Low-temperature nitriding of stainless steel in an electron beam generated plasma

An electron beam generated plasma processing system was characterized with in situ diagnostics and employed for a series of low energy (350 eV) stainless steel nitriding experiments in the temperature range of 325–462 °C. Plasma characterization yielded quantitative ion specie fluxes to the stainless steel workpiece in an argon–nitrogen plasma, with a significant fraction of the flux comprised of N+ ions. The nitriding rates were as high as 20 μm h−1/2 with surface layers exhibiting hardness values of approximately 15.5 GPa for specimens processed at all temperatures. X-ray diffraction analysis revealed nitrogen concentrations of approximately 30 at.% in all samples processed below 460 °C. The process activation energy was comparable to that in nitriding systems with higher ion fluxes, suggesting favorable plasma chemistry with respect to plasma nitriding applications.