Effects of Nickel Screen on Active Screen Plasma Nitriding

Abstract

Active screen plasma nitriding (ASPN) is a nitriding method that avoids the edge effects and arcing that occur during conventional direct current plasma nitriding (DCPN). Furthermore, applying voltage to a sample during ASPN allows the nitriding rate to be increased (S-DCPN). While steel is the predominant screen material, there are few reports of non-ferrous material screens. Therefore, in this study, we investigated the effect of a Ni screen on ASPN and S-DCPN. Low carbon steel S15C was treated by ASPN and S-DCPN using a Ni screen. A steel plate cold commercial (SPCC) screen was also prepared for comparison. Plasma nitriding was performed at 773 K for 240 min under an atmosphere of 75％ N₂ + 25％ H₂ at a gas pressure of 200 Pa. After the nitriding treatment, X-ray diffraction (XRD), glow discharge optical emission spectrometry (GD-OES), cross-sectional microstructure observation, surface microstructure observation, Vickers hardness test, and corrosion test were performed. As a result, when the Ni screen was used for S15C steel nitriding, more nitrogen atoms diffused into the sample than that when the SPCC screen was used; furthermore, nickel atoms diffused within the samples treated by both ASPN and S-DCPN using the Ni screen. ASPN-treated samples had less surface hardness and were higher corrosion resistance when prepared using the Ni screen than the SPCC screen. S-DCPN-treated samples had greater surface hardness and were less corrosion resistance when prepared using the Ni screen than the SPCC screen.

Fig. 7　GD-OES nitrogen profiles of S15C samples treated by (a) ASPN and (b) S-DCPN using Ni and SPCC screen.