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This paper presents a study of microstructural changes induced in CrN layers by irradiation with 120 keV argon ions. The layers were deposited on (100) Si wafers, at different nitrogen partial pressures (2×10^-4, 3.5×10^-4 and 5×10^-4 mbar), to a total thickness of 260–280 nm. During deposition the substrates were held at 150°C. After deposition the samples were irradiated with argon ions to the fluences of 1×10^15 and 1×10^16 ions/cm2, under the vacuum of 7×10^-6 mbar. Characterisation of the samples structure and morphology were performed by X-ray diffraction (XRD) analysis and cross-sectional transmission electron microscopy (XTEM), and the concentration profiles were determined by Rutheford backscattering (RBS) spectrometry. It was found that the layer composition strongly depends on the nitrogen partial pressure during deposition. A pure stoichiometric CrN phase was achieved for the highest nitrogen partial pressure (5×10^-4 mbar). Argon ions irradiation induces microstructural changes in the CrN layers such as variation of the lattice constants, micro-strain and mean grain size.