Plasma nitriding behavior of pure iron pre-treated with fine particle peening

In this study, the effect of a hybrid surface modification process; combination of fine particle peening (FPP) and plasma nitriding, on microstructure of pure iron was investigated. Surface microstructures of plasma nitrided specimens pre-treated with FPP were characterized by Optical microscopy, Scanning electron microscopy (SEM), Energy dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was clarified that the nitrided layer of the hybrid surface treated specimen was thicker than that of the nitrided one. This was because the fine grains created by FPP facilitated the nitrogen diffusion during the following nitriding process. However, no noticeable differences were observed in crystal structure of the compound layer between hybrid surface treated specimen and nitrided specimen. In order to change the crystal structure of the compound layer, FPP was performed using a chromium particle; has a strong affinity for nitrogen, prior to nitriding. The results showed that chromium nitride was generated on the treated surface during the nitriding. These results mean that the proposed hybrid surface modification process is possible to shorten the nitriding time and to change the structure of the compound layer.