The relations of internal friction
Q−1 with coercive force
Hc, hysteresis loss
Wh and magnetostriction λ for Fe-Mo alloys were studied by varying the heating temperature and cooling rate. Measurement of
Q−1 was carried out by the inverted torsion pendulum method at a maximum shear strain amplitude of 1∼270×10
−6 at a frequency of about 1 Hz. Both
Hc and
Wh were measured using the automatic recording fluxmeter, and λ by the optical roller method.
The
Q−1 value of Fe-Mo alloys became higher with increasing heating temperature. For the alloys with 0∼2%Mo, the
Q−1 value was generally low, and in the furnace-cooled state
Q−1 was higher than that in the rapidly cooled state. By contrast, for the alloys with 4∼8%Mo,
Q−1 was generally high and showed a slight variation with cooling rate. Among the alloys the Fe-6%Mo alloy showed a maximum value of
Q−1. For the alloys with 10∼16%Mo,
Q−1 became higher by rapid cooling from high temperatures, suggesting that the precipitation of the non-ferromagnetic β phase in the matrix of ferromagnetic α phase was substantially reduced by quenching.
The
Hc value of the alloys with high
Q−1 value was as small as about 0.05 kA/m, and consequently the magnetic rearrangement was readily caused by a small amplitude of strain when the vibrational stress applied. The
Q−1 values of all the Fe-Mo alloys decrease with increasing magnetic field
H. Further, the values of
dWh⁄
dH and
dλ⁄
dH, which are the slopes of the lines which connect the origin and each point on the
Wh and λ vs
Hc urves respectively, increase gradually with
H, and then decrease after attaining the maxima. The strength of
H for the most remarkable decrease in
Q−1 with
H is almost consistent with those for the maximum values of
dWh⁄
dH and
dλ⁄
dH. These gradients in weak magnetic fields are in proportion to the values of
Q−1. The results indicate that the high damping capacity of Fe-Mo alloys is due largely to irreversible magnetization, and then is casued by the resultant large magnetic energy loss per cycle when the small vibrational energy applied.
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