A Brief History of Permalloy
In 1913, the American scientist G.W. Elmen discovered that Ni-Fe alloys containing between 30% and 90% nickel exhibited excellent soft magnetic properties in weak and moderate magnetic fields. Among these alloys, the nickel-iron alloy with 78% nickel showed particularly high initial permeability μi; thus, it was named Permalloy, meaning "magnetic-permeable alloy." Elmen also developed a special heat-treatment process that further enhanced the initial permeability of 50% to 90% Ni-Fe alloys, a process known as "Permalloy heat treatment." In 1921, the 78% Ni-Fe alloy was first used in telephone relays. In 1924, British scientists led by Smith invented a 76% Ni-Fe alloy doped with copper and chromium, which came to be known as Mumetal (produced by the British company Telcon). In 1931, the American T.D. Yensen developed a process involving vacuum melting and high-temperature annealing in hydrogen gas to purify the alloy, leading to the creation of a super-nickel-iron alloy marketed under the brand name Hipernik. In 1934, the American G.A. Kelsall found that magnetic-field-assisted heat treatment could significantly improve the maximum permeability of iron-nickel alloys. After magnetic-field-assisted heat treatment, the 65% Ni-Fe alloy (65 Permalloy) saw its maximum permeability μmax increase by about tenfold. In 1947, American scientists including R.M. Bozorth developed alloys with exceptionally high initial permeability μi and maximum permeability μm, dubbed "Super Permalloys." In the early 1960s, the Chinese Academy of Iron and Steel Research invented a method using transverse magnetic-field treatment combined with the addition of an appropriate amount of oxygen, yielding a 65% Ni-Fe alloy (Chinese grade 1J66) with Br and Hc approaching zero and remarkably stable permeability. Starting in the 1970s, in response to the growing demands of high-frequency switching power supplies and magnetic recording technologies, high-nickel Ni-Fe alloys began incorporating various elements such as niobium, tantalum, vanadium, tungsten, titanium, silicon, and aluminum, resulting in alloys with high hardness, high resistivity, low losses, and exceptionally high permeability. These alloys have become among the most representative soft-magnetic materials, boasting diverse performance characteristics, wide variety, and broad applications.
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