Modification of the microstructure and properties of martensitic steel during ultra-high dose high-intensity implantation of nitrogen ions

Abstract In this work, we report a study of the chemical and phase composition, structural modifications and mechanical properties of martensitic stainless steel surface layers modified by high-intensity nitrogen ion implantation using a high current beam of low-energy nitrogen ions. The effect of ultrahigh-dose implantation of nitrogen ions into steel using a high-intensity repetitively pulsed beam of nitrogen ions with a current of 0.6 A (at an ion energy of 1.2 keV) and a sample temperature of 500 °C is investigated. The fluence of ion irradiation in the range from 6 × 1021 ions/cm2 to 2.25 × 1021 ions/cm2 varied by changing the current density and implantation time. The studies performed using transmission electron microscopy and X-Ray diffraction analysis of the microstructure and phase composition of the implanted samples showed that the surface-doped layer formed up to 75 μm thick and contains ferrite, iron nitride Fe4N, and chromium nitride CrN (α-phase – 70.88 vol.%, γ'-Fe4N – 16.30 vol.%, CrN – 12.82 vol.%). The obtained values of the coherent scattering region size of the formed chromium nitride and iron nitride indicate a very high dispersion of the elements in the ion-doped layer substructure. The data on changes in the surface morphology and microhardness of the near-surface layers are presented.