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

Chemical solution deposition (CSD) methods involving the thermal decomposition of 5.0 M Er(NO 3 ) 3 ·5H 2 O and Y(NO 3 ) 3 ·6H 2 O 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 Er 2 O 3 and Y 2 O 3 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 Er 2 O 3 and Y 2 O 3 .