Abstract
IRON-nickel alloys, containing 35–90 per cent nickel, have permeabilities very much greater than that of iron. These alloys, called ‘permalloys', are especially useful commercially for transformers. The addition of one or more of the elements molybdenum, chromium and copper to permalloys has proved advantageous. ‘Mumetal', which contains usually 5 per cent copper, 2 per cent chromium, 75 per cent nickel and 18 per cent iron, is perhaps the best known of the permalloys. It is used in transformers suitable for high frequencies and is notable not only for its high initial permeability (between 10,000 and 30,000) and its high electrical resistivity (60 microhm, cm.) but also for the very simple heat treatment required in its preparation. O. L. Boothby and R. M. Bozorth have described recent developments in these high-nickel alloys for use at low inductions (J. Appl. Phys., 18, 173 ; 1947 ; see also Bozorth, R. M., Rev. Mod, Phys., 19, 38 ; 1947). The new material ‘Supermalloy' (su-perm'-al-loy), developed during the Second World War and already supplied in considerable quantities to the U.S. Navy, contains 5 per cent molybdenum and 79 per cent nickel, the remainder being mainly iron with a little manganese. The alloy is heat-treated, being maintained at 1,300° C. in pure dry hydrogen and then cooled from 600° C. to 300° C. at a critical rate. Whereas its electrical resistivity is about the same as for ‘Mumetal', its initial and maximum permeabilities are many times larger, 50,000–150,000 for the initial, and 600,000–1,200,000 for the maximum, permeabilities. ‘Supermalloy' can be produced in the form of very thin insulated tape, suitable for transformer cores, and it is claimed that the use of this new alloy in communication transformers permits a threefold increase in the range of frequencies transmitted, and a pulse duration three times that previously obtained.
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‘Supermalloy' : a New Magnetic Alloy. Nature 161, 554 (1948). https://doi.org/10.1038/161554a0
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DOI: https://doi.org/10.1038/161554a0
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