| Abstract | The feasibility of depositing W-Cu composite overlays on bronze substrate by laser cladding technique was explored. Two types of tungsten powders, with an average size of 10μ and 32μ, were used to deposit coatings with various thicknesses. Metallographic analysis of the composite coatings reveals that, due to the poor wetting behavior, tungsten particles tend to separate from the copper molten pool or coalesce and segregate within the molten pool. The coalescence and separation of the particles occur more easily for the fine powders then for the coarse ones, making it simpler to deposit dense and uniform coatings using coarse tungsten powders. Laser cladding of dense and uniform coatings thicker than 1mm was proven to be difficult, because the separation of tungsten particles from copper substrate occurs after reaching a certain coating thickness, forming a tungsten particles-free copper layer covered with a tungsten particles-rich layer. After these partition layers develop to their critical thickness, localized separation occurs, resulting in a series of tungsten-free copper area surrounded by tungsten particles-rich areas. Nickel addition enhances the possibility of depositing uniform and dense W-Cu composite coatings, preventing or limiting the segregation and separation of constituents. The preliminary results indicate that, by adjusting processing parameters and powder-blend compositions, it is feasible to fabricate dense and uniform W-Cu overlays with various thicknesses that are metallurgically bonded to the substrates. |
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