Thermal sprayed ceramic coatings are well used as the electrode of corona discharge treatment in order to modify the surface of many kinds of films and papers due to its superior durability and adaptability. Some kinds of Al 2 O 3 -TiO 2 were sprayed by APS on the parallel plate electrodes, and output power of corona discharge generated by the electrodes was measured by using Sawyer-Tower circuit. In addition, discharge output power was calculated with an equivalent circuit of corona discharge. By comparing them, effects of the electrical property of the coating on discharge was researched. As a result, the electrostatic capacitance of the coatings influences the impedance of the whole circuit, and higher relative permittivity of the coating brought higher output power in a constant voltage.

Damage of marine screw propeller parts made of aluminum bronze cast material caused by cavitation erosion is one of the serious problems. Erosion resistant thermal spray coating on aluminum-bronze material is expected to extend lifetime of such propellers. In this study, Cobalt-based alloy coatings sprayed by; (a) atmospheric plasma spraying (APS), (b) low pressure plasma spraying (LPPS) and (c) high velocity oxy-fuel (HVOF) spraying and aluminum bronze cast material were evaluated by cavitation erosion test using magnetostrictive cavitation test equipment. Fracture morphology of cavitation eroded coating surfaces were analyzed by surface observations with SEM and also the amount of volume loss was measured. Cobalt-based alloy coatings sprayed by LPPS exhibited superior cavitation erosion resistance compared to aluminum bronze cast material and coatings by APS and HVOF. Moreover, mechanical properties of Cobalt-based alloy coatings were investigated in detail by nanoindentation technique. It is found that cavitation erosion resistance of coatings is subjected to interparticle cohesive strength.

A copper electroplating method revealed that recently developed commercial Al 2 O 3 thermal spray coatings did not have the well-known lamellar structure but instead had a structure that was made up of tightly bonded particles, with many vertical microcracks in the coating. The coating in the study was prepared by the atmospheric plasma spray system. The copper electroplating method was applied to observation of the Al 2 O 3 thermal spray coating structure. Spray coating specimens were electroplated in an aqueous solution containing CuSO 4 , H 2 SO 4 , CuCl 2 , and additives so that copper was deposited in small pores and narrow cracks in the coatings. Copper in the Al 2 O 3 coatings was observed clearly by scanning electron microscopy, which also revealed the coating’s structure (boundaries of flattened particles and vertical cracks). The coating did not have a lamellar structure (horizontal apertures between flattened particles) and it was dense in spite of the many microcracks.

Mechanical properties of thermal-sprayed ceramic coatings were investigated. Al 2 O 3 and Y 2 O 3 -stabilized ZrO 2 (YSZ) coatings were deposited on plate substrates. Stainless steel plates and aluminum plates, of different thermal expansion coefficients, were used as substrates. The coatings were prepared at two different thicknesses. During deposition of each sample, the history of substrate temperature was recorded. Four-point bending tests were carried out, while strains at the coating surface and the substrate surface were measured with strain gages. The apparent Young's modulus of the coating was determined using the composite beam theory. In addition, the rupture strain of the coating was measured by three-point bending test. The relationship between the results of these tests and the temperature of each substrate during deposition is discussed.

In plasma spraying, generally, powders are radially injected into plasma jet. However, percentage of particles which have enough enthalpy to melt is not high in radial injection, possibly leading to low deposit efficiency especially for high melting point powders. In this research, powder port for radial injection was attached to an axial injection plasma torch in order to compare the plasma flame in both cases of axial and radial powder injections. The powder trajectory and the shape of the plasma plume were observed, and particle flux density, temperature, velocity, and deposit efficiency of alumina powders were measured and the results were compared between the two powder injection methods.