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.

Thermally sprayed coatings with Co-based alloy were evaluated for cavitation erosion resistance in order to use as erosion proof coatings. Co-based alloy coatings have been applied by Low Pressure Plasma Spray (LPS) and High Velocity Oxygen Fuel Flame Spray (HVOF) on the AISI 403 stainless steel substrates and half number of each coated specimen were post-heated at 1073K for 1 hour. The mass loss was measured for evaluation in this study. The following results have been obtained in the cavitation test; i) Both of LPS coatings (the post-heated and the as sprayed) have more excellent cavitation erosion resistance than HVOF coatings, ii) With regard to LPS coatings, the post-heated coating has the same weight loss as the as-sprayed coatings. iii)The post heat treatment to HVOF is remarkably effective to improve the cavitation erosion resistance.

The work reported herein deals with the interaction among the thermally sprayed coatings and steel substrate in acid aqueous solutions investigated by using the electrochemical process. Thermally sprayed coatings on steel substrate for such as the tribological applications except for the sacrificial anode property have been extended. The environment of these machinery components is often utilized accompanied with the aqueous solutions. The galvanic corrosion occurred in aqueous solutions among the metals or alloys have been well known. In the actual spray process, the formation of penetrated pores or crevice defects are not generally avoided. In the aqueous solution environment, the penetrated defects cause the galvanic corrosion between coating and steel substrate, and tend to be occurred the coating spalling. In this work, the electrochemical process was employed to determine the corrosion phenomena. The preferable combination of sprayed coatings and steel substrate are discussed and the examples of design of the intermediate layers are proposed.