Microstructural evolution of the rapidly quenched Fe–Cr–B alloy thermal spray coatings

The microstructural development of Fe–Cr–B alloy thermal sprayings has been investigated by transmission electron microscopy (TEM), Auger electron spectroscopy and energy dispersive X-ray microanalysis. The Fe–Cr–B alloy powder was composed of both Cr-rich boride phases, such as Cr1.65Fe0.35B0.96 and Cr2B, and α-(Fe,Cr) solid solution phase of b.c.c. structure. The boride particles dissolved thermally during the thermal spraying process, resulting in the supersaturation of boron within the nanocrystalline α-(Fe,Cr) solid solution phase. Cross-sectional TEM observation for the sprayed coating layer revealed volume nucleation within a splat and the formation of FeCr2O4 oxide. These can contribute to the evolution of an equiaxed nanocrystalline α-(Fe,Cr) phase.