OPTIMIZATION AND CONTROL OF A PLASMA CARBURIZING PROCESS BY MEANS OF OPTICAL-EMISSION SPECTROSCOPY

In this work optical emission spectroscopy (OES) is used to characteri ze the dissociation process of methane in an argon/hydrogen/methane di scharge for plasma carburizing. The optical emission spectra of the di scharge have been measured as a function of process parameters: discha rge voltage, pulse duration and pulse pause time. A correlation betwee n the intensities of hydrocarbon molecules, carbon atoms and ions, and the carbon mass flow model of the carburizing process has been confir med. The dominant species identified in the spectra used for correlati on 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 387.1 7 nm and 426.70 nm are also detected. It can be concluded that the int ensity of excited CH molecules at a molecular band at 431.42 nm is a f unction of pulse duration time, voltage and pulse pause time, respecti vely, indicating that carbon mass flow ((m)over-dot(c)) is directly pr oportional to the intensities of emission. This means that OES allows in situ, real-time control of the plasma carburizing process. (C) 1998 Elsevier Science S.A.