Multi-layered Brazed Feed-through Assembly for Metal-Ceramic Joints
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Solution Overview
Problem
Metal-ceramic joints in devices like X-ray tubes are prone to failure due to thermal expansion and residual stresses from conventional brazing processes, which also result in poor wetting and leaky joints between vacuum and atmospheric chambers.
Innovation Solution
A multi-layered brazed joint is formed using a specific arrangement of braze filler materials around a metal component passed through a ceramic insulator, with a hollow member and ceramic member, subjected to multiple brazing temperature cycles, utilizing Fe-Ni alloy and Alumina ceramics with metallization for enhanced bonding and stress management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional brazing process is used to join metal and ceramic, then bonding is achieved, but residual stresses and thermal expansion mismatches cause joint failure
Solution Approach 1:
The invention introduces an intermediate layer segmented into multiple functional zones: a first intermediate layer of metal powder and glass powder for stress management, and a second intermediate layer for wetting enhancement. This segmentation allows each layer to address specific issues (thermal expansion mismatch and wetting) independently, preventing joint failure while maintaining strength.
Solution Approach 2:
The invention uses an intermediate layer composed of metal powder and glass powder as a mediator between the ceramic insulator and the metal component. This intermediate layer accommodates thermal expansion differences and creates a gradual transition in material properties, reducing residual stresses and preventing joint failure during thermal cycling.
2Strength
If braze material is melted between ceramics, then joining is achieved, but poor wetting results in poor joint quality
Solution Approach 1:
The invention applies a metallization coating to the ceramic surface before brazing as a preliminary action. This coating enhances the wettability of the ceramic surface by the braze material, ensuring proper wetting and adhesion. The preliminary metallization prevents poor wetting issues and ensures consistent joint quality without requiring complex manufacturing adjustments.
3Reliability
If single-layer brazing is used, then simple process is maintained, but leak-proof joint between vacuum and atmospheric chambers cannot be achieved
Solution Approach 1:
The invention segments the brazing joint into multiple functional layers: a first intermediate layer for stress management and a second intermediate layer for wetting enhancement. This segmentation enables the joint to simultaneously achieve leak-proof sealing between vacuum and atmospheric chambers while managing thermal stresses, without requiring overly complex structural designs.
4Manufacturing precision
If conventional brazing is used, then process simplicity is maintained, but flux entrapment and discontinuous fillet occur
Solution Approach 1:
The invention changes the material parameters of the intermediate layer by using specific compositions of metal powder and glass powder with controlled particle size distributions. This parameter optimization ensures complete filler material distribution, prevents flux entrapment, and creates continuous fillets, achieving high manufacturing precision without significantly increasing process complexity.
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 creates a leak-proof joint with minimal residual stresses, capable of withstanding high temperatures and thermal cycles, ensuring reliable performance in medical devices like X-ray tubes with a leak rate of <3×10−9-mbar lit./sec and flexibility to adjust for stress.
Implementation Method 1
The molten metal flows and fills in the gaps by capillary action and is allowed to cool to form a brazed joint
Implementation Method 2
Filler metal is heated above its melting temperature and distributed between two or more close-fitting parts
Implementation Method 3
Due to the thermal expansion occurring between the metal and ceramic joints, these joints are prone to failures or inconsistent performance
Data Source
AI summary
A feed through assembly has a metal component passed through a ceramic insulator, and a multi-layered joint brazed to the ceramic insulator and the metal component to form the assembly. The multi-layered joint includes a first portion of braze filler material placed around the metal component and a hollow member of predetermined shape placed around the metal component. A flange is provided at a first end of the hollow member, wherein the flange rests on the first portion of braze filler material. The multi-layered joint has a second portion of braze filler material placed around the hollow member and seated onto the flange. A ceramic member of predetermined shape is placed around the hollow member which rests on the second portion of braze filler material. A third portion of braze filler material is placed around the metal component and seated onto a second end of the hollow member.