| The influence of pulsed-dc plasma oxidation and nitriding treatment on the surface microstructure with variation of duty factors of cast iron is studied. The phase compositions of the layers were evaluated by using X-ray diffraction. OES(Optical Emission Spectroscopy) have been applied to analyse the active species during plasma oxidation. Surface properties of plasma oxidation and nitriding treated specimens were summarized. Oxide composition was not changed with duty factor (0.1∼0.9, pulse on-off time : 100∼900 ㎲, pulse frequency 1,000 Hz), but the retained α-Fe reduced significantly with increasing duty factor. The intensity ratio of oxygen plasma spectra shows that the formation density of oxygen radical reached maximum at duty factor of 0.5 and etching depth was 1,840 ㎚ under that condition. |
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