Low vacuum MEVVA titanium and nitrogen co-ion implantation into D2 steel substrates

Co-implantation of titanium and nitrogen into D2 steel was conducted using a conventional metal vapor vacuum arc (MEVVA) ion source under low vacuum. Nitrogen was introduced into the vacuum chamber to decrease the mean free path of the particles below the distance between the ion source and targets. The experimental results show that when the pressure goes up from 5×10−3 to 5×10−2 Pa by bleeding in nitrogen, the ion beam current density decreases by 30% and the surface hardness of the implanted specimen increases from 760 to 950 HV. Our results suggest that the optimal nitrogen pressure and implantation dose are 3.5×10−2 Pa and 3.5×1017 ions/cm2, respectively. Depth profiles acquired by Auger electron spectroscopy (AES) reveal that the implantation depth is approximately 600 nm but the profiles do no resemble a Gaussian distribution. Instead, a surface plateau can be seen. Analyses of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) indicate that metal nitrides form in the surface layer and the nitrogen concentration in the surface layer is as high as 13.4 at.%.