Surface modification of metal alloys by plasma immersion ion implantation and subsequent plasma nitriding

Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersion ion implantation (PIII) is a newly developed technology, which provides ion implantation at moderate energy (10–50 keV), and thereby allowing penetration depths deeper than the surface oxide barrier. The damage caused by ion implantation together with the surface sputtering may create favorable boundary conditions for an efficient subsequent diffusive treatment such as nitriding. Surface modification of aluminum alloy 5052, Ti6Al4V alloy and steels (AISI 304 and H13) by a combination of PIII and plasma nitriding (PN) has been investigated. Nitrogen ions were implanted into specimens at 15 kV and then ion nitrided at low pressure with bias of −800 V. Compared to the untreated samples the hardness of Ti6Al4V alloy and AISI 304 steel could be improved significantly. The hardness of H13 steel can be increased by 20% using a duplex process with 4-h nitriding time. X-ray diffraction (XRD) results have shown some structural modification of the metallic samples and formation of a double-layer structure in AISI 304, treated by PIII and PN. Nitrogen depth profile of the same stainless steel sample, obtained by Auger electron spectroscopy (AES), shows two rather well-defined nitrogen enriched regions with different N contents: high (25–30 at.%) in a surface layer and medium (∼10%) in a subsurface layer.