| DC-Plasma Jet Surface metallurgy is the advancing sub ject study of surfacematerial. As a cross subject of DC-Plasma Jet Surface metallurgy and fast freezingtheory, it has important study meaning. DC-Plasma Jet Surface metallurgicaltechnology was applied successfully in shock-resistant, wear-resistant andcorrosion-resisting filed, such as mine, metallurgy, architecture and militaryindustry, because of unique performance. It is necessary to study the mechanismof DC-Plasma Jet Surface metallurgical technology because the technology ontheoretical research is far more behind its using in practical engineering.In the paper, the technical principle, the equipment and design of Fe-basedalloy of DC-plasma jet surface metallurgy have been discussed. The electric-arcaction of plasma-jet and acquirement and transform of plasma beam in the processof DC-plasma jet surface metallurgy have been also studied in the paper.On base of the principle of alloy design and a large number of tests, Fe-basedcoating has been produced by DC-plasma jet surface metallurgy. The regionalmetallurgical process, flowing characteristics of melt, the chemical metallur-gical process and temperature field of the molten bath have been analyzed in full.Making use of optical microscope, SEM, electron probe, X-ray diffraction etc.,morphology and component features have been studied in detail. The metastablestructure in the alloy coatings was made up of complex phases containingsupersaturatedγdendritic crystal, which was solid solution of many alloyelements, and eutectic structure ofγ+alloy carbide. The eutectic structureswere uniform and tiny had they had multi- morphology as sheet, fishbone, dendritesand graininess. The different solidifying structural morphologies, varying fromplanar crystal in interface of coating/substrate to celtuler/dendritic crystal,then to equiaxed crystal in middle of the coating, were controlled by courseof rapid heating, rapid solidification and intensive convection which appearedin different region along the molten pool. There was an especial non-crystallinestructure in Fe-Cr-V-Ti-Ni-Nb-Si-B-C coating, which is Ti-base non-crystalline phase. It may correlate with component change in part micro-area.In this paper, the defects of gas cavity and crack have been involved formview of the metallurgical factor and electromagnetism influence. Adding properlyalloy elements can reduce molten bath viscosity, which advanced the melt flowby dint of surface tension, buoyancy action, plasma airflow and self-inducedelectromagnetic force. The sufficient flow can increase the rising speed of airbubble; thereby it can reduce the probability of air bubble. The crack inmetallurgical coating correlated with processing parameter, the percentagecomposition of alloy powders in metallurgical material and subsequent heattreating.
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