Effect of carbon on interstitial ordering and magnetic properties of ε-Fe2(N,C)_1-z

Hexagonal ε-iron nitride and ε-iron carbonitride phases are formed on nitriding and nitrocarburizing ofiron and steel surfaces and can exist in broad compositional ranges. Long-range nitrogen ordering andmagnetic properties for ε-iron nitrides and their dependence on composition have been the focus of several studies.

So far, limited attention has been paid to the carbonitrides. In the current work, the effects of substitution of nitrogen by carbon on the interstitial ordering and magnetic properties in Fe2(C,N)1-z are explored using neutron diffraction, M€ossbauer spectroscopy and vibrating samplemagnetometry. Neutron diffraction patterns showed 001 and 301 superstructure reflections, confirminga previously proposed structural model in space group P31m (compared to P6322 for the pure nitrides).On partial substitution of nitrogen by carbon in ε-iron nitride the Curie temperature, the saturationmagnetization and the hyperfine fields of the iron atoms are increased, while isomer shifts are decreased.The effects on the a and c lattice parameters indicate a change in interstitial ordering, which is related tomore favorable interactions between a nitrogen and carbon atom than among nitrogen atoms.

Thisinteraction leads to additional interstitial (short-range) ordering and a decrease in the c lattice parameter,while the a lattice parameter is largely unaffected.