Advantages of Mn-Bronze for Cold Spray Applications

Monday, May 27, 2019: 11:00
Annex Hall/F206 (Pacifico Yokohama)
Dr. Frank Gaertner , Helmut Schmidt University, University of the Federal Armed Forces Hamburg, Hamburg, Germany
Dr. Sebastian Krebs , Helmut-Schmidt University, University of the federal Armed Forces Hamburg, Hamburg, Germany
Prof. Thomas Klassen , Helmut Schmidt University, University of the Federal Armed Forces Hamburg, Hamburg, Germany
High strength bronze coatings are of high interest for cavitation protection of ship rudders or for ship propeller repair. By avoiding oxidation, cold spraying appears as suitable method to achieve the needed strength and cavitation resistance needed in such marine applications. Recent studies showed that attainable coating qualities by cold spraying of Ni-Al propeller bronze are limited by metastable, martensitic phases being present in the gas atomized powder.

Despite showing a similarly high strength of about 1300 MPa, cold spraying of Mn-bronze powders at similar parameter sets results in better coating qualities than obtained for Ni-Al-bronze. As proven by negligible porosity, high cavitation resistance, as well as high coating hardness and electrical conductivity, bulk like properties were obtained at impact velocity to critical velocity ratios of 1.3, instead 1.5 or higher as for usual cold spray materials. According to X-ray diffraction, the unexpected high coating quality can be attributed to a solid-state transformation from bcc powder to the denser and softer fcc coating structure by the pressure pulse upon impact. Thus, coating qualities, particularly a high cavitation resistance in marine applications, can be obtained that are not reachable by cold spraying of other bronze alloys.

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