Investigation on morphology and micro-hardness characteristic of composite coatings reinforced by PTA copper alloying on nodular cast iron

Abstract

In this study, plasma transferred arc (PTA) surface alloying was used to study the relevant technology of preparing a reinforced layer made of copper-bearing particles onto a nodular cast iron (NCI) surface. To conduct a multi-aspect study of the technological characteristics of copper alloying, three process parameters, including the height between the plasma torch nozzle and the substrate surface (nozzle height), the normal direction angle between the plasma arc and the substrate surface (deflection angle), and the spacing of the plasma arc's scanning track (scanning space), were considered. The effects of these process parameters on the alloyed molten pool morphology and micro-hardness were mainly investigated. The results demonstrated that the nozzle height not only had a significant effect on the integration of copper particles into the NCI surface, but also could affect the alloyed morphology and micro-hardness evolution. In particular, when the nozzle height was 4 mm, the depth and micro-hardness of the alloyed molten pool reached their maximum values. Additionally, the deflection angle and scanning space were also shown to affect the shape of the alloyed molten pool. There was a linear relationship between the value of the alloyed molten pool and the deflection angle, and a large difference between the hardness and the microstructure was found between different scanning spaces.