The microwave-absorption properties and microstructures of Fe-Ni and Fe-NiCr 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 l and permittivity e), 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 < À10 dB) all depend on milling time and d. Introduction of Cr affected the RL of the powders, especially the minimum RL of À19.8 dB at 7.2 GHz for Fe-Ni-Cr powder milled for 90 h (compared with À22 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.

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