MAGNETIC-PROPERTIES AND MICROSTRUCTURE OF FE4N AND (FE,NI)4N

Single-phase Fe4N and (Fe1-xNix)4N compounds have been synthesized in a continuous form by heat treating iron and iron-nickel alloy sheets at various temperatures under NH3/H-2 atmospheres. The Fe4N sheet has a high room-temperature magnetization value of 179 emu/g (2.14-mu-B/Fe), which is only slightly less than 218 emu/g (2.19-mu-B/Fe) observed in pure iron. The magnetic moments of the Fe-Ni alloy nitrides decreased monotonically as x was increased, in contrast to those for the starting alloys Fe1-xNix which exhibited a peak value around x = 0.05. The decrease in magnetic moment with nickel content in the alloy nitrides was close to the value anticipated by magnetic dilution from nickel. The coercive force is about 5 Oe and is slightly decreased by the Ni substitution. The Fe-nitride offers a significantly improved corrosion resistance over pure iron. Even further improvement is obtained in the (Fe1-xNix)4N system with only slight sacrifice in magnetic moment. The addition of nickel has been found to noticeably improve the mechanical ductility of the normally brittle Fe4N compound. Theses nitrides also exhibit significantly increased electrical resistivity and wear resistance, and may be useful for a variety of technological applications.