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4872 |
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Tuesday, May 10, 2016, Auditorium 11:30 AM Cold Gas Spraying I |
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Substrate effect in cold spraying |
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Hamid Assadi* / Helmut Schmidt University
Dept. of Mechanical Engineering, Germany Maria Villa-Vidaller / Helmut Schmidt University, Germany Zohreh Arabgol/ Tarbiat Modares University, Iran Frank Gärtner/ Helmut Schmidt University, Germany Thomas Klassen/ Helmut Schmidt University, Germany |
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The intrinsic properties of cold-sprayed deposits are typically considered to be a sole function of the spraying parameters that determine particle impact conditions, hence to be independent of substrate properties. The present paper demonstrates that, contrary to this common notion, the coating quality can indeed be much influenced by substrate properties, even in regions far (up to a millimetre) away from the substrate/coating interface. This is pursued through multi-scale modelling of cold spraying, combined with systematic experimentation. Cold spraying was performed with titanium and copper powders at fixed spraying parameters, but with different substrates held at different predefined initial temperatures. The results of electrical conductivity measurements, carried out on the top layer of the coatings, showed a significant effect of substrate type and temperature on the coating quality. The results of modelling showed that this effect relates to the thermal rather than mechanical properties of the substrate. The former, together with the initial substrate temperature, affects the instantaneous temperature of the top layer of the surface of the already deposited material upon particle impact, which in turn influences the flow stress of the material, hence the extent of bonded area and coating quality. Moreover, the mechanical properties of the substrate are shown to influence the coating properties up to a maximum of 50 microns. These findings also underline the role of thermal management, e.g. through spraying kinematics, in cold spraying. |