High temperature plasma immersion ion implantation using hollow cathode discharges in small diameter metal tubes

High temperature nitrogen plasma immersion ion implantation (HT-NPIII) method was used to treat the internal walls of small diameter metal tubes made of SS304 and of Ti6-Al4-V (TAV). Using a lid in one side of the tubes was essential to reach high temperatures of 700-900 °C, necessary for high thermal diffusion of nitrogen in Ti alloy samples placed inside the metal tubes for monitoring the HT-NPIII process. The used metal tubes also reached such high temperatures. New phases of TiN and Ti2N were successfully attained in the TAV samples with the treated layer thickness of more than 1.3 μm for all the tested cases. For tubes made of SS304, HT-NPIII treatments resulted in redeposition of FeN thick layers with high hardness on the surfaces of the internal walls of the tubes and on the monitoring samples. Obtaining such HT-NPIII conditions in these small metallic tubes was possible by achieving high plasma density through hollow cathode discharges inside those tubes. These results were compared to the ones obtained on the nitrogen implantation treatments of TAV samples in moderate to high temperatures carried out previously in the laboratory which indicated the superior performance of the presently reported method of surface modification.