DC plasma is a very promising technology for processing different materials, and is becoming especially interesting when low environmental impact and high-performance treatments are needed. Some of the intrinsic characteristics of DC plasma technology, which make it suitable for powder metallurgy (PM) and powder injection molding (PIM) parts production, are lowpressure processing and plasma environment high reactivity. Moreover it can be considered as a highly competitive green technology. In this work, an overview of some of the important DC plasma techniques applied to PM and PIM parts processing is presented. Emphasis is given to the descriptions of the main characteristics and the technique potentials of plasma-assisted nitriding, plasma-assisted thermal debinding, plasma-assisted sintering, and simultaneously plasma-assisted sintering and surface alloying. The aspects presented and discussed in this paper indicate that DC plasma processes are promising and competitive techniques for PM and PIM parts processing.
The influence of the content and nature of impurities on the rotational temperature of three probe molecules (OH, NH and
) in a helium plasma created in a microwave resonant cavity is investigated by the synthetic spectra method and by mass spectrometry. OH is found to be the only reliable probe to obtain a satisfactory estimation of the gas temperature. In our experimental conditions, depending on the impurity, the gas temperature varies strongly and at 500 ppm, for instance, a difference of 700 K is possible (∼30% of the mean temperature).
A collisional–radiative model is proposed to describe the behaviour of a helium plasma sustained in a resonant cavity at atmospheric pressure. A set of rate constants is proposed at 2450 K. Indeed, most of the available data in the literature are reliable below 500 K. It is shown that the time post-discharge is mainly controlled by ambipolar diffusion during the first ten µs, next by electron-assisted recombination of helium ions and finally by chemionization from the excited state. This post-discharge lasts for hundreds of µs. It is mainly due to the slow recombination of electrons together with chemionization. Then, at steady state in CW mode, the electron temperature is found to be lower than 1 eV since low reduced fields are needed to sustain the discharge.
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