Mechanically induced grain refinement, recovery and recrystallization of cold-sprayed iron aluminide coatings

FeAl coatings can be processed by cold spraying conditions only under the use of well-tuned parameter sets that guarantee shock-loading conditions, which provide sufficient ductility in iron aluminide intermetallic compounds and are capable to ensure sufficient heat creation and thus thermally softened interfaces for bonding. Original microstructures, present in the powder feedstock particles, locally change under the respectively applied loads and temperatures. Given the challenge due to the anomaly softening of such ordered alloys, the present study describes and discusses the differences of coating microstructures in terms of the effect of spraying parameters such as particle size, gas pressure, spraying distance and substrate heating. Electron backscatter diffraction analysis provides elucidation on the grain refinement mechanisms and internal particle strain upon particle impact. The microstructural characterization is complemented by the misorientation analysis within single grains, which is correlated with the spraying parameters and the respective thermal energy input. The misorientation analysis allows for analyzing grain refinement, internal grain bending and for elucidating associated stress relief mechanisms. The results show that the cold spray deposition of FeAl intermetallics can be explained by mechanically induced adiabatic shear instabilities as well as different recovery and recrystallization mechanisms causing a local stress relief.