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With the conventional gas or water atomization process of synthesizing metallic powders, it is difficult to obtain graphite structure in a gray cast powder particle because of rapid cooling of the molten droplets. In this work, a fabrication method of gray cast iron powder with graphite structure was proposed based on a structural transplantation route. In the fabrication process, the precursor powder was firstly prepared by mechanically separating from as-cast gray cast iron bulk, then the precursor powder was ball-milled with different ratios of ball-to-powder to obtain final powders. The profile, size distribution, and surface roughness of final powders were quantitatively characterized by circularity, particle uniformity level, and fractal dimension method, respectively. It was found that ball milling smoothed the sharp edges and corners of the precursor powder and reduced the size of the precursor powder. As a result, the ball-milled powders have a more regular shape, more uniform size distribution, lower surface roughness, and better flowability than the precursor powder for thermal spray applications.

In this study, the bonding formation of the cast iron splat deposited on a preheated aluminum substrate by atmospheric plasma spraying was investigated using a finite element method based on a heat transfer model built in a cylindrical coordinate system. To enhance the accuracy of calculations, thermal contact resistance (Rth) of the contact interface was incorporated into the calculation. A precise Rth value was obtained using a well-established relationship. The diameter of grains in the splat was determined by atomic force microscopy analysis. Furthermore, the physical parameters of the cast iron and the aluminum at different temperatures used in the simulation were calculated according to the composition of the materials. The calculations indicated that the interface temperature was below the substrate melting point during the entire observation period, confirming that no melting of the aluminum substrate had occurred. Thus, the formation of splat–substrate metallurgical bonding was attributed to the enhanced interface temperature and plastic deformation rather than the melting of the substrate surface.

The properties of a thermally sprayed coating are primarily determined by the porosity and inter-lamellar bonding. In this work, three cast iron coatings were prepared by the atmospheric plasma spraying process. In the spraying process, the surface temperatures (deposition temperatures) of the coatings were controlled to be 50 ± 5, 180 ± 6, and 240 ± 8 °C. The microstructures of the coatings were characterized by field emission scanning electron microscopy. Both electrochemical polarization and immersion tests in 0.5 mol/L sulfuric acid solution were employed to evaluate the influence of deposition temperature on the corrosion behavior of the coatings. The results of these tests indicated that the coating deposited at high temperature shows a higher corrosion resistance than the coating deposited at low temperature, which was attributed to the reduced porosity of the coating resulting from the improvements in the flattening of the molten particles and the bonding between lamellae with raising the deposition temperature.

The size of the grains formed in individual splats has a significant effect on the properties of a thermally sprayed coating. In this work, the grain size in a plasma-sprayed cast iron splat was predicted based on a known relationship between the grain size and the thermal contact resistance at the splat–substrate interface. A numerical calculation method, based on a 2D heat transfer model, was used to study the relationship between the thermal contact resistance and the melting depth on the substrate surface. The thermal contact resistance was evaluated according to the observed maximum melting depth from the field emission scanning electron microscope micrographs of the individual splats. The estimated grain size with a range 51.3-73.6 nm was in close agreement with the experimental observations.

Amorphous coating technology is an attractive way of taking advantage of the superior properties of amorphous alloys for structural applications. However, the limited bonds between splats within the plasma-sprayed coatings result in a typically lamellar and porous coating structure. To overcome these limitations, the as-sprayed coating was treated by a laser-remelting process. The microstructure and phase composition of two coatings were analyzed using scanning electron microscopy with energy-dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction. The wear resistance of the plasma-sprayed coating and laser-remelted coating was studied comparatively using a pin-on-disc wear test under dry friction conditions. It was revealed that the laser-remelted coating exhibited better wear resistance because of its defect-free and amorphous-nanocrystalline composited structure.