SURFACE TREATMENT OF STEEL WITH ION BEAM IMPLANTATION USING PLASMA FOCUS

Abstract

Plasma nitriding by using a Mather-type plasma focus device is a technique that is not very well explored but it can be used to increase the surface hardness of low carbon steel and to enhance its wear resistance for application as a cutting and machining tool. A column of hot and dense plasma made out of nitrogen ions bombarded on the target surface creates a nitride layer by embedding nitrogen ions on the target surface. It results in modified surface hardness and structure.

In this thesis, a study on the nitriding effects of a 3 kJ Mather-type dense plasma focus (DPF) device in a low-pressure nitrogen atmosphere is carried out using the INTI International University plasma focus machine. Experiments were repeated multiple
times by keeping nitrogen gas pressure constant at 0.5, 1, 1.5 and 2 Torr and placing properly cut and polished low carbon steel samples at fixed distances of 40, 60, 80,100 and 120 mm from anode. It was found that if the INTI International University plasma focus machine is to be used for material hardening, the best results will be obtained at 1 Torr with the target placed at a distance of 40 mm from the anode. It correlates with the prediction made by Lee Model Code which predicts the production of highest energy beam at Nitrogen pressure of 1 Torr in numerical experiments of an earlier study by A. Singh [62]. The central region where the ion beam was concentrated was the region where the hardness was most noticeably improved.

The dense plasma focus device delivered a surface texture of overlapping dimples on the surface of the target. This surface texture can be employed as a base for the application of lubricant in the making of a textured cutting tool for the purpose of dry machining. One of the hardened (nitrided) sample was tested on an aluminium work piece. Cutting was easy and there was no visual indication of aluminium sticking to the rake face of the tool which are prominent indicators of improved hardness and effectiveness of surface patterns produced by DPF during the nitriding process.

Results from our experiments conclude that the DPF machine can be utilized for localized surface nitriding with an additional advantage of surface patterning. The best hardening can be achieved at nitrogen gas pressure of 1 Torr when the sample is placed at 40mm from the anode. Such a hardened steel has great potential as an efficient cutting and machining tool.