Hybrid elevated-temperature, low/high-voltage plasma immersion ion implantation of AISI304 stainless steel

Elevated-temperature plasma immersion ion implantation (PIII) is an effecti ve non-line-of-sight technique to harden austenitic stainless steel by prod ucing expanded austenitic phases in the near surface region. We report here a hybrid elevated-temperature, low/high voltage approach, which improves t he efficiency while retaining the non-line-of-sight advantages of PIII. A l ow-voltage (4 kV), elevated-temperature (355 degreesC) pill process is firs t used to produce the modified layer, but the nitrogen concentration in thi s layer is typically relatively low and the thickness may not be adequate. This is followed by high-voltage (25 kV) PIII at a lower temperature to inc rease the nitrogen concentration and to achieve the desirable surface enhan cement effects. To assess the efficacy of the technique, the samples are ch aracterized using X-ray diffraction (XRD), nanohardness measurements, and s econdary ion mass spectrometry (SIMS) depth profiling. The experimental res ults show that the nitrogen concentration increases by nearly 75% and the n itrogen penetration depth nearly doubles that of the low-voltage sample. Th e surface microhardness also improves by 150% and our data suggest that it is due to the formation of expanded austenites. (C) 2001 Elsevier Science B .V. All rights reserved.