Deposition mechanism of plasma sprayed droplets on textured surfaces with different diameter-to-distance ratios

The laser method was used to process dimples with different diameters and distances on ASTM 1045 steel substrates. Ni60 alloy powders were deposited on the textured substrates using atmosphere plasma spray technology. Single sprayed particles were collected to study the spreading behavior. Scanning electron microscopy was applied to characterize the cross-section morphology of splats and coatings, investigating the deposition behavior of droplets. Image analysis was used to calculate the open angle of first particle, thus also providing information on the subsequent particles. Transmission electron microscopy was used to investigate the crystal structure of coatings near the interface. The bonding strength of coatings was evaluated by pull-off tests. The impact of various texture parameters on the adhesion strength of coatings was investigated. The results showed that bonding strength improved with increasing texture diameter and decreasing texture distance. Wetting behavior between two particles as well as bond style between particles and substrates have great influence on bond strength of coatings with the variant texture diameter and distance. The diameter-to-distance ratio was found to be the factor directly determining the adhesion strength between substrates and coatings.