Thermal Spraying of Nanocrystalline Ni Coatings

Abstract

The present paper describes the synthesis, characterization, and grain growth behavior of nanocrystalline Ni coatings generated using a novel synthesis approach, namely high velocity oxy-fuel (HVOF) thermal spraying. In the present investigation, the feedstock powders were prepared by mechanical milling in a methanol environment which yielded agglomerates with a flake-shaped geometry and an average grain size of less than 100 nm. The milled powders were then introduced into the HVOF spray system in order to investigate the feasibility of generating a coating with grain sizes in the nanocrystalline range (e.g., <100 nm). Scanning electron microscopy and transmission electron microscopy were used to study the morphology of the nanometric particles and the microstructure of the milled powders and the as-sprayed coatings. Transmission electron microscopy analysis performed on cross sections of the coating revealed a mixture of fine nanocrystalline grains and elongated coarse grains.