During atmospheric plasma spraying, considerable changes of alloy powder particles often occur. Besides spheroidization, this refers particularly to alloy composition. The present paper describes the results of a study of decarburization and oxidation of cast iron powder at the in-flight period of spraying by a water-stabilized plasma torch. Both reactions were affected significantly by particle size and feed rate. The reactions are a consequence of oxygen entrainment from the ambient atmosphere. In some cases, extreme decarburization was observed. Average surface temperature and average particle velocity were measured in selected spraying runs along the main part of the particle path in the plasma stream. Information on structure of sprayed cast iron powder as compared with feedstock powder was obtained by Mossbauer spectroscopy. To maintain the cast iron properties, as large particle size and high feed rate as possible are necessary. Based on experimental results, the decarburization mechanism is considered.
展开▼
