Objective

1. Characterization of Species and Coating Morphology Involved in the Corrosion Protection of Rare Earth Based Coatings H2O H2O RE2O3 RE(OH)3 RE2O(OH) CO2 CO2 RE2(OH)2(3-x) (CO3)x RE2O2CO3 RE2O3 Commercially available forms RE6O11 Top Coat Non-Chromate Primer Cerium Conversion Coating RE6O11 (cubic) Metallic Substrate RE2O3 (hexagonal-A) More stable form F-15 coated with Deft 02GN084 non-chromate primer that uses a RE-based inhibitor Technician coating an Apache fuselagewith Deft non-chrome primer RE Primer System • Primers containing RE compounds provide corrosion protection to Al alloys but the mechanism is • RE-based primer coatings exhibit the best performance when deposited on Al alloys with chromate conversion coatings (CCC) RE Stability Studies Background • Intensity and nature of H2O and CO2 adsorption (aging) are affected by the preparation and structure of a RE compound • Properties of RE compounds can be altered during aging process • In atmospheric conditions/room temperature • Hexagonal-A RE2O3 becomes hydrated and carbonated in bulk • Cubic RE6O11 becomes hydrated and carbonated at the surface • Environmentally friendly RE compounds are currently being used to replace chromates in military applications • RE phases are not inherently protective but depend on processing parameters and the phases/structures present CeCC System • CeCC can pass 336 hours neutral salt spray testing without exhibiting salt tailing • Critical process parameters will be examined for the CeCC, including the use of a phosphate solution post treatment The guidance and support Bruce Sartwell of SERDP and Donna Ballard of AFRL/ML is gratefully acknowledged. W. Fahrenholtz (PI ), M. O’Keefe (co-PI), W. Pinc, B. Treu, S. Joshi, E. Morris, and R. Albers SERDP Project WP-1618 Objective • This project will investigate the mechanisms by which rare-earth (RE) compounds inhibit corrosion of metallic substrates. Deft 44GN098 scribe area after 500 hours salt spray testing. 5 cm 20 μm Schematic of cerium based conversion coating (CeCC) and proprietary RE inhibitors in epoxy-polyamide primer system. CeCC after 336 hours salt spray testing no salt tails formed but pits observed • The deposition parameters of the CeCC and formulation of the primer coating are known • The protection mechanisms of these two coatings will be examined in order to gain scientific knowledge of the coating system CeCC with no post treatment, after 72 hours salt spray testing CeCC with a post treatment, after 336 hours salt spray testing Representative Al 2024-T3 with a CeCC after 14 days of salt fog. FIB image of the CeCC/aluminum alloy substrate interface.