Young's Modulus and Its Variation with Magnetization in Annealed Iron-Cobalt Alloys
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With annealed iron-cobalt alloys covering the whole composition range, Young's moduli and their changes with magnetization (the 〓E effect) in magnetic fields up to 900 Oe have been measured at ordinary temperatures using the method of magneto-strictively excited longitudinal vibration. In this connection, the density and some ferromagnetic properties have also been determined. It has been found that the negative 〓E effect occurs at weak magnetic fields in most alloys excluding 45〜50 and 100%Co. The absolute magnitude of the negative minimum of the 〓E effect is, at most, of the order of 0.1 % in alloys containing less than 45%Co, while it amounts to more than 2% in alloys containing 65〜70%Co. The maximum measured values of the 〓E effect, (〓E/E_0)_<max>, which are approximate to the saturation values, (〓E/E_0)_s excepting only for pure cobalt, are all positive in the whole composition range of the alloys. The (〓E/E_0)_<max> vs. composition curve exhibits a very sharp and high peak of 22.10% at about 50%Co. The trend of the curve in the α (body-centered cubic) phase range agrees qualitatively very well and quantitatively-fairly well with the results of calculation by a formula (〓E/E_0)_s=(0.7χ_0λ_s^2E_0/I_s^2)/(1-0.7χ_0λ_s^2E_0/I_s^2), where χ_0λ_s, I_s, and E_0 are the initial magnetic susceptibility, saturation magnetostriction, saturation magnetization, and Young's modulus at unmagnetized state, respectively. The Young's modulus at unmagnetized state vs. composition curve shows two maxima at about 25〜30 and 60%Co and one minimum at about 50%Co in the α phase range, and then falls considerably up to its boundary (at about 80%Co). The modulus recovers in the α+γ phase range, but it decreases again in the narrow ε (hexagonal close-packed) phase range. The marked discrepancies found between the results of the present dynamical measurements and those of the previous statical measurements by Honda and Tanaka on the 〓E effect and Young's modulus at unmagnetized state are shown to be due to differences in purity and in treatments of the specimens as well as to differences in the state of stress at the time of measurements of the specimens. It is also shown that, with an addition of cobalt to iron, the density increases approximately hyperbolically up to cobalt, except for a small discontinuity near 80%Co, and the initial magnetic susceptibility exhibits a sharp maximum near 50%Co and a flat minimum at 65〜75%Co.
- 東北大学の論文
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