Low-energy high-flux nitriding of Ni and Ni20Cr substrates

The influence of a low-energy high-flux nitrogen implantation on the structure and hardness of Ni and NiCr20 is examined. These implantation–diffusion experiments carried out at 475 and 450 °C, respectively, show that the nitriding process is very difficult for the pure Ni metal, whereas in the NiCr20 substrate the formation of an expanded austenite γN phase is identified by X-ray diffraction. Vickers microhardness indentation tests indicate an important hardening effect of the NiCr20 substrate surface. The absence of any detectable nitridation effect in pure nickel substrates can be correlated with the low solubility of nitrogen. An increase in surface roughness and the presence of porosity is nevertheless observed by scanning electron microscopy and atomic force microscopy on both metallic substrates surfaces after the implantation process. This behaviour can be correlated with the sputtering effect produced by the very high implantation dose.