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5481 |
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Wednesday, June 07, 2017, Hall Y 2:20 PM Maritim Industry & Off-Shore Technologies |
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Influence of the substrate thickness on properties of cold gas sprayed bronze coatings |
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Maria Villa-Vidaller* / Helmut-Schmidt-University of the Federal Armed Forces, Germany Gärtner Frank / Helmut Schmidt University, Germany Capitano Stefano/ Università degli studi di Modena e Reggio Emilia, Italy Klassen Thomas/ Helmut Schmidt University, Germany |
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Despite the progress in fluid mechanics during the last decades, ship propellers still suffer from cavitation erosion, demanding for substitution or repair. Due to thermal shrinkage and associated stresses, the restoration of the original shape by weld cladding is restricted. A possible alternative, imposing less heat and stress into the part, is given by cold spraying. However, the locally differing thickness of affected fin edges might influence attainable coating properties. The aim of the present work is to quantify possible influences by studying effects of defined substrate thickness on the properties of cold gas sprayed bronze coatings. To mimic the repair of ship propellers, nickel-aluminium bonze was chosen to serve as spray powder and substrate material. Cold spraying was applied on substrates with different thicknesses, varying from 5 to 30 mm. For enhancing the influence of substrate thickness on expected properties, the coatings were sprayed with about just critical conditions for bonding, means an impact to critical velocity ratio · (eta) of about unity. First layer adhesion and bonding mechanism were evaluated by analysing single impacts (wipe-tests). Apart from microstructural analyses, the coating performance was investigated by modified cavitation and coating conductivity tests. The results demonstrate that deposition efficiency, electrical conductivity and cavitation resistance increase with decreasing substrate thickness as well as a reduction in porosity. Trends of change are less pronounced for large substrate thickness. The variance in coating properties with substrate thickness can be explained by higher effective surface temperature on thinner substrates due to lower effusivity. Extrapolating respective correlations to higher parameter sets, allows for estimating condition to improve coating qualities by means of substrate heat to meet the challenges for ship propeller repair. |