因瓦合金纳米微粉的恒磁导率及其压力、频率特性和压力相变

 以Fe-30wt%Ni合金片为母合金，用蒸发冷凝法制备了三种粗细不同的纳米微粒。经透射电镜和X光衍射物相分析，微粒成分与母合金一致。5T、5H和3K粉的平均粒度分别为13.6、27和40 mm。在室温和43~28个不同的流体静压力（0.000 1~2.205 GPa）下测量了它们的磁化曲线、磁导率曲线和起始磁化曲线。结果表明：（1）在H＝(20－132)(1000/4π)A/m范围内Fe-30Ni合金三种纳米粉均具有恒磁导率。（2）三种纳米粉恒磁导率随静水压的变化规律如下：μ_r＝3.83+0.253p-0.022 1p²-0.007 22p³（5T粉）；μ_r＝3.93+1.20p-1.97p²+1.52p³-0.510p⁴+0.059 9p⁵（5H粉）；μ_r＝5.96-0.276p+0.107p²-0.045 9p³（3K粉）。前两者随压力增加而升高。后者随压力增加而下降。（3）γ-α马氏体相变明显存在于5T、5H粉中，而3K粉中未见到。（4）Fe-30Ni合金片的μ_i从200kHz至2 MHz已下降一个数量级，而其纳米粉μ_i的频率范围高于300 MHz，增大两个数量级以上。

γ-α Phase Transition under Pressure, Constant Magnetic Permeability and Its Pressure as Well as Frequency Characteristic in Nanometer-Scale Powder of Invar Alloy

By means of evaporation and condensation, three kinds of nanometer-scale powder of invar alloy (Fe-30wt%Ni) were prepared. It is found out with the method of TEM and X-ray diffraction that their composition coincides with its matrix alloy, average grain size is 13.6 nm (powder 5T) and 27 nm (powder 5H) and 40 nm (powder 3K). Under room temperature and hydrostatic pressure of 43~28 different magnitudes ranging from 0.000 1 to 2.205 GPa, the magnetization curve and initial magnetization curve were measured to see their relation with pressure. The authors point out: (1) the three kinds of nanometer-scale powder of invar alloy (Fe-30wt%Ni) all possess constant magnetic permeability when H＝(20－132)(1000/4π)A/m; (2) constant magnetic permeability, μ_r varies with the pressure as follows: μ_r＝3.83+0.253p-0.022 1p²-0.007 22p³, μ_r＝3.93+1.20p-1.97p²+1.52p³-0.510p⁴+0.059 9p⁵, μ_r＝5.96-0.276p+0.107p²-0.045 9p³ , μ_r of powder 5T and 5H rises, but μ_r of powder 3K decreases when pressure increases; (3) γ-α Martensite phase transition under high pressure exists obviously in ultramicron 5H and 5T, but not in ultramicron 3K; (4) μ_i of Fe-30wt%Ni alloy piece decreases in one order of magnitude in the frequency range from 200 kHz to 2 MHz, but when frequency range for their ultramicrons is over 30 MHz, the value of μ_i does not decrease greatly so its frequency range extents two orders of magnitude as compared with its piece.