Chemical Solution Deposition of Protective Er2O3 and Y2O3 Coatings onto Stainless Steel for Molten Metal Casting using Metal-Nitrate Precursors.

Abstract

Chemical solution deposition (CSD) methods involving the thermal decomposition of 5.0 M Er(NO3)3·5H2O and Y(NO3)3·6H2O precursor solutions were employed to fabricate protective erbia and yttria coatings onto stainless steel (SS304/SS316) coupons. The two techniques tested were dip and spray coating, which were then compared to a commercial yttria spray (ZYP Coatings). It was determined that solution concentration, solvent choice, injection of Er2O3 and Y2O3 micropowder, and the annealing temperature/ramp profile were critical to the coatings' physical properties. For dip coatings, thicknesses were 1-20 μm after two dipping/annealing cycles, and adhesion strength was ∼1000 psi, increasing up to ∼1300 psi if the SS coupons had preliminary sandblasting. Spray coatings from precursor solutions were reported to have thicknesses of 20-80 μm and adhesion strength less than 500 psi (regardless of the coupon surface finish). Cross-sectional views of the coatings confirmed subsurface porosity, and XRD results indicated that the coatings were polycrystalline, with patterns typical to that of cubic Er2O3 and Y2O3.