Corrosion Protection of Steel with Oxide Nanolaminates Grown by Atomic Layer Deposition

Abstract

Atomic layer deposited (ALD) aluminum and tantalum oxide (Al2O3 and Ta2O5) and their nanolaminates were applied as corrosion protection coatings on AISI 52100 steel. The aim was to combine the good sealing properties of Al2O3 with the chemical stability of Ta2O5 and to optimize the coating architecture in order to obtain the best possible long-term durability. Coating composition and morphology were studied with time-of-flight elastic recoil detection analysis (ToF-ERDA), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission scanning electron microscopy (FESEM) and energy dispersive x-ray spectrometry (EDS). Electrochemical properties were studied with voltammetry and electrochemical impedance spectroscopy (EIS), and corrosion durability with neutral salt spray (NSS) testing. The coatings were observed to be conformal and uniform over rough surfaces, and contained some carbon and hydrogen as impurities. The electrochemical results showed that the Al2O3 coating had superior sealing properties compared to the Ta2O5 coating, and nanolaminates had properties in between those of Al2O3 and Ta2O5. However, in the NSS test the laminate-coated samples survived the best demonstrating long-term durability. Analysis of the laminate structure showed that for 40 and 80 nm laminates the best protection was achieved with 10 and 20 nm layers, respectively.