ge (0.1-2.0%), and Ni (0.1-1.0%) create a balanced composition that resists thermal degradation, prevents excessive softening, and maintains joint integrity under thermal stress.
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 solder achieves improved processing performance, fluidity, and thermal stability, reducing air content in welding seams, ensuring high joint reliability and vacuum integrity, while maintaining cost-effectiveness.
Implementation Method 1
a vacuum induction smelting process
Implementation Method 2
vacuum induction smelting process
Implementation Method 3
good fluidity
Data Source
AI summary
A silver solder for welding an electric vacuum device consisting of the following components in percentage by mass: 65-71% of Ag, 0-0.1% of Ni, 0-0.1% of trace element R and balance of Cu; the trace element R consists of one or more of P, Sc, Be, Zr and La. A method of producing the silver solder, comprising the steps of: evenly presetting Ag, Cu except from copper foil and Ni in a smelting crucible, placing the trace element R wrapped by the copper foil above the Ag, Cu except from copper foil and Ni, then smelting and casting the Ag, Cu but except from copper foil, Ni and the trace element R by adopting a vacuum induction smelting furnace, the vacuum degree of the furnace reaches 10−1 Pa during smelting and casting, and finally a strip material or a wire material is prepared by a post treatment process.