This paper describes the development of cold-sprayed chromium coatings that are used to increase the corrosion and wear resistance of zirconium-based nuclear fuel cladding tubes. Significant effort was necessary to deposit very thin layers of chromium on 4 m long, 10 mm diameter tubes by cold spraying. As explained in the paper, a final polishing step is used to reduce surface roughness and adjust coating thickness to the desired specifications.

Titanium has an excellent corrosion property in chloride containing environments such as seawater. A modified HVOF spray process was developed by introducing a mixing chamber between the combustion chamber and the powder feed port. Nitrogen gas was fed into the mixing chamber to control the temperature of the combustion gas generated in the combustion chamber. By controlling the flow rate of nitrogen, various Ti coatings with different degree of oxidation and porosity could be fabricated. The densest coating produced by this process with surface polishing treatment maintained excellent corrosion protection over a steel substrate in artificial seawater in a laboratory test over 1 month.

A systematic study of sample preparation methods tailored to different types of thermal spray coatings was recently conducted. This paper presents the results of investigations on polishing methods and materials and their effect on the quality of cuts. The results show that the type of polishing cloth used has a major influence on layer breakouts, while the direction of rotation and embedding medium have relatively little effect. Paper includes a German-language abstract.

The metallographic process for evaluating thermally sprayed coatings is sometimes viewed as a variable process in the scope of coating evaluation. There is always a question as to whether the failure of a coating is polishing related or an actual change in the spray production process. The use of metallographic standards similar to hardness calibration can be implemented to provide assurance of a repeatable metallographic polishing. Development and use of the standards will be discussed and examples given of the standards principle.