Titanium alloys are used in different industries such as biomedical, aerospace, aeronautic, chemical, and naval. Those industries have high requirements with few damage tolerances. The aim of this work was to study the corrosion behavior of titanium alloys anodizing and non-anodizing in alkaline (KOH and NaOH) solutions, exposed in 3.5%wt. NaCl and 3.5% wt. H2SO4 solutions at room temperature using cyclic potentiodynamic polarization (CPP) according to standards in order to obtain electrochemical parameters as the passivation range (PR), corrosion type, passive layer persistence, corrosion potential (Ecorr), and corrosion rate. The alloy Ti Beta-C anodized presented better corrosion resistance

than Ti-6Al-4V in both media. The smallest corrosion rate is

presented in Beta-C samples (4.72 E-8 A/cm2) and the highest

corrosion rate is CP2 (1.61 E-5 A/cm2

Almeraya Calderón, Facundo

Cabral Miramontes, José Ángel

Díaz Salgado, J. A.

Estupiñan López, F. H.

Gaona Tiburcio, Citlalli

Jáquez Muñoz, Jesús Manuel

Lara Banda, María del Refugio

Martínez Ramos, C.

Zambrano Robledo, Patricia del Carmen

Martínez Ramos, Cynthia

Estupiñan López, Francisco H.

