Optimization and control of a plasma carburizing process by means of optical emission spectroscopy

Abstract

In this work optical emission spectroscopy (OES) is used to characterize the dissociation process of methane in an argon/hydrogen/methane discharge for plasma carburizing. The optical emission spectra of the discharge have been measured as a function of process parameters: discharge voltage, pulse duration and pulse pause time. A correlation between the intensities of hydrocarbon molecules, carbon atoms and ions, and the carbon mass flow model of the carburizing process has been confirmed. The dominant species identified in the spectra used for correlation are excited and ionized carbon atoms, as well as excited carbon and hydrocarbon molecules such as excited CH with a molecular band at 431.42 nm and 314.41 nm, and excited C 2 with a molecular band at 501.50 nm. Excited carbon atoms at 493.21 nm and excited carbon ions at 387.17 nm and 426.70 nm are also detected. It can be concluded that the intensity of excited CH molecules at a molecular band at 431.42 nm is a function of pulse duration time, voltage and pulse pause time, respectively, indicating that carbon mass flow ( ṁ c ) is directly proportional to the intensities of emission. This means that OES allows in situ, real-time control of the plasma carburizing process.