Nanoscale characterization of FeAl-HVOF coatings

FeAl intermetallic is one of the highly attractive aluminides due to its high specific properties and good oxidation resistance. The present work investigates the production of iron aluminide coatings obtained by means of the High Velocity Oxygen Fuel process. Two well differentiated structures have been achieved by the modification of particle size distribution, reaching lower oxidation at splat boundaries with particle sizes in the range of 40-60 μm. Such features have been studied by using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) as well. TEM has also been employed to illustrate the grain size and to reveal the degree of the compound ordering in the as-sprayed form; despite rapid solidification being a way to induce disordering in intermetallics, since the feedstock is a Fe-40 at.% Al milled powder, it becomes slightly ordered at the high temperatures during in-flight time. Moreover, a further attempt to study how the order affects to the coating structure, the initial powder was annealed in order to induce such ordering before spraying. While the ordering observed in the as-sprayed milled powder came from the thermal history of particles during the spraying process, the ordering of the as-annealed powder is much more evidenced by the visible superlattice spots.