Subscriber access provided by UNIV OF SCIENCES PHILADELPHIA
Surfaces, Interfaces, and Applications
Improvement of Corrosion and Tribocorrosion Behavior of Pure Titanium by Sub-Zero Anodic Spark Oxidation Mohammad Fazel, Hamid Reza Salimijazi, and Morteza Shamanian ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b02331 • Publication Date (Web): 06 Apr 2018 Downloaded from http://pubs.acs.org on April 11, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
Improvement of Corrosion and Tribocorrosion Behavior of Pure Titanium by Sub-Zero Anodic Spark Oxidation M. Fazel*, H.R. Salimijazi, M. Shamanian Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran
Abstract The present investigation reports corrosion and tribocorrosion behavior of Anodic Spark Oxidation (ASO) coatings formed at 20oC and -10oC temperatures. Despite the numerous open pores on the 20̊C formed layers, the plasma discharged channels were blocked on the surfaces of the sub-zero ASO coatings. According to polarization curves, the -10oC treated samples showed a significant increase in the corrosion resistance (jcorr of 0.75 nA.cm-2). Electrochemical Impedance Spectroscopy (EIS) experiments illustrated lower capacitance and higher resistance of both inner and porous layers formed at low temperature. Sub-zero ASO coatings also demonstrated the lowest overall open circuit potential (OCP) drop in tribocorrosion studies. Keywords: Anodic Spark Oxidation, Sub-zero ASO coating, Corrosion resistance, Electrochemical Impedance Spectroscopy, Tribocorrosion.
* Corresponding author, Tel.: +989103144002
[email protected] ACS Paragon Plus Environment
ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 24
1. Introduction Titanium and its alloys have been developed in the automotive, aerospace and aviation industries, where the high strength to weight ratio is the primary consideration
1-3
. Addition to,
they have been used in various corrosive environments because of their high corrosion resistance in different aqueous solutions, which is attributed to naturally grown of an adherent, continuous and thin titanium oxide film on the surface
4-6
. Nevertheless, the poor tribological properties of
natural oxide layer cannot guarantee the protection of titanium and its alloys to interact with aggressive surrounding environment
7-10
. Hence, an appropriate surface modification is required
to get an enhanced corrosion and triocorrosion resistance. Anodic spark oxidation (ASO) technique, also known as Micro-arc oxidation (MAO), is a novel, promising and attractive surface engineering method to produce crystalline films with low friction and high wear and corrosion resistance 9-13. The process involves anodic oxidation at potentials above the dielectric breakdown of TiO2 layer, accompanied by the appearance of swarming micro-discharges on the surface 14-15. ASO coatings includes an inner barrier layer occurs in the beginning on the active metal surface and an outer porous layer produced by a dielectric breakdown of ion-conducting film at high potentials
16-17
. Because of a dense and insulating structure, the inner barrier layer can highly
improve the corrosion characteristics. The corrosion resistance of coating is also affected by the outer film properties such as pore size, thickness and surface morphology related to electrochemical parameters 1, 18-19. Choosing of an appropriate electrolyte and incorporation of electrolyte constituents (e.g. phosphorus) into these conversion coatings affects the corrosion behavior. Many authors demonstrated a linear dependency between the anodizing voltage and thickness of the oxide film 20-23
. However, the corrosion resistance of the ASO treated specimens can be decreased by
ACS Paragon Plus Environment
Page 3 of 24 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Applied Materials & Interfaces
increasing the anodic potential 24-25. Electrolyte temperature is another important parameter, which can affect the thickness and properties of the oxide layer. Yetim 10 illustrated that the thickness of the anodic film performed at -3oC (hard anodized samples) was nearly twice higher than those at room temperature. Addition to, the hard anodized samples showed the higher hardness and wear resistance. However, because of the locally high temperature occurs during dielectric breakdown of the oxide film, the influence of decreasing the process temperature has been less considered by the authors. While, according to above explanations, anodic spark oxidation at low and especially sub-zero temperatures would be able to provide significant changes on surface properties, corrosion and wear behavior. Therefore, the main object of this study is to examine the changes in surface characteristics, corrosion and tribocorrosion behavior of pure Ti treated by anodic spark oxidation at 20oC and -10oC temperatures. 2. Experimental 2.1. Materials and surface treatment
A commercially pure titanium sheet (99.4% Ti, 0.5% Al & other-total
