Expansion Alloy 4J29
4J29, also known as Kovar alloy, is an iron-nickel-cobalt hard glass sealing alloy. Its core advantages lie in its sealing compatibility and environmental stability, specifically:
1. **Superior Sealing Performance:** The thermal expansion coefficient in the 20-450℃ range highly matches that of borosilicate hard glass and alumina ceramics. The dense oxide film is also well-wetted by the glass, resulting in a glass-to-metal seal strength of ≥20MPa and airtightness of 1×10⁻¹¹ Pa·m³/s. This prevents cracks at the seal due to temperature fluctuations, making it a core material for sealing in vacuum electronic devices.
2. **Stable Performance Across All Temperatures:** It exhibits excellent structural stability at low temperatures; no martensitic structure appears even after 4 hours of freezing at -78.5℃. It still maintains a thermal conductivity of 12 W/m·K at -196℃, and its tensile strength remains ≥450MPa at 500℃, making it suitable for extreme temperature difference scenarios such as space and deep-sea environments.
3. **Excellent Processability and Connectivity:** It can be processed through cold rolling and cold drawing, forming various shapes such as tubes, plates, and wires, with dimensional accuracy reaching the micron level after processing. It is compatible with processes such as argon arc welding and electron beam welding, with weld strength reaching over 85% of the base material. Post-weld treatment ensures overall performance.
4. **Strong Adaptability to Multiple Scenarios:** It exhibits ferromagnetism and high magnetic permeability at room temperature, reducing electromagnetic interference and ensuring signal stability in devices such as microwave tubes. Its corrosion rate in salt spray environments is ≤0.01 mm/year, and it does not react with mercury, making it suitable for various applications including shipborne radar and mercury-containing discharge instruments.
