Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. λ 100 exhibits two peaks as a function of Ga content. At room temperature, λ 100 reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, λ 100 drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling |b 1 | of Fe with increasing amounts of nonmagnetic Ga, combined with a strongly temperature dependent elastic shear modulus (c 11 −c 12 ) which approaches zero near 27% Ga. λ 111 is significantly smaller in magnitude than λ 100 over this composition range, and has an abrupt change in sign from negative for low Ga concentrations to positive for a concentration of Ga near 21%. Extraordinary magnetostrictive behavior has been observed in Fe-Ga alloys with concentrations of Ga between 4% and 27%. 100 exhibits two peaks as a function of Ga content. At room temperature, 100 reaches a maximum of 265 ppm near 19% Ga and 235 ppm near 27% Ga. For compositions between 19% and 27%, 100 drops sharply to a minimum near 24% Ga and exhibits an anomalous temperature dependence, decreasing by as much as a factor of 2 at low temperatures. This unusual magnetostrictive behavior is interpreted on the basis of a single maximum in the magnetoelastic coupling ͉b 1 ͉ of Fe with increasing amounts of nonmagnetic Ga, combined with a strongly temperature dependent elastic shear modulus (c 11 Ϫc 12 ) which approaches zero near 27% Ga. 111 is significantly smaller in magnitude than 100 over this composition range, and has an abrupt change in sign from negative for low Ga concentrations to positive for a concentration of Ga near 21%.
Iron-based amorphous metals are investigated as nonferromagnetic amorphous steel alloys with magnetic transition temperatures well below ambient temperatures. Rod-shaped amorphous samples with diameters reaching 4 mm are obtained using injection casting. Amorphous steel alloys are designed by considering atomistic factors that enhance the stability of the amorphous phase, coupled with the realization of low-lying liquidus temperatures. The present alloys are found to exhibit superior mechanical strengths. In particular, the elastic moduli are comparable to those reported for super austenitic steels.
This paper presents a comparative study on the tetragonal magnetostriction constant,λ γ,2 , [ = (3/2)λ 100 ] and magnetoelastic coupling, b 1 , of binary Fe 100-xZ x (0 < x < 35, Z = Al, Ga, Ge, and Si) and ternary Fe-Ga-Al and Fe-Ga-Ge alloys. The quantities are corrected for magnetostrains due to sample geometry (the magnetostrictive form effect). Recently published elastic constant data along with magnetization measurements at both room temperature and 77 K make these corrections possible. The form effect correction lowers the magnetostriction by ∼10 ppm for high-modulus alloys and by as much as 30 ppm for low-modulus alloys. The elastic constants are also used to determine the values of the magnetoelastic coupling constant, b 1 . With the new magnetostriction data on the Fe-Al-Ga alloy, it is possible to show how the double peak magnetostriction feature of the binary Fe-Ga alloy flows into the single peak binary Fe-Al alloy. The corrected magnetostriction and magnetoelastic coupling data for the various alloys are also compared using the electron-per-atom ratio, e/a, as the common variable. The Hume-Rothery rules link thee/a ratio to the regions of phase stability, which appear to be intimately related to the magnetostriction versus the solute concentration curve in these alloys. Using e/a as the abscissa tends to align the peaks in the magnetostriction and magnetoelastic coupling for the Fe-Ga, Fe-Ge, Fe-Al, Fe-Ga-Al, and Fe-Ga-Ge alloys, but not for the Fe-Si alloys for which the larger atomic size difference may play a greater role in phase stabilization. Corrections for the form effect are also presented for the rhombohedral magnetostriction,λ ɛ,2 , and the magnetoelastic coupling, b 2 , of Fe 100-x Ga x (0 < x < 35) alloys.Keywords aluminium alloys, elastic constants, elastic moduli, gallium alloys, germanium alloys, iron alloys, magnetisation, magnetoelastic effects, magnetostriction, silicon alloys Disciplines Condensed Matter Physics | Metallurgy CommentsThe following article is from Journal of Applied Physics 111 (2012) This paper presents a comparative study on the tetragonal magnetostriction constant, k c,2 , [ ¼ (3/2) k 100 ] and magnetoelastic coupling, b 1 , of binary Fe 100-x Z x (0 < x < 35, Z ¼ Al, Ga, Ge, and Si) and ternary Fe-Ga-Al and Fe-Ga-Ge alloys. The quantities are corrected for magnetostrains due to sample geometry (the magnetostrictive form effect). Recently published elastic constant data along with magnetization measurements at both room temperature and 77 K make these corrections possible. The form effect correction lowers the magnetostriction by $10 ppm for high-modulus alloys and by as much as 30 ppm for low-modulus alloys. The elastic constants are also used to determine the values of the magnetoelastic coupling constant, b 1 . With the new magnetostriction data on the Fe-Al-Ga alloy, it is possible to show how the double peak magnetostriction feature of the binary Fe-Ga alloy flows into the single peak binary Fe-Al alloy. The corrected magnetostriction and magnetoel...
A group delay measurement technique is proposed using modally selective Lamb wave transducers for the detection and sizing of delaminations in unidirectional and cross-ply composites. Unlike amplitude or energy based Lamb wave methods, this method is insensitive to transducer coupling. Specifically, modally selective array transducers are used to generate the lowest antisymmetric A 0 Lamb mode in a zone with minimal dispersion. The change in the modal group velocity is used as a damage indicator while the accumulated time delay of the traveling ultrasonic wavepacket is used for size estimation of the delaminations. The results are repeatable and consistent, suggesting time delay as a reliable damage parameter for quantitative monitoring of delaminations and impact damage in composites.
Elastic shear moduli measurements on Fe100−xGax (x=12–33) single crystals (via resonant ultrasound spectroscopy) with and without a magnetic field and within 4–300 K are reported. The pronounced softening of the tetragonal shear modulus c′ is concluded to be, based on magnetoelastic coupling, the cause of the second peak in the tetragonal magnetostriction constant λ100 near x=28. Exceedingly high ΔE effects (∼25%), combined with the extreme softness in c′ (c′<10GPa), suggest structural changes take place, yet, gradual in nature, as the moduli show a smooth dependence on Ga concentration, temperature, and magnetic field. Shear anisotropy (c44∕c′) as high as 14.7 was observed for Fe71.2Ga28.8.
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