Abstract No.:
2815

 Scheduled at:
Wednesday, September 28, 2011, Saal A 2:00 PM
New Processes 2


 Title:
Effect of nitrogen flow rate on mechanical properties of metallic coatings by warm spray deposition

 Authors:
Makoto Watanabe* / National Institute for Materials Science, Japan
Christoph Brauns / National Institute for Materials Science, Japan
Masayuki Komatsu/ National Institute for Materials Science, Japan
Seiji Kuroda/ National Institute for Materials Science, Japan
Hiroshi Katanoda/ Kagoshima University, Japan
Frank Gärtner/ Helmut Schmidt University, Germany
Thomas Klassen/ Helmut Schmidt University, Germany

 Abstract:
In Warm Spraying (WS), the temperature of the combustion flame is reduced and controlled by injecting nitrogen gas before the converging section of the Laval nozzle and before the injection of spray powders. Thus, temperatures of spray particles are kept under their melting points with moderately heated and thermally softened states.

As compared to HVOF-spraying, the oxidation of particles can be significantly suppressed due to lower deposition temperatures, whereas, as compared to cold spraying, the degree of particle deformation upon impact can be enhanced by attaining higher particle temperatures. Larger deformation is usually preferable to assure better bonding onto the substrate and within the coating. Since WS bridges the gap in particle temperatures between HVOF and cold spraying, it is important to understand the effects of particle temperatures on the microstructures and mechanical properties of WS coatings.

In the present study, Ti, Cu, and Al coatings were fabricated by WS under various nitrogen flow rates. Higher nitrogen flow rates reduce the particle temperatures. The mechanical properties of the coatings were evaluated by tubular coating tensile (TCT) and micro flat tensile (MFT) tests. The respective strengths can be explained by differences in coating microstructures. For the lower impact temperature regime, the coatings became denser and the ultimate strengths of Ti or Cu coatings increased reaching a maximum by decreasing the nitrogen flow rates. A further decrease of nitrogen flow rates and reaching the upper temperature regime reduced the coating strength, probably due to oxide formation at particle-particle boundaries and thus less inter-particle cohesion. These results clearly demonstrate how particle temperatures affect the microstructures and mechanical properties of WS coatings and that optimum spray conditions have to be balanced between softening and oxidation by adjusting particle temperatures for the best performance of the respective spray material.


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