THERMAL SPRAYING OF NANOCRYSTALLINE NI COATINGS

The present paper describes the synthesis, characterization, and grain growth behavior of nanocrystalline Ni coatings generated using: a nov el synthesis approach, namely high velocity oxy-fuel (HVOF) thermal sp raying. In the present investigation, the feedstock powders were prepa red by mechanical milling in a methanol environment which yielded aggl omerates with a flake-shaped geometry and an average grain size of les s than 100 nm. The milled powders were then introduced into the HVOF s pray system in order to investigate the feasibility of generating a co ating with grain sizes in the nanocrystalline range (e.g., <100 nm). S canning electron microscopy and transmission electron microscopy were used to study the morphology of tie nanometric particles and the micro structure of the milled powders and the as-sprayed coatings. Transmiss ion electron microscopy analysis performed on cross sections of the co ating revealed a mixture of fine nanocrystalline grains and elongated coarse grains.