Surface structures are of vital importance for the wetting behaviors of hydrophobic coatings. In this work, rare earth oxide coatings with different surface structures were deposited via the solution precursor atmospheric plasma spray (SPAPS) process and solution precursor vacuum plasma spray (SPVPS) process, respectively. The SPAPS coatings showed hierarchical cauliflower-like surface structures composed of micron-sized clusters and nanometer-sized particles, while the SPVPS coatings showed relatively flat topographies with small and short bumps. The formation of different surface structures in the SPAPS and SPVPS processes was investigated by modelling the movement of in-flight particles in the vicinity of the substrate. The properties of plasma jets and the characteristics of in-flight particles in the two processes were correlated. The effects of diverted plasma gas flow on the trajectories of particles impinging on the substrate and the resultant surface structures were elaborated, revealing different shadowing effects in the SPAPS and SPVPS processes. The SPAPS coatings were superhydrophobic due to the presence of hierarchical surface structures, which showed larger water contact angles and smaller roll-off angles than the SPVPS coatings. The correlations between the surface structures and wetting behaviors of different coatings were investigated.

Aerosol deposition (AD) is a novel method for producing dense nanocrystalline ceramic films at room temperature. Previous studies primarily used flat substrates with varying hardness and roughness. However, the development of micro-device applications is increasing the demand for deposition on structured/patterned surfaces. To investigate the impact of substrate patterns on coating microstructure and growth mechanisms in AD, alumina coatings were deposited on patterned Si substrates. Si wafers with patterns of micropillars were employed. The coatings were characterized using laser scanning microscopy, scanning electron microscopy, and x-ray diffraction. The microstructure and density of coatings in the valleys were influenced by the size of and the spacing between the patterns. The results revealed that coatings initially formed in the valleys before covering the entire pattern. Fragments of the initial powder particles became trapped between the patterns, adhering to the groove bottoms and pillar sides. Subsequent particle impacts and densification processes transformed these fragments, ultimately filling the gaps between the walls. With further deposition, a uniform coating surface was achieved.

The plasma jet in the vacuum plasma spray process presents characteristics such as supersonic flow, expanded jet dimensions, and a smaller decay rate for jet velocity and temperature that are distinctly different than in atmospheric plasma spray. In this work, a solution precursor vacuum plasma spray (SPVPS) process is described, which combines vacuum plasma spray with solution precursor as the feedstock. The deposition of superhydrophobic ceramic coatings via the SPVPS process is explored. Yb 2 O 3 coatings are deposited by a radial injection of Yb(NO 3 ) 3 solution in the anode of an F4-VB torch operating under a pressure of 150-250 mbar. Solution precursor atmospheric plasma spray (SPAPS) is also applied to deposit superhydrophobic Yb 2 O 3 coatings for comparison with the SPVPS process. The wetting behaviors of the coatings are characterized by water contact angle measurement, water rolloff test, and dynamic water impact test. The experimental setup, plasma jet characteristics, interactions of solution droplets and plasma, microstructure and wetting behaviors of coatings in the two distinct processes are compared and discussed.

The application of metallic foam core sandwich structures in engineering components has been of particular interest in recent years because of their unique mechanical and thermal properties. Thermal spraying of the skin on the foam structure has recently been employed as a novel cost-efficient method for fabrication of these structures from refractory materials with complex shapes that could not otherwise be easily fabricated. The mechanical behavior of these structures under flexural loading is important in most applications. Previous studies have suggested that heat treatment of the thermally sprayed sandwich structures could improve the ductility of the skins and so affect the failure mode. In the present study the mechanical behavior of sandwich beams prepared from arc sprayed alloy 625 skin on 40 ppi nickel foam was characterized under four point bending. The ductility of the arc sprayed alloy 625 coatings was improved after heat treatment at 1100°C and 900°C while the yield point was reduced. Heat treatment of the sandwich beams reduced the danger of catastrophic failure.

Yttrium oxide (Y 2 O 3 ) can be used in different applications such as corrosion resistance, high temperature applications and semi-conductor production equipment due to its very high thermal and chemical stability. In the current research, yttria coatings were processed using a new type of DC plasma gun consisted of molecular gases CO 2 +CH 4 . Physical and structural properties were compared with the coating made by SG-100 plasma torch. Gas mixture of CO 2 +CH 4 improves the torch efficiency due to its high thermal enthalpy and conductivity which leads to increased particle temperature and complete fusion of the sprayed particles during the process of coating. SEM study of the structure revealed that the coating has higher density and lower porosity compared to the coating produced by SG-100 torch. No unmelted particles can be observed in the coating. XRD analysis of the coating showed that the coating contains no amount of harmful metastable monoclinic phases. This all proves the better quality of the coatings deposited by CO 2 +CH 4 gas mixture in comparison to the conventional coatings.