Super Invar

Low Expansion Alloys. Binary Fe—Ni alloys as well as several alloys of the type Fe—Ni—X, where X = Cr or Co, are utilized for their low thermal expansion coefficients over a limited temperature range. Other elements also may be added to provide altered mechanical or physical properties. Common trade names include Invar (64%Fe—36%Ni), F.linvar (52%Fe—36%Ni—12%Cr) and super Invar (63%Fe—32%Ni—5%Co). These alloys, which have many commercial appHcations, are typically used at low (25—500°C) temperatures. Exceptions are automotive pistons and components of gas turbines. These alloys are useful to about 650°C while retaining low coefficients of thermal expansion. Alloys 903, 907, and 909, based on 42%Fe—38%Ni—13%Co and having varying amounts of niobium, titanium, and aluminum, are examples of such alloys (2). 

Fig. 4.3-40 Thermal expansion curves of super invar alloys [3.17]...

Other low-expansion alloys have been developed. One of these is called Super Invar because its thermal expansion coefficient [0.72 X 10 (°C) ] is lower than the value for Invar. However, the temperature range over which its low expansion characteristics persist is relatively narrow. Compositionally, for Super Invar some of the nickel in Invar is replaced by another ferromagnetic metal, cobalt Super Invar contains 63 wt% Fe, 32 wt% Ni, and 5 wt% Co. 

D. G. Rancoutt, H. H. A. Smith, and R. C. Thiel, Metastable compositionally and magnetically modulated state of Fe-Ni Invar and the associated super-mon nt dynamics from Mossbauer spectroscopy, J. Magn. Magn. Mat, 66 121 (1987). 

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