Microstructure and age characterization of Cu-15Ni-8Sn alloy coatings by laser cladding

The present work has investigated the influence of direct aging treatment on the precipitation sequence and properties of the Cu-15Ni-8Sn alloy coatings prepared by laser cladding. The experimental results show that the tendency of Sn segregation in the conventional Cu-15Ni-8Sn solidification microstructure is effectively relieved. Before aging, there are only two phases in the coating: the α-Cu solid solution dendrites with 7 wt.% Sn solubility, and a small fraction of Sn-enriched δ-phase at the interdendrites in rapid solidified microstructure. After the coating was directly aged at 370 °C without traditional solution pretreatment, the α-Cu solid solution dendrites experience precipitations in the order of pure spinodal decomposition, DO22-ordered structure and discontinue γ-DO3. The microhardness of the coating treated by direct aging reached 390 HV 0.5, which was higher than that treated by conventional solution and aging process owing to the solidified fine grains and hardening effect of spinodal decomposition. In addition, the Sn-enriched δ-phase at the interdendrites also decomposes to laminar discontinuous precipitated γ-DO3 phase after aging. Precipitation sequence and properties of the clad coatings change obviously during the direct aging treatment.