Abstract
This paper is devoted to the investigation of the formation of dual diffusion layers during low-temperature ( T < 420 °C) plasma-assisted nitriding (PAN) of austenitic stainless steels. New experiments are presented and compared with previous published results. It is shown that a cleaning pre-treatment in Ar–H 2 before PAN produces a double-layer structure. Two distinct layers with well-defined interface are observed by SEM. SNMS depth profile measurements show that the inner layer is due to a carbon solid solution phase ( γ C) located at the interface with the bulk substrate and the outer γ N layer. It is shown that carbon contamination is responsible for the formation of this γ C sublayer. Carbon contamination is observed only when an in situ cleaning procedure in Ar–H 2 is performed before a nitriding treatment. A discussion on the origin of this carbon contamination is presented and it is also explained why it occurs in Ar–H 2 discharges and not in N 2–H 2 discharges.
Published Version
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