Effect of Sputtered Fe on the Plasma Nitriding Mechanism of AISI H13 Tool Steel Using Electron-Beam-Excited Plasma

The effects of sputtered Fe on the formation of nitrided layers were clarified experimentally by controlling the potential of the sample and the Fe plate in electron-beam-excited plasma (EBEP). Plasma nitriding of AISI H13 tool steel was performed under bias voltages ranging from +3 to −300 V applied to a pure Fe plate installed separately from the samples and plasma generation electrode. The results showed that the plasma density, plasma potential, and N species around the sample did not change when the bias voltage of the Fe plate was varied. The results clarified that the sputtered Fe deposited as a α-Fe or γ′-Fe4N onto the sample surface during nitriding. The depth of the nitrided layer was the same under experimental conditions where sputtering did not occur. The effect of sputtering increased as the negative bias voltage VFe was increased; when the VFe was −300 V, the effect of sputtering on the formation of the nitrided layer was ~34% of the total. The diffusion layer on the surface was formed by neutral species when the plasma nitriding was performed at a VFe of −50 or +3 V. When the Fe plate potential was less than −80 V, FexN could be deposited onto the sample surface. Therefore, FexN in addition to neutral species were present on the sample surface among the species that induced a nitriding effect. The depth of the nitrided layers was greater than that of plasma-nitrided layers formed only by neutral species.