Investigation of the Absorption Properties of the Alloys Fe-Ni and Fe-Ni-Cr Prepared by Mechanical Alloying

The microwave-absorption properties and microstructures of Fe-Ni and Fe-Ni-Cr alloys prepared by mechanical alloying were investigated in the frequency range 2-18 GHz. Other properties were studied by scanning electron microscopy, x-ray diffractometry, vibrating sample magnetometry, and transmission line theory. Dependence of reflection loss (RL), electromagnetic properties (permeability mu and permittivity epsilon), magnetic and dielectric loss tangent, impedance matching, and absorber thickness (d) on milling time is discussed. The alloy powders had excellent microwave-absorption properties in the frequency range 7 to 14 GHz. The minimum RL, the frequency at which the RL is minimum, and the bandwidth (RL < -10 dB) all depend on milling time and d. Introduction of Cr affected the RL of the powders, especially the minimum RL of -19.8 dB at 7.2 GHz for Fe-Ni-Cr powder milled for 90 h (compared with -22 dB at 9.9 GHz for Fe-Ni powder milled for the same time), suggesting that the Fe-Ni-Cr alloy could be a promising candidate as a microwave-absorbing filler at low frequencies. This may help broaden the range of microwave-absorbing materials.