47 ice | science Nanocrystalline zinc titanate (ZnTiO 3 ) coatings were deposited by atomic layer deposition (ALD) on AISI 52100 steel to study ZnTiO 3 corrosion protection. The main aim of this study was to determine how the coating can inhibit pitting formation of 52100 steel in both saline solution and simulated body fluid (SBF) media. Potentiodynamic polarization tests revealed increasing corrosion potentials for the ALD ZnTiO 3 -coated steel specimens with protective efficiencies of 83 and 73% in saline solution and SBF, respectively. Atomic force microscopy analysis of both the ZnTiO 3 -coated and uncoated steel revealed a high surface potential value for the ZnTiO 3 -coated sample as compared to the uncoated sample with a relatively low surface potential. The corrosion rates for the coated steels in both media were calculated and observed to drop by an order of magnitude. Due to the conformality, homogeneity and density of the ALD ZnTiO 3 coatings, migration of Cl - and OH - ions from the electrolytes were inhibited resulting in the improved corrosion resistance. 1. Introduction High carbon alloy steels with carbon content of about 0·6–0·99% have been widely studied for various applications. For example, AISI 52100 is a high carbon alloy steel that is known for its remarkable properties, such as good wear resistance, high strength (635 MPa tensile strength), high hardness (197 Brinell HB)and relatively high fracture toughness (20 MPa√m) that makes it a material of choice for ball and roller bearings, dies and punches. 1,2 However, in applications such as ball bearings, where corrosion resistance is of importance, the performance of AISI 52100 has been observed to be very poor. 3 This poor corrosion resistance is because during heat treatment the chromium forms CrC precipitates and there is almost no free chromium in the martensitic matrix. Several methods have been used to improve the corrosion resistance of this steel, which includes the application of corrosion protection coatings deposited by various techniques such as physical vapor deposition methods 4,5 and sol-gel processing. 6,7 The coatings synthesized by these methods are usually of lower quality; for example, higher porosity resulting in ineffective sealing of the substrates thereby inhibiting the ability to provide quality corrosion resistance. Atomic layer deposition (ALD) is a unique type of chemical vapor deposition technique that is used to deposit elements, binary and ternary compounds and more recently quaternary compounds. As a chemical vapor phase coating deposition method, ALD is entirely based on alternate, self-limiting surface reactions. 8 A typical ALD process involves a sequence of alternate precursor pulsing into a reaction chamber followed by argon or nitrogen purging of the unreacted species or by-products. For every precursor pulsing/ exposure step, the substrate surface is saturated with a monolayer of that precursor thus resulting in self-limiting growth. Due to these unique features, alternate precursor pulsing, self-limiting reactions and separated reactions by purging, ALD results in very high coating conformality and uniformity with an excellent control of coating thickness thereby providing effective sealing of the underlying substrate. The ability to coat sharp and buried interfaces, deposit multilayer and alloy structures and low temperature processing are further attributes of ALD. 8,9,10,11,12,13 Most ceramic materials inherently exhibit high resistance to oxidation and therefore are very good candidate materials for corrosion protection. Many oxide ceramics grown by different methods have been considered for corrosion resistance. However, only a few reports have been documented for ALD coatings. The irst ALD grown oxide nanolaminate coating for corrosion resistance was reported by Matero et al., 14 who studied the corrosion protection of stainless steel with TiO 2 , Al 2 O 3 , Ta 2 O 5 and Al 2 O 3 -TiO 2 nanolaminates. More recently, ALD grown Al 2 O 3 -Ta 2 O 5 nanolaminates deposited on steel were also studied for corrosion resistance. 3 The major aim of this study was to investigate the corrosion resistance of ALD nanocrystalline ZnTiO 3 coatings on AISI 52100 Nanocrystalline zinc titanate coatings for corrosion protection Ageh, Rajamure, Ho and Scharf ICE Publishing: All rights reserved Keywords: atomic layer deposition/coatings/corrosion/ nanostructures/oxides/pitting/thin films *Corresponding author e-mail address: scharf@unt.edu Victor Ageh BSc Graduate student, Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA Ravi Rajamure BSc Graduate student, Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA Yee H. Ho BSc Graduate student, Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA Thomas W. Scharf PhD* Professor, Department of Materials Science and Engineering, University of North Texas, Denton, TX, USA Nanocrystalline zinc titanate coatings for corrosion protection Nanomaterials and Energy Volume 3 Issue NME2 Pages 47–52 http://dx.doi.org/10.1680/nme.13.00029 Research Article Received 13/11/2013 Accepted 03/01/2014 Published online 07/01/2014