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This alloy belongs to precision alloy, also known as kovar. It is an alloy of iron, nickel and cobalt. Generally, it contains 29% nickel, 18% cobalt and the rest is iron. The coefficient of expansion is reduced by the addition of cobalt, which is close to that of molybdenum and hard glass. It is suitable for matching sealing with hard glass. During the sealing process, there is an oxide layer of oxide drill on the surface, and cobalt oxide is easily dissolved in glass to form a rat gray sealing surface. When the oxygen is insufficient, the sealing surface is silvery white as the metal itself because almost all the oxide layer dissolves into the glass. Although there is no air leakage, the strength is very poor. When the oxidation is excessive, it will be dark gray or even black due to the thick oxide layer, which is easy to cause air leakage.Best seller 1015 low carbon steel ball
The advantage of Kovar is that the curve of expansion coefficient with temperature almost coincides with that of Molybdenum Group glass. Therefore, when sealing with Molybdenum Group glass, its reliability is higher, which makes the annealing process after sealing simpler. The disadvantage of Kovar is that it is easy to change its crystal structure (austenite to martenite) and change its properties, such as increasing its resistivity. Therefore, Kovar parts must be annealed after such processing. Before sealing, Kovar parts must be annealed at about 1000 ℃ in wet hydrogen, which can not only relieve stress, but also decarburize the surface, so that Kovar parts will not have bubbles at the sealing place due to oxidation of surface carbon, which will reduce the strength of the sealing place and cause chronic gas leakage. In addition, due to the high resistivity of Kovar, if the problem of cracking caused by overheating is considered when it is used as lead wire, a layer of high conductivity material, such as gold, silver and copper, is usually plated on the Kovar surface, or large area contact is made. The composition proportion of Kovar is very important, otherwise it will affect the stress of sealing surface.A283M Grade D Carbon Steel Sheet
In electric vacuum devices, Fe Ni drill sealing alloy is widely used to make lead out ring, lead out wire, tube shell and other parts.schedule 40 sa179 seamless carbon steel tube for best price

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