Microstructural evolution and mechanical, and corrosion property evaluation of Cu–30Ni alloy formed by Direct Metal Deposition process

In the current investigation Cu–30Ni alloy was successfully laser deposited on a rolled C71500 plate substrate by Direct Metal Deposition technology. The microstructural investigation of the clad was performed using optical and scanning electron microscopy. The phase and crystal structure analysis was performed using X-ray diffraction technique and transmission electron microscopy. The microstructure consisted of columnar and equiaxed dendrites with face centered cubic crystal structure. The dendrites grew epitaxially from the substrate and layer and bead boundaries. Dendrites’ growth direction 〈0 0 1〉 and growth angle 60° was maintained in each layer. The average primary dendritic arm spacing at the bottom part of the layers was about 7.5 μm and average secondary dendritic arm spacing in the upper part of the layer varied between 2 μm and 4.5 μm. The lattice parameter of the identified phase was found to be longer than that reported in literature. The reported lattice parameters in literature are however from samples processed under equilibrium conditions. The microhardness of the clad was found to be less than the substrate but very consistent along the clad. Cu–30Ni clad specimen showed higher ultimate tensile strength but lower yield strength and percentage elongation as compared to the C71500 substrate. DMD Cu–30Ni clad/C71500 substrate specimen showed the worst mechanical properties. The corrosion resistance of the specimens was found to decrease in the order DMD Cu–30Ni clad, half-and-half DMD Cu–30Ni clad-C71500 substrate, and C71500 substrate.

Research highlights
► Cu–30Ni alloy was successfully deposited with CO2 laser DMD system on C71500 substrate.
► The microstructure consists of a single solid solution phase.
► Columnar dendrites growing into equiaxed dendrites form layer microstructure.
► Dendrite growth direction and angle relative to substrate was maintained in each layer.
► Lattice parameter of solid solution phase is longer than reported lattice parameters.