Dose rate and microstructure of nitrogen ion-implanted chromium steels

X-ray diffraction and optical microscopy were used to analyze the microstructure of the surface layer on chromium steels subjected to low-energy, high-current-density nitrogen ion implantation. It was demonstrated that the phases formed are controlled by dose rate and chemical composition of steels. In the case of steel containing a low chromium content, a decrease in the dose rate corresponds to a deeper modified layer. For chromium-rich steel, the dose rate did not influence the thickness of the modified layer, but a high dose rate induced more effective hardening of the surface and formation of nitrogen-rich phases. The model is presented to explain dose rate and chemical composition influence on the microstructure of the surface.