Controlled Expansion Alloys

Controlled expansion alloys are also called expansion alloys or thermal expansion alloys, which are precision alloys with abnormal thermal expansion characteristics. Widely used in electronic industry, precision measuring tools, precision instruments and low temperature engineering and other fields.

General metals and alloys expand when heated, and the amount of expansion increases linearly with the increase of temperature, but the thermal expansion curve of some alloys has a bending point at a certain temperature, and the thermal expansion coefficient below the bending point is lower than the normal thermal expansion coefficient above the bending point. Much more, this phenomenon is called anomalous thermal expansion characteristics.

Expansion alloys are divided into low expansion alloys and constant expansion alloys, the latter also known as sealing alloys (glass sealing alloys). The average expansion coefficient of the low-expansion alloy below the inflection point is lower than 3×10-6℃-1; the average expansion coefficient of the constant expansion alloy below the inflection point is about (4～10)×10-6℃-1.

Expansion alloys mainly include Fe-Ni series, Fe-Ni-Co series and Fe-Ni-Cr series alloys, etc. High chromium steel and Co-Fe-Cr series alloys are also used as expansion alloys, but the amount is not large.

In addition to a specific thermal expansion coefficient, the expansion alloy also requires good sealing, weldability, corrosion resistance, machinability and ease of machinability according to different uses, and it is not allowed to cause expansion within the operating temperature range. A distinct phase transition. The chemical composition of the expanded alloy must be accurately controlled during the manufacturing process, and its products are generally rods, plates, strips, wires and tubes.

The main grades of control expansion alloys are as follows :

Kovar Alloy and equivalent grade

Super Invar 32-5 and equivalent grade

Invar 36 and equivalent grade

4J33 alloy and equivalent grade

4J34 alloy and equivalent grade

Vacovit 500 and equivalent grade

4J80 alloy and equivalent grade

4J45 alloy and equivalent grade

Nilo42 and equivalent grade

4J28 and equivalent grade