Solute and grain boundary strengthening effects in nanostructured Ni-Co alloys

Nanostructured Nickel and Nickel-Cobalt coatings across the Co composition range of 0-83 wt% were synthesized by electrodeposition. Surface morphology, microstructure, and phase formation were investigated in conjunction with alloying level using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Rietveld refinement. Fine surface morphologies with average roughness of 6-20 nm and estimated grain sizes of 4-30 nm were achieved. The deposit hardness was found to increase with Co addition and reached a maximum value of 584 HV at 43 wt% Co. Further Co addition resulted in phase change and a decrease in hardness despite finer grain sizes of 15 nm and smaller. Although the HCP phase is expected in Co-rich alloys (>55 wt% Co), our results showed that the underlying phase gradually changed from FCC to HCP starting 43 wt % Co. Solid solution strengthening, phase formation, internal stress, and grain boundary strengthening were considered for their roles in Ni-Co alloys. Ni-rich, FCC-based deposits showed improved hardness from solid solution and Hall-Petch strengthening, while Co-rich, HCP-containing deposits did not benefit from the heavily refined grain size.

Automated summary

Nanostructured Nickel and Nickel-Cobalt coatings were synthesized by electrodeposition across the Co composition range of 0-83 wt%. The study investigated the effects of alloying level on surface morphology, microstructure, and phase formation. Results showed an increase in hardness with Co addition, but further Co addition led to phase change and decreased hardness despite smaller grain sizes.