Repositorio Academico Digital UANL

Cyclic Potentiodynamic Polarization On Titanium Alloys Anodizing In Alkaline Solutions J. A. Díaz-Salgado,z C. Gaona, J. M. Jaquez-Muñoz, C. Martínez-Ramos, P. Zambrano-Robledo, M. Lara-Banda, F. Estupiñán-Lopez, F. Almeraya-Calderón, J. A. Cabral-Miramontes a Universidad Autónoma de Nuevo León, Centro de Investigación e Innovación en Ingeniería Aeronáutica, México. Titanium alloys are used in different industries such as biomedical, aerospace, aeronautic, chemical, and naval. Those industries have high requirements with few damage tolerances. The aim of this work was to study the corrosion behavior of titanium alloys anodizing and non-anodizing in alkaline (KOH and NaOH) solutions, exposed in 3.5%wt. NaCl and 3.5% wt. H2SO4 solutions at room temperature using cyclic potentiodynamic polarization (CPP) according to standards in order to obtain electrochemical parameters as the passivation range (PR), corrosion type, passive layer persistence, corrosion potential (Ecorr), and corrosion rate. The alloy Ti Beta-C anodized presented better corrosion resistance than Ti-6Al-4V in both media. The smallest corrosion rate is presented in Beta-C samples (4.72 E-8 A/cm2) and the highest corrosion rate is CP2 (1.61 E-5 A/cm2) Introduction Aeronautic materials have an important role regarding fuel efficiency which also are determined by its mechanical, physical, chemical electrical and thermal properties.  Material density reduction is the most effective way to decrease structural weight and enhance aircraft development. Pure titanium is well known due to its low thermal conductivity, relatively low density and elasticity, moderate stiffness and excellent behavior against corrosion in several environments and reactivity of elements. [11] Nowadays, aluminum is in top of most used materials in aircrafts but recently the use and implementation of titanium and composites is taking more visibility in charts. Titanium replaced materials as steel and several superalloys due to the great difference presented in density and its consequences in fuel savings. For example, Boeing 787 contains around 15% Ti, while past models as Boeing 747 used to show 2.6% and Boeing 777 8.3% of titanium leading to an increase of 40% in last two generations of Boeing Aircrafts T. Fu in 2015, worked with titanium CP2 in a solution of sodium chloride at 3.5% through cyclic Potentiodynamic polarization (CPP), obtaining as results the increase of corrosion resistance when this alloy present a passive layer which difficult the penetration of chlorine ions. [2]A. C. Alves in 2017 evaluating titanium CP2 using CPP and Spectroscopy of Electrochemical Impedance after an anodic treatment observed that chlorine ions struggle more to get inside the material. [3]zE-mail: joel_diza@hotmail.com10.1149/11001.0049ecst ©The Electrochemical SocietyECS Transactions, 110 (1) 49-61 (2023)49Analyzing titanium CP2 in H2SO4 using CPP, Dubent and Mazard obtained corrosion velocities of 20 μm per year being a greater value than inicially expected. [4]L. Zhou in 2019 performed an investigation where they compared titanium alpha (CP),alpha + beta (Ti-6Al-4V) and beta metastable (Ti-13Nb-13Zr) resulting in a tendency tobetter corrosion resistance the closer to beta phase. [5]In 2020 A. Nemtsov and P. Kirshkov studied anodic oxidation in laminates of pure titaniumunder a compilation of solutions (1.5 M sulfuric acid, 0.3 M phosphoric acid and 0.3 M ofhydrogen peroxide) leading to a nanotubes layer with porosity between 40 and 70 nm. [1]Enhancing the electrochemical properties in titanium alloys results in an extension of service lifespan leading to reduction of expenses in aeronautical industry. Titanium alloys are substituting steel alloys of aircraft’s critical components helping to reduce structural weight and saving fuel. The use of alkaline solutions in anodizing process become easier its disposition and reduce environmental damage as acidic solutions. Methodology Experimental Procedure Preparation Specimen preparation consisted in sectioning 16 samples (8 Ti Beta-C and 8 Ti CP2) measuring a thickness of 0.5 cm and then a mechanical cleaning using SiC sandpaper from 80P to 800P before anodizing. Anodizing Process Pretreatment consisted of ultrasonic cleaning in ethanol (C2H5OH) and deionized water. Each of 16 specimens are connected to a circuit controlled by equipment using the following parameters. • Solutions KOH and NaOH at 1M per liter of distilled water.• Input current 0.025 and 0.010 A/cm2.• Duration of 300 and 600 s.Solutions is at room temperature and as energy dissipation it is used circulating water around the container to cool down the system due to exothermal reaction occurring during the process. The specimen is totally submerged in KOH or NaOH a determined time with bubbling. Electrochemical Tests Measurements were conducted at room temperature using a Solartron 1286 potentiostat/galvanostat/ZRA (Zero Resistance Ammeter) in 3.5 wt.% NaCl solution.  A conventional three-electrode cell configuration was used for electrochemical corrosion studies, which consisted of a working electrode, WE (Titanium and its alloys), a ECS Transactions, 110 (1) 49-61 (2023)50  reference electrode, RE (saturated calomel electrode (SCE), and a counter electrode, CE (platinum mesh).  The CPP measurements were conducted over a potential scan range between −1.2 and 1.2 V vs. SCE from corrosion potential (Ecorr), using a scan rate of 1 mV/sec.  Results  Chemical Composition  Alloys used in this investigation showed elements presented in table I, according to supplier information.  TABLE I. Chemical composition of titanium alloys Alloy  Elements (% wt.)  Ti Al V Zr Mo Cr Sn Ti CP2 99.8 -- 0.2 -- -- -- -- Ti Beta-C 75.2 4.2 8.1 4.3 3.9 3.3 --  Electrochemical Characterization  Figure I below present Potentiodynamic Polarization Curves immerged in potassium hydroxide using a current input of 0.010 A/cm2 interacting with NaCl at 3.5% as test solution. This chart show potential (V) vs. ECS against natural logarithm of the current. CP2 alloy present passivation/activation cycles shown as fluctuations.  ECS Transactions, 110 (1) 49-61 (2023)51   Figure 1.  PPC for titanium alloys anodized in KOH using a current density input of 0.010 A/cm2 and exposed in NaCl at 3.5% during the test using 2 different immersion time.  Figure II, below show the behavior of coupons anodized in potassium hydroxide applying 0.025 A/cm2 interacting with NaCl at 3.5% as test solution. This chart show potential (V) vs. ECS against natural logarithm of the current. CP2 alloy present passivation/activation cycles shown as fluctuations.  ECS Transactions, 110 (1) 49-61 (2023)52    Figure II.  