Microstructure and Dry-Sliding Behavior of Atmospheric Plasma-Sprayed FeCrAl Coatings Produced at Different Nominal Powder Feed Rates

Atmospheric plasma-sprayed FeCrAl coatings possess heterogeneous lamellar structures whose characterization is important for interpreting friction and wear. This study compared four as-sprayed FeCrAl coatings produced at nominal powder feed rates of 25–40 g/min and a common stand-off distance of 150 mm. The objective was to compare their microstructural and surface characteristics with their room-temperature dry-sliding responses, particularly the correspondence between friction and wear rankings. The coatings were examined using SEM/EDS, X-ray diffraction, cross-sectional image analysis, surface profilometry, instrumented indentation, and ball-on-disk testing. Mean coating thicknesses ranged from 162 to 702 µm, while region-specific apparent porosity estimates ranged from 0.38 to 1.49%. The coatings exhibited heterogeneous lamellar microstructures and broadly similar diffraction patterns dominated by an α-Fe-type bcc matrix containing Cr, with additional reflections assigned to Fe3O4. The mean Ra values ranged from 22.83 ± 0.13 to 26.91 ± 0.36 µm (mean ± SD, n = 3), and individual indentations revealed substantial variation in local mechanical response. F3 exhibited the lowest measured specific wear rate of 1.051 × 10−4 mm3/(N·m) among the tested specimens. F4 showed the lowest approximate post-running-in friction coefficient of 0.77–0.80, whereas F1 exhibited the highest measured specific wear rate of 1.982 × 10−4 mm3/(N·m). Thus, the friction and wear rankings differed, and neither the measured roughness nor the region-specific apparent porosity alone accounted for the wear ranking. These findings characterize the tested specimens; one sliding test per coating and incomplete deposition records preclude establishing reproducibility or attributing the differences exclusively to powder feed rate.