Chemical leaching is proposed as a method to control porosity in stainless steel HVOF coatings. The leaching behavior is evaluated as a function of the stainless steel 444 and the pore former (Fe 3 Al) volume fractions and particle size distributions. The resulting porous structures are evaluated by optical microscopy. It was observed that the melting degree of the stainless steel splats was an important factor to retain some mechanical integrity after leaching. A discussion is presented to point out possible routes for the improvement of chemical leaching as a methodology for pore control in thermal spray coatings.

Protective coatings with high wear, erosion and corrosion resistance are of great importance in many fields of application and in particular, in the electric power generation sector. In this paper, the HP-HVOF (high-pressure high velocity oxy-fuel) technique is used to produce dense rapidly quenched metal-ceramic nanocomposite protective coatings. The powders for the thermal spray process are produced by high energy ball milling using mechanochemical displacement reactions to synthesize ceramic components in-situ at the nanometric scale. Boron nitride solid lubricant is used as a source of nitrogen and boron to precipitate nitride and boride phases in a corrosion resistant iron aluminide metal matrix. The formation of the hard phases during milling and/or thermal treatments is investigated using various analytical methods. The tribological properties of the coatings with and without ceramic additives are reported.