Microstructure of plasma-sprayed cast iron splats with different particle sizes

The superior wear-resistant property of cast irons is closely linked with their microstructure, in which graphite formation in plasma-sprayed cast iron coatings causes distinct characteristics owing to its self-lubricating property. Since the solidification rate generally affects graphite formation, the optimum in spray parameters such as substrate temperature, ambient pressure, particle size and spray distance is required to slow down the solidification rate, as well as to improve the adhesive strength of splats. In this study, cast iron splats were induced on an aluminum alloy substrate by plasma spraying using alloyed cast iron powder high in silicon and aluminum in a low pressure argon atmosphere. Then, the effects of particle size on the microstructure and adhesive strength of splats were investigated by introducing the correlation between the solidification rate and the microstructure. Spraying with large particles leads to an increase in the number fraction of disk splats and a slight decrease in their adhesive strength. Cross-sectional observations reveal fine graphite growing in splats nearly perpendicular to the substrate surface