Hot corrosion resistance of Al2O3 nanoparticles reinforced CoNiCrAlY coatings deposited by LPPS and HVOF processes in molten Na2SO4-V2O5 at 850[formula omitted

Abstract

In this research, satellited CoNiCrAlY/nano-Al2O3 feedstocks with 2 and 4 wt% oxide nanoparticles and conventional CoNiCrAlY powder were deposited through the HVOF and LPPS processes on Inconel 738 substrates. The hot corrosion test was done in molten Na2SO4-55wt.%V2O5 salt at 850 °C for 24 h. The microstructure and phase composition of the as-sprayed and corroded coatings were characterized by the FESEM and XRD. The results showed that by adding Al2O3 nanoparticles in the HVOF CoNiCrAlY coatings up to 4 wt%, the porosity increased from 0.6 to 2.7 vol% and the surface roughness increased from 4.4 to 7.1 μm. By adding Al2O3 nanoparticles in the LPPS CoNiCrAlY coatings up to 4 wt%, the porosity increased from 2 to 3.76 vol%, and the surface roughness increased from 6.1 to 7.5 μm. Penetration of corrosive salt in the conventional and composite HVOF coatings, including 2 and 4 wt% nanoparticles, was obtained as 72, 16, and 140 μm, respectively. Penetration of the corrosive species in the conventional and composite LPPS coatings consisting of 2 and 4 wt% nanoparticles was measured as 91, 125, and 170 μm, respectively. The hot corrosion mechanism was basic and acidic fluxing, creating (Co, Ni)2V2O7, Na(AlO2), CoCo2O4, and NiCr2O4 corrosion products.