Characterisation of a commercial active screen plasma nitriding system

Hubbard, P 2007, Characterisation of a commercial active screen plasma nitriding system, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.

Document type: Thesis
Collection: Theses

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Title Characterisation of a commercial active screen plasma nitriding system
Author(s) Hubbard, P
Year 2007
Abstract Nitriding is a plasma based processing technique that is used to improve the surface properties of components and products in many areas including the aerospace, automotive and biomedical industries to name a few. Active Screen Plasma Nitriding (ASPN) is a relatively new nitriding technique which has potential advantages over the more traditional nitriding techniques such as Direct Current (DC) plasma nitriding where high substrate biases can be problematic. However, there is considerable debate as to the mechanism for nitriding in ASPN. This thesis focuses on investigating the mechanism for nitriding in a commercial ASPN system.

Commercial ASPN treatments of nitrideable alloy steels were found to be unsatisfactory unless a sufficient bias was applied. The level of bias required to produce a satisfactory nitriding response, in terms of the cross sectional hardness, was found to depend on the concentration of strong alloy nitride forming elements present in the steel.

Although active screen material was found to be transferred to the workload, no evidence was found that this process played a significant role in enhancing the nitriding response. The primary mechanism for nitrogen mass transfer in ASPN was found to be dependent on the active screen/workload separation distance. When this separation is small (less than approximately 10cm for the conditions used in this study) then nitrogen mass transfer in the form of energetic ions or neutrals can occur between the active screen and the workload. This allows samples to be treated without a substrate bias. On the other hand, when the active screen/workload separation distance is large (greater than approximately 10cm) as is normally the case in a commercial environment, this mechanism for nitrogen mass transfer breaks down and a substrate bias is essential. In this latter case, nitrogen ions attracted to the workload using a bias is the primary nitrogen mass transfer mechanism and the role of the active screen is primar ily to uniformly heat the workload.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Nitrides
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