Mathematical modeling of particle behavior of nanocrystalline Ni during high velocity oxy-fuel thermal spray

The present paper describes a mathematical model predicting the particle behavior of nanocrystalline Ni powders during high velocity oxy-fuel (HVOF) spray. The model development was motivated by successful experimental results as described in the following. The feedstock powders were synthesized by mechanical milling to produce flake-shaped agglomerates with an average grain size of less than 100 nm. The powders were then introduced into the HVOF spray to produce a nanocrystalline coating. Scanning electron microscopy and transmission electron microscopy were used to study the morphology of the nanometric particles and the resultant sprayed coatings. The equations describing the momentum and energy transfer coupled with a modified geometric ratio were used to account for the size and morphological effects of the nanometric agglomerates. Particle velocities and temperatures of the numerical calculations indicated that fractions of the agglomerates did not melt during the HVOF spraying process, which concurs with the observed experimental results. (C) 1998 Acta Metallurgica Inc.