Basic investigations on low-pressure plasma nitriding at high voltages

• Applicant: Professor Dr. Günter Bräuer
• Subject Area: Coating and Surface Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544130010

Plasma nitriding is an established thermochemical process to increase the corrosion and wear resistance of steels. It has been used successfully in the industry for decades to optimize components and tools for their intended use. Technological developments in the field of voltage supply and suitability for plasma nitriding have not yet been scientifically investigated. Novel plasma generators with improved arc management enable plasma nitriding processes at significantly higher voltages than is common in industry today. This extended process control is to be investigated in the applied project. Preliminary tests carried out in this area are promising and show that high voltage has a significant influence on the formation of the nitrided zone. In several tests with high voltage, among other things, a significantly accelerated growth of the compound layer was demonstrated. This could allow more economical processes, e.g. in the area of oxynitriding. In this process, a compound layer is first generated in a two-stage process and then oxidized to magnetite in a second process step. The process can be significantly shortened in time by using high voltage to generate the compound layer. The aim of this project is to scientifically investigate and understand in which way high process voltages influence the plasma and the nitriding result. To this end, the relationship between plasma characterization and the arising nitriding result will be investigated. For this purpose, extensive nitriding processes will be carried out with different materials (a high-alloyed as well as a low-alloyed ferritic steel, an austenitic steel and a titanium material). The process parameters pressure, pulse-pause ratio, gas composition and temperature are varied individually under the influence of high voltage. During the process, the plasma is characterized using optical emission spectroscopy. In this way, the changes in the plasma are correlated with the nitriding results in order to determine how the plasma influences the diffusion process. Preliminary work has already shown that the current increases disproportionately with increasing voltage. It is assumed that an increased ionization rate of the plasma is responsible for this. The project will explain the fundamental influence of high voltages in plasma processes on the near-edge modification of metallic surfaces and thus enable ecologically optimized process control in the future.

• DFG Programme: Research Grants