Recent experiments on plasma immersion ion implantation (and deposition) using discharges inside metal tubes

Plasma immersion ion implantation (PIII) of nitrogen inside metallic tubes of different diameters and configurations were attempted recently. PIII tests in practical size metallic tubes of SS304, ranging from 1.1 to 16 cm∅ and length of 20 cm, were carried out as a continued effort in our lab, to explore PIII inside tubes. Tubes in laying down positions and configurations including metallic lid in one side or both sides open were used, as well as, plane sample support placed 10 cm far from the tube mouth and without bias, taking advantage of plasma flowing out the tube. In particular, nitrogen and argon PIIIs were tested for tube inner wall sputtering and deposition studies, running the PIII system in the last configuration of sample support detached from the tube. During the nitrogen ion implantation runs in other cases, it was found that the final temperature of the tubes and the plasma turn-on voltages were both inversely proportional to the dimensions of the tubes, except for the smallest tube tested. High voltage glow and hollow cathode discharges were produced inside the tubes, either alternately, during the pulse or independently, depending on the tube geometry and pulser used (LIITS, a current controlled source or RUP-4, a voltage controlled one). In the case of smallest diameter of 1.1 cm∅, a suspended tube of SS304 was tested using lower power pulser (RUP-4), at its near maximum capability of 1.2 kW. In this case also, very bright plasmas were formed, mainly inside the tube and resulted in high temperature there (~700 °C). Nitrogen uptake was superior for higher temperature PIII treatments (>700 °C), combining ion implantation and thermal diffusion, which allowed the formation of TiN and Ti2N on the Ti alloy samples inside tubes with diameters ≤4 cm. In this paper, detailed discussion of results of above cited PIII tests with diversified tubes and configurations are presented, together with the analysis of the corresponding treated surfaces of the samples inside, outside and on the support detached from the tube.