Synthesis and mechanical properties of nanocrystalline Ni coatings produced by cold gas dynamic spraying

Nickel powder was mechanically milled in liquid nitrogen to achieve an average nanocrystalline grain size in the range of 20 to 30 nm. The powder was subsequently sprayed using the Cold Gas Dynamic Spraying (CGDS) technology. The resulting coatings were evaluated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and micro- and nanoindentation. XRD and TEM coating analysis show that the nanocrystalline grain structure of the cryomilled feedstock powder was retained. Hardness values of 5.93 GPa (HV300 g) were observed in the deposited nickel coatings and were comparable to electrodeposited nanocrystalline nickel coatings for the same range of grain sizes. The ability to use CGDS to produce nanocrystalline nickel coatings while preserving the feedstock powder microstructure was demonstrated in this work.