Abstract
Cylindrical samples of AISI 1020 steel were nitrided, using the techniques of conventional plasma nitriding and cathodic cage. In the latter, the samples are kept at floating potential, inside of a cage that works as a cathode and to shield the samples from the cathodic potential. A systematic study was conducted in order to evaluate the efficiency of this technique in the elimination of edge effect, in comparison with conventional plasma nitriding. In addition, another comparative study of the phases obtained using the conventional plasma nitriding and nitriding with cathodic cage was performed. Two metallic cages were used, one made of austenitic stainless AISI 316 and other one made of AISI 1020 steel, to prove the effect of deposition in nitriding with cathodic cage. The samples which were nitrided by this new technique had shown nitriding rates, crystalline phases, and microhardness, similar to those samples which were nitrided conventionally. However, it was possible to confirm the elimination of edge effect through the characterization by optical microscopy and by microhardness test along the samples surfaces. The samples were characterized by optical microscopy, microhardness tests and X-ray diffraction.
Highlights
The conventional plasma nitriding (DCPN) is interesting for industries due to the important benefits in superficial properties
The nitrided samples show that the conventional plasma nitriding (DCPN) produces a non-uniform surface layer, and its color varies from the center to the periphery of samples nitride[6,8]
This phenomenon can be seen without microscope and it is known as edge effect that is a common problem associated with the DCPN process, triggered by competition between sputtering and deposition during the process, due to changes in the electric field in the corners and edges, as showed in the Figure 2a
Summary
The conventional plasma nitriding (DCPN) is interesting for industries due to the important benefits in superficial properties. The process has been successfully applied to steels of low alloy, tool steels and stainless steel[1]. It is used for improvements of surface properties such as hardness, resistance to wear and corrosion, with the goal of increasing the life of parts nitrided. It shows some drawbacks as edge effect, hollow cathode effect, non uniform temperature and opening of arches, especially in the treatment of parts with complex geometry[2,3,4].
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