The role of deposition sequence in cold spraying of dissimilar materials

Cold spraying of dissimilar materials have been addressed to understand the role of deposition sequence on the characteristics of the coating/substrate interface. Nickel and titanium coatings were sprayed onto the substrates of the opposite material under different conditions. The samples were subsequently heat treated, to better reveal the quality of metallic bonding at different locations, and examined by mechanical testing and microstructural analysis. The results show that the bonding characteristics of the Ni(coating)/Ti(substrate) pairs are significantly different from those of the Ti(coating)/Ni(substrate) pairs. Mechanical interlocking and intermixing instabilities were observed only at the interfaces of the Ni/Ti pairs, which also showed a more uniform and higher fraction of intermetallics compared to the Ti/Ni pairs in similar spraying conditions. This was attributed to higher degrees of particle/substrate deformation in the Ni/Ti pair. Also, the bond strength of the Ni/Ti pair appeared to be almost three folds of the Ti/Ni pair (64.31 MPa vs. 22.8 MPa). These findings are considered to have implications in cold-spray additive manufacturing of hybrid components or bimetals.