Characteristics Assessment of Thermally Sprayed Hybrid Nano-Composite Layers on T22 Steel

Nickel–chromium (NiCr) and nickel–chromium aluminum (NiCrAl) hybrid nanocomposite coatings reinforced with yttria-stabilized zirconia (YSZ) and silicon carbide (SiC) nanoparticles were deposited on T22 boiler tube steel using the high-velocity oxy-fuel (HVOF) thermal spraying technique. Four coating compositions were developed: NiCr with 10 wt.% YSZ and 5 wt.% SiC, NiCr with 10 wt.% YSZ and 10 wt.% SiC, NiCrAl with 10 wt.% YSZ and 5 wt.% SiC, and NiCrAl with 10 wt.% YSZ and 10 wt.% SiC. The coatings were characterized using field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The results revealed that increasing YSZ and SiC content significantly reduced porosity and enhanced microhardness. Among all the coatings, NiCr reinforced with 10 wt.% YSZ and 10 wt.% SiC exhibited the lowest porosity, most uniform microstructure, and highest hardness due to effective pore filling by nanoparticles.