How to Achieve Reliable Bonding between Ceramics and Metals

Bonding between ceramics and metals is a key technology in aerospace, electronics, medical and other fields. However, they differ significantly in terms of thermal expansion coefficients, types of chemical bonds, etc., so direct bonding is prone to cracking or detachment. Currently, the mainstream methods can be divided into the following three categories:

1. Mechanical connection methods

Fixation is achieved through physical structures, suitable for non-sealed or low-stress scenarios.

Threaded/snap connection: Drilling and tapping are performed on ceramic parts, which are then fastened with metal bolts. It is necessary to avoid local stress concentration on the ceramics.

Shrink fit assembly: Utilizing the difference in thermal expansion and contraction, metal parts are heated before being sleeved over ceramics. After cooling, an interference fit is formed, such as in spark plug manufacturing.

Advantages: Simple operation and low cost.

Limitations: Not resistant to high temperature and pressure; prone to loosening after long-term use.

2. Interlayer-assisted bonding

Transition materials are introduced to relieve interface stress and improve bonding strength.

Active metal brazing: Filler metals containing titanium and zirconium (e.g., Ag-Cu-Ti) are used, which undergo chemical reactions with ceramics at high temperatures to form a transition layer. For example, the bonding of alumina and copper in electronic packaging.

Nanometal paste: Nano-silver/copper particles are coated on the ceramic surface, forming a porous metal layer after sintering, which is then brazed with metal parts. It is suitable for aluminum nitride substrates.

Key points: Precise control of temperature (usually 800~900℃) and atmosphere (vacuum or inert gas) is required.

3. Direct chemical bonding technology

Atomic-level bonding is promoted through surface treatment.

Laser-activated welding: Lasers are used to clean the ceramic surface and generate active oxides, which are then bonded with molten metal. For example, the bonding of ZrO₂ and titanium alloys in aerospace components.

Plasma spraying: Metal powders are sprayed at high speed onto a roughened ceramic surface to form a mechanical interlocking structure, commonly used in artificial joint coatings.

Future trends: Low-temperature bonding technologies (such as ultrasonic-assisted brazing) and composite interlayer designs (gradient thermal expansion materials) are research hotspots.

Summary: The selection of bonding methods needs to comprehensively consider working conditions, cost, and material properties. Active brazing and nano-modification are currently the most mature solutions.