Kovar

Kovar is an iron nickel cobalt alloy with low coefficient of linear expansion, low thermal conductivity, and high resistance. By using methods such as stamping and cutting, Kovar alloy can be made into products with complex shapes. Kovar alloy is easier to melt and braze, but it is more difficult to machine than nickel because of its high toughness.

The expansion coefficient of Kovar alloy is matched with that of silicon boron hard glass and ceramics. The kovar glass seal can be baked to 460 ℃. A typical Kovar alloy contains 53% to 54% Fe, 28% to 29% Ni, 17% to 18% Co,<0.5% Mn, 0.2% Si, and a total of<0.25% Al, Mg, Zr, and Ti.

Kovar can be brazed and fused using soft or hard solder, and can also be molded or machined after annealing. The commonly used welding method in vacuum technology is copper brazing in a hydrogen furnace.

Kovar alloy has excellent corrosion resistance and can generate dense and firm films during oxidation. Kovar alloy is very stable for mercury and can corrode in a mixture of dilute nitric acid and hydrochloric acid. Kovar does not react with mercury or mercury vapor. Kovar alloy exhibits ferromagnetism below 453 ℃.