1.3981 / UNS K94610
A nickel-iron-cobalt controlled-expansion alloy containing 29% nickel. Its coefficient of expansion, which decreases with rising temperature to the inflection point, matches the expansion rate of borosilicate glasses and alumina ceramics. Used for glass-to-metal seals in applications requiring high reliability or resistance to thermal shock. Examples are high-power transmitting valves, transistor leads and headers, integrated-circuit lead frames, and photography flash bulbs.