T. W. Capehart

ESTIMATING THE EFFECTIVE MAGNETOSTRICTION OF A COMPOSITE: A SIMPLE MODEL

For a composite consisting of magnetostrictive particles dispersed in a nonmagnetostrictive matrix, a simple, approximate model for the effective magnetostriction, defined as the ratio of the magnetostriction of the composite to that of the magnetostrictive component, is described. The predictions of the model compare well with measurements on SmFe2-based composites having Al and Fe matrices.

MAGNETOSTRICTIVE SMFE2/METAL COMPOSITES

We have fabricated novel magnetostrictive composites consisting of SmFe2 embedded in an Fe or Al matrix which feature high magnetostriction and good mechanical strength. Hot pressed composites of 50% SmFe2/50% Fe or Al by volume have magnetostrictive strains parallel to the applied magnetic field, λ∥, between −280 and −440 ppm when consolidated at 610 (Fe) or 540 °C (Al). One unique feature of this work is the production of the magnetostrictive SmFe2 component by melt spinning; ribbon-based composites with Al combine significant magnetic coercivity, Hci=3 kOe, with high magnetostriction (λ∥=−280 ppm). Unlike their brittle SmFe2 parent materials, the composites are easily machinable.

Processing effects on the magnetostrictive and physical properties of SmFe2/metal composites

Hot pressed SmFe2/Fe and SmFe2/Al composites combine the large magnetostriction of SmFe2 with the mechanical robustness of the Fe or Al matrix. Here we report the dependence of the magnetostriction, density, and mechanical hardness on processing parameters, specifically on the SmFe2 volume fill fraction and the consolidation temperature. The magnetostriction increases monotonically with increasing SmFe2 content, but both the density and hardness decrease; low fill fraction composites are within 10% of theoretical density and have hardnesses of 40–85 Rockwell B, whereas hot pressed SmFe2 powder alone has high porosity (exceeding 30%) and is too soft to register on the Rockwell B hardness scale. The best combination of properties lies in the range of 40%–60% SmFe2. Similar competition between magnetostriction and physical properties is observed as a function of the temperature used to consolidate the samples. The magnetostriction falls slowly as the hot press temperature increases, probably as a result of c...

Magnetostrictive Sm1−xNdxFe2/Fe composites from melt-spun precursors

We have fabricated magnetostrictive composites containing Sm1−xNdxFe2 in an Fe matrix by hot pressing. The magnetostrictive component was prepared by heat treating melt-spun precursors, a method we find capable of producing the MgCu2-type phase for Nd concentrations as large as x=0.5. We report physical and magnetic properties of the rapidly solidified precursor materials, as well as the magnetostriction λ of Fe-based composites formed with them. The intrinsic coercivity Hci of the melt-spun ribbons decreases from 2.0 kOe for SmFe2 to 0.5 kOe for Sm0.5Nd0.5Fe2. As x increases from 0 to 0.5, λ of the composites decreases roughly linearly with x from 430 to 80 ppm.

Preparation and characterization of La2-xCexFe14B compounds

Abstract Pseudoternary La2-xCexFe14B compounds having the tetragonal Nd2Fe14B crystal structure have been prepared over the entire 0≤x≤2 composition range. With appropriate heat treatment schedules, samples which were single-phase or nearly so were obtained for x=0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, and 2. Lattice constants (a, c), Curie temperature (TC), and magnetization data are reported for each of these materials. We find that (i) a, c, and TC decrease linearly with Ce content x; (ii) the magnetization at 5 K is essentially independent of x; and (iii) there is no evidence of the occurence of Ce3+ over any range in x.

Synthesis and Characterization of Alkyl-Bridged Bicycloheptanes as Traction Fluids

The traction fluid is a critical component of a toroidal-continuously variable transmission (T-CVT). As the medium that transmits power through the toroids, the traction fluid needs to provide a high traction coefficient and retain low dynamic viscosity at cold temperatures; this is a challenging combination of properties. A comparison of a variety of fluids shows a broad correlation between the traction coefficient and the fluids low temperature viscosity, or pour point. This work investigated a series of novel compounds as traction fluids through chemical synthesis and the measurement of their relevant physical properties. Specifically, four new alkyl-bridged bicycloheptane fluids have been synthesized and refined to high purity. Their traction coefficients, measured with a ball-on-disc traction apparatus, are comparable to those of commercial fluids over the relevant range of temperature and pressure. Their dynamic viscosities at low temperature, however, are higher than the viscosity of commercial fluids and exceed the value of 3 × 10 4 cP at −40°C. These bridged bicycloheptanes also exhibit a correlation between their low-temperature viscosity and traction coefficient. The reasons for this correlation are discussed, and the effect of the molecular structure on viscosity and traction coefficient is investigated. This analysis finds semi-quantitative relationships between fluid properties and the molecules volume, stiffness, and ring structure.