Introduction
- Kovar alloy (equivalent to GB 4J29, ASTM F15, UNS K94610) is an iron‑base sealing alloy containing 29 % nickel and 17 % cobalt, specially designed for hard‑glass-to‑metal seals. Its coefficient of thermal expansion from 20 °C to 450 °C closely matches that of hard glass, ensuring a reliable, stress‑free seal. The alloy also boasts a high Curie point and excellent structural stability at low temperatures. A dense, adherent oxide layer forms naturally on its surface, making it easy to weld or braze. With good ductility and machinability, Kovar is widely used in vacuum‑tube components, cathode‑ray tubes, switches, transistors, sealing plugs, and relay housings. The cobalt content further enhances its wear resistance.
- For sealing to molybdenum‑based glasses, Kovar parts are typically gold‑plated to improve bond strength.
- 4J29 / K94610 / Kovar / FeNi29Co17 is an iron–nickel–cobalt based, controlled‑expansion sealing alloy—commonly known as Kovar. Its chief attribute is a low coefficient of thermal expansion matched to that of glass or ceramics, ensuring that thermal stresses are minimized during the sealing process.
Chemical Composition
- Ni: 29%
- Co: 17%
- Fe: Remainder
Alloy Standard
- ASTM: K94610 / Alloy 29-17 / ASTM F15
- France: Dilver P0 / Dilver P1
- Germany: Vacon 12 / Silvar 48
- UK: cNilo K / Teleaseal
- USA: Kovar / Rodar / Techallony Glasseal29-17
- Japan: KV-1 / KV-2 / KV-3
- Russia: 29НК / 29НК-ВИ
Average Coefficient of Linear Expansion
- 4.6～5.2 10⁻⁶/℃ (20～400°C)
- 5.1～5.5 10⁻⁶/℃ (20～450°C)
- Heat to temperature of 900±20℃ in the hydrogen, hold for 1h; re-heat to 1100±20℃, hold for 15 min.; cooled to 200℃ at a rate less than 5℃/min
Application
- It is primarily used for the hermetic sealing of electronic components, vacuum tubes, displays, and other precision electronic devices.
- This ensures a reliable bond between metal and glass or ceramic, preventing failures due to thermal stress and environmental contaminants.
Alloy Forms
- Strip
- Sheet
- Rod / Bar
- Wire
