Numerical Investigation Method for the Determination of Electro- and Plasma-Chemical Portions in Current Signals from Plasma Electrolytic Oxidation Processes

The analysis of process signals is a key method for gaining experimental insight into the underlying layer formation mechanisms in plasma electrolytic oxidation (PEO). This is made possible by the simultaneous measurement of electrical and optical process signals with high temporal resolution. However, according to the current state of the art, the interaction between these signals is primarily discussed in qualitative terms. Therefore, this article presents a robust methodology for analysing the current signal, which makes it possible to categorise the charge electro-chemical and plasma-chemical dominated subprocesses and to quantify their respective contributions. The evaluation is performed by taking additional process signals into account. The experimental setup for measuring process voltage, current, and photovoltage, as well as the measurement routine, are briefly described. This is followed by a detailed description of the numerical procedure. This includes the application of fundamental mathematical methods to the time-discrete measurement data, the automated selection of the pulse segment to be examined and the identification of discharge initiation to determine the interval boundaries of the electro- and plasma-chemically dominated pulse subsegments. The description of the routine is primarily intended for experimental scientists and is meant to provide them with a tool for extracting additional information from their process data. These can then be used to better understand electro-chemical side reactions and parasitic subprocesses in PEO.