PPC for titanium alloys anodized in KOH using a current density input of 0.025 A/cm2 and exposed in NaCl at 3.5% during the test using 2 different immersion time.  Figure III, below show the behavior of coupons anodized in sodium hydroxide applying 0.010 A/cm2 interacting with NaCl at 3.5% as test solution. This chart show potential (V) vs. ECS against natural logarithm of the current. CP2 alloy present passivation/activation cycles shown as fluctuations.  ECS Transactions, 110 (1) 49-61 (2023)53    Figure III.  PPC for titanium alloys anodized in NaOH using a current density input of 0.010 A/cm2 and exposed in NaCl at 3.5% during the test using 2 different immersion time.  Figure IV, below show the behavior of coupons anodized in sodium hydroxide applying 0.025 A/cm2 interacting with NaCl at 3.5% as test solution. This chart show potential (V) vs. ECS against natural logarithm of the current. CP2 alloy present passivation/activation cycles shown as fluctuations.  ECS Transactions, 110 (1) 49-61 (2023)54    Figure IV.  PPC for titanium alloys anodized in NaOH using a current density input of 0.025 A/cm2 and exposed in NaCl at 3.5% during the test using 2 different immersion time.   Table II and III summarize results observed in figures I to IV   ECS Transactions, 110 (1) 49-61 (2023)55   TABLE II.  Summary beta-C alloy Alloy Solution Duration (min) Input (A/cm2) I Corr (A/cm2) E Corr (V) Hysteresis Passivation range (V) Beta-C KOH (1) 10 0.010 4.72 E-8 0.226 Negative 1.426 10 0.025 1.16 E-7 0.285 Negative 1.342 5 0.010 5.29 E-8 0.206 Negative 1.280 5 0.025 3.60 E-7 0.026 Negative 1.478 NaOH (2) 10 0.010 2.72 E-7 0.267 Negative 1.491 10 0.025 1.01 E-6 0.192 Negative 1.543 5 0.010 6.32 E-7 0.050 Negative 1.332 5 0.025 4.04 E-7 0.137 Negative 1.495   The smallest current density is presented in Beta-C sample anodized in potassium hydroxide during 10 minutes using an input current of 0.010 A/cm2 while the greatest current density is shown in sample anodized in sodium hydroxide during 10 minutes with an input current of 0.025 A/cm2. The more and less susceptible to corrosion were anodized using KOH and both with an input of 0.025 A/cm2 being duration of immersion the difference (5 mins and 10 mins respectively). The shortest passivation range is coupon under conditions of potassium hydroxide during 5 minutes with input current of 0.010 A/cm2 and, in the other hand, the longest passivation range is presented in the same iteration as the greatest current density.   ECS Transactions, 110 (1) 49-61 (2023)56  TABLE III.  Summary CP2 alloy Alloy Solution Duration (min) Input (A/cm2) I Corr (A/cm2) E Corr (V) Hysteresis Passivation range (V) CP2 KOH (1) 10 0.010 4.08 E-6 -0.448 Negative 1.551 10 0.025 2.38 E-5 -0.346 Negative 1.756 5 0.010 9.68 E-6 -0.404 Negative 1.375 5 0.025 1.61 E-5 -0.409 Negative 1.438 NaOH (2) 10 0.010 2.23 E-5 -0.500 Negative 1.311 10 0.025 1.67 E-5 -0.514 Negative 1.373 5 0.010 7.38 E-7 -0.431 Negative 1.337 5 0.025 2.75 E-6 -0.479 Negative 1.435   The greatest current density is presented in CP2 sample anodized in potassium hydroxide during 5 minutes using an input current of 0.025 A/cm2 while the smallest current density is shown in sample anodized in sodium hydroxide during 10 minutes with an input current of 0.010 A/cm2. The more and less susceptible to corrosion were anodized with an input of 0.025 A/cm2 and duration of 10 minutes of immersion being the anodizing solution the difference (NaOH and KOH respectively). The longest passivation range is coupon under conditions of potassium hydroxide during 10 minutes with input current of 0.025 A/cm2 and, in the other hand, the shortest passivation range is presented sodium hydroxide during 10 minutes using a current input of 0.010 A/cm2.   SEM analysis  Figure V and VI are superficial metallography of Ti CP2 and beta-C respectively. Ti CP2 present alpha phase matrix while beta-C show beta phase matrix  ECS Transactions, 110 (1) 49-61 (2023)57    Figure V.  Superficial metallography Ti CP2 after anodizing process and electrochemical test.  Figure V present alpha phase expected in Ti alloys CP2 while Figure VI below shows alpha + beta phase expected in Ti alloys beta-C    Figure VI.  Superficial metallography Ti beta-C after anodizing process and electrochemical test   ECS Transactions, 110 (1) 49-61 (2023)58   Conclusions  Summary and interpretation  CP2 tests show noise attributed to activation/passivation cycles.  • CP2 in KOH at 0.010 Amps during 10 mins presents the noisiest performance. • CP2 in NaOH at 0.010 Amps during 5 mins shows cycles after the hysteresis. • CP2 in NaOH at 0.025 Amps during 5 mins displays similar behavior as in 0.010 Amps. Beta-C performed lowest corrosion rate (4.72 E-8 A/cm2) compared to CP2 showing the highest current density (1.61 E-5 A/cm2) meaning a longer lifespan for beta-C sample. Cases considering 0.025 A present lower values of E Corr leading to more susceptibility to corrosion. Combination Beta-C, 10 mins, KOH, 0.010 A shows the lowest density current. In the other hand, iteration CP2, 10 min, KOH, 0.025 A is the highest corrosion kinetics tending to loss more material. In general, CP2 is more susceptible to corrosion (-0.514 V) than Beta-C presenting the lower potentials (0.285 V) in all samples. Specimens of 5 mins immersion are less susceptible to corrosion considering anodic solution and alloy while the E Corr is lower in each iteration. Samples under 0.010 A condition struggle less to get into passivation (1.280 V) and present density current lower than 0.025 A samples.  General conclusion  Service lifespan of beta-C alloy anodized by potassium hydroxide will be longer than CP2 alloy under same conditions due to susceptibility and current density presented in this investigation. Every test presented negative hysteresis leading to uniform corrosion along specimens.   Limitations and Recommendations  Scope of this work was achieved which is compare anodized alloys varying current, duration and alkaline solutions. These results are relevant and part of future researches to compare results using different electrochemical characterization as Electrochemical Impedance Spectroscopy and Electrochemical Noise. Additional to investigation matrix, obtaining results from conventional acidic anodization processes collecting data from same three electrochemical methods.   Acknowledgments  Thanks for sources and tools to UANL-FIME-CIIIA, as well to my teachers for the development of this investigation and to CONACYT for the economical support to make possible this work.   ECS Transactions, 110 (1) 49-61 (2023)59  References  1. Nemtsov, P. Kirshkov, “Electrochemical Characterization of Titanium Oxide Nanoