Coercive force and microstructure in a Zr-permalloy |
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Authors: | C R Frohlich G Krauss J L Bestel |
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Affiliation: | (1) Western Electric Co., Inc., Baltimore, Maryland;(2) Lehigh University, 18015 Bethlehem, Pa.;(3) Western Electric Co., Inc., Princeton, New Jersey |
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Abstract: | An alloy containing 80.0 pct Ni, 12.65 pct Fe, 6.74 pct Mo, 0.36 pct Zr, and 0.25 pct Mn by weight was cast, homogenized,
and successively cold rolled into thin strips with area reductions of 0, 50, 75, and 90 pct. Annealed samples were studied
by optical and electron microscopy, electron diffraction, and magnetic testing to determine the effects of cold work and annealing
upon the microstructure and magnetic properties of the alloy. Cold work produced a high initial hardness together with high
coercive force. Recrystallization of the cold worked structures occurred upon annealing at 600°C (873 K) and above and caused
significant and parallel decreases in hardness and coercive force. The activation energy for recrystallization was found to
be 80.5 kcal/g mole (337.0 kJ/g mole) for the 50, 75, and 90 pct cold worked specimens. After annealing at 600°C (873 K),
a small number of spherical Ni4Mo particles were observed, but the particles produced little change in magnetic properties apparently because of their relatively
coarse size and large spacing. Beginning at 700°C (973 K) ribbon-shaped particles of a Ni5Zr intermetallic compound also precipitated out of solid solution. Both the Ni4Mo and Ni5Zr precipitates were the result of a homogeneous continuous precipitation reaction within the grains. A peak in coercive force
at 800°C (1073 K) is attributed to domain wall pinning associated with the fine distribution of rodlike Ni5Zr particles. Cold working 90 pct and aging at 800°C (1073 K) was found to increase coercive force by almost 60 pct from the
minimum produced by complete recrystallization. Annealing, however, decreased hysteresis and improved squareness. |
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