Coercive force and saturation induction of cobalt, iron, and nickel, dispersion strengthened with 0.02 to 0.10 volume fraction of alumina or thoria, were measured at temperatures up to 80%–98% of TC. Saturation magnetization values of iron and cobalt at a given temperature level were found to decrease in direct proportion to the volume fraction of nonmagnetic phase present. The temperature dependence of the measured coercive force was interpreted as a cooperative effect of inclusions and internal stress by reference to coercive force values calculated from the equations of Néel. This was particularly apparent in the Hc vs T curve of nickel where the contribution of inclusions was significant in the low-temperature region, whereas stress was an influential factor at all temperatures. Close correlation between measured and calculated Hc was obtained for all three metals containing 0.02–0.025 volume fraction of dispersoid.

The need for soft magnetic materials to operate at high temperatures in space electric-power systems requires a more fundamental understanding of the effects of nonmagnetic phases on basic magnetic behavior of synthetically strengthened metals. Coercive force (Hc) was measured at room temperature and 1200°F (649°C)–1600°F (871°C) on nineteen Co-base and ten Fe +27% Co-base extrusions dispersion-strengthened with 0.02–0.3 volume fraction (V) of oxide and boride particles ranging from 0.1 to 1.6 micron average diameter (d). The measured effect of this range of dispersoid parameters on Hc was correlated and interpreted by reference to equations of the form developed by Kersten, Néel, and Mager for particular inclusion sizes. The increase in Hc with V/d ratio was linear in most instances. Small changes in Hc resulted from the development of a fibrous subgrain structure by secondary working treatments (cycles of swaging and partial stress-relief annealing). These treatments provided both a substantial strengthening effect and thermal stabilization of the matrix for those materials containing finer dispersions, V/d≧0.75. Conclusions were reached concerning the limits of application and refinement of theoretical equations for predicting the influence of dispersoids and temperature on Hc.

Different types of composite materials containing dispersoids, fibers, or aligned-eutectic structure in a matrix of either cobalt or iron or their alloys were investigated for potential use as solid-rotor core materials operating at 1200 to 1600 F under stress. Composite-strengthening methods deteriorated the soft-magnetic quality of the matrix material. Magnetic saturation induction (Bs) decreased in direct proportion to the volume fraction of nonmagnetic phase present. In regard to structure-sensitive magnetic properties, such as coercive force (Hc) and d-c magnetization curve, the effects of matrix composition, amount and distribution of secondary phase, internal stress, demagnetization effects, and temperature were studied experimentally and interpreted by reference to theory. The overall consideration of both magnetic and mechanical performance, as well as ease of processing and thermal stability, favored dispersion-strengthened iron + 27 weight percent cobalt-base material for further development.

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