Plasma Nitriding of AISI 304 Stainless Steel in Cathodic and Floating Electric Potential: Influence on Morphology, Chemi
- PDF / 8,927,732 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 105 Downloads / 165 Views
ASM International 1059-9495/$19.00
Plasma Nitriding of AISI 304 Stainless Steel in Cathodic and Floating Electric Potential: Influence on Morphology, Chemical Characteristics and Tribological Behavior Yang Li, Yongyong He, Wei Wang, Junyuan Mao, Lei Zhang, Yijie Zhu, and Qianwen Ye (Submitted June 30, 2017; in revised form October 10, 2017) In direct current plasma nitriding (DCPN), the treated components are subjected to a high cathodic potential, which brings several inherent shortcomings, e.g., damage by arcing and the edging effect. In active screen plasma nitriding (ASPN) processes, the cathodic potential is applied to a metal screen that surrounds the workload, and the component to be treated is placed in a floating potential. Such an electrical configuration allows plasma to be formed on the metal screen surface rather than on the component surface; thus, the shortcomings of the DCPN are eliminated. In this work, the nitrided experiments were performed using a plasma nitriding unit. Two groups of samples were placed on the table in the cathodic and the floating potential, corresponding to the DCPN and ASPN, respectively. The floating samples and table were surrounded by a steel screen. The DCPN and ASPN of the AISI 304 stainless steels are investigated as a function of the electric potential. The samples were characterized using scanning electron microscopy with energy-dispersive x-ray spectroscopy, x-ray diffraction, atomic force microscopy and transmission electron microscope. Dry sliding ball-on-disk wear tests were conducted on the untreated substrate, DCPN and ASPN samples. The results reveal that all nitrided samples successfully produced similar nitrogen-supersaturated S phase layers on their surfaces. This finding also shows the strong impact of the electric potential of the nitriding process on the morphology, chemical characteristics, hardness and tribological behavior of the DCPN and ASPN samples. Keywords
austenitic stainless steel, electric potential, plasma nitriding, wear
1. Introduction Plasma nitriding of austenitic stainless steels has been extensively investigated for research and applications in the last few decades (Ref 1-8). Ion and active species of nitrogen are generated by an electric discharge out of the thermodynamic equilibrium under low pressure and are then impinged (or absorbed) on the surface and diffused into the lattice sites of the austenitic. It has been demonstrated that the hardness and wear resistance can be improved by low-temperature (below 450 C) plasma nitriding without a loss of the corrosion resistance of the austenitic stainless steels. This process leads to the formation of a relatively high nitrogen content solid solution phase on the surface, which is known as the expanded austenite S phase, or cN phase (Ref 9-13). Yang Li, State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, Peoples Republic of China; and Department of Materials Science and Engineering, Yantai University, Yantai 264005, Peoples Republic of China; Yongyong He, Wei Wang, an
Data Loading...
