- 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)(1000/4)A/m; (2) constant magnetic permeability, r varies with the pressure as follows: r＝3.83+0.253p-0.022 1p2-0.007 22p3, r＝3.93+1.20p-1.97p2+1.52p3-0.510p4+0.059 9p5, r＝5.96-0.276p+0.107p2-0.045 9p3 , r of powder 5T and 5H rises, but r of powder 3K decreases when pressure increases; (3) - Martensite phase transition under high pressure exists obviously in ultramicron 5H and 5T, but not in ultramicron 3K; (4) 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 i does not decrease greatly so its frequency range extents two orders of magnitude as compared with its piece.