Permalloy, applications

Contains levels of nickel which vary widely in content. Commercial products include Invar and Permalloy. These alloys are used in certain high-level technology applications such as transoceanic cabling and other applications whereby machining tolerances are exact, such as clocks and variable condensers. 

Magnetically soft Fe-Ni alloys can have their properties altered by heat treatment. The compound NisFe undergoes an order-disorder transformation at about 500°C. Since the susceptibility of the ordered phase is only about half that of the disordered phase, a higher susceptibility is realized when the alloy is quenched from 600°C, a process that retains the high-temperature, disordered structure. Heat treatment of Fe-Ni alloys in a magnetic field further enhances their magnetic characteristics (see Figure 6.61), and the square hysteresis loop of 65 Permalloy so processed is desirable in many applications. A related alloy called Supermalloy (see Table 6.19) can have an initial susceptibility of approximately one million. 

Only about 10 elements, ie, Cr, Ni, Zn, Sn, In, Ag, Cd, Au, Pb, and Rh, are commercially deposited from aqueous solutions, though alloy deposition such as Cu—Zn (brass), Cu—Sn (bronze), Pb—Sn (solder), Au—Co, Sn—Ni, and Ni—Fe (permalloy) raise this number somewhat. In addition, 10—15 other elements are electrodeposited in small-scale specialty applications. Typically, electrodeposited materials are crystalline, but amorphous metal alloys may also be deposited. One such amorphous alloy is Ni—Cr—P. In some cases, chemical compounds can be electrodeposited at the cathode. For example, black chrome and black molybdenum electrodeposits, both metal oxide particles in a metallic matrix, are used for decorative purposes and as selective solar thermal absorbers (19). 

The deposition of Fe-Ni alloys is of industrial interest because these materials find applications in electronic devices (e.g. PC hard disk). The most popular alloys are Permalloy (soft magnetic properties) and Invar (veiy low thermal expansion). The magnetic and mechanical properties of Fe-Ni alloy can be designed by nanostructuring. Natter and Hempelmann (2003) used an electrolyte containing 40g/l NiS04, 20g/l (NH lCl, 20g/l Na citrate, 5g/l citric acid, lg/1 saccharin, 45 g/1 boric acid and a variable content of iron (II) ammonium sulfate. The pulse parameters used were t 2 ms, 48 ms and 250mA/cm2. For different concentrations of iron salts, alloys (crystallite size, 16-19 nm) with iron content between 0 and 71 mol% conld be obtained. 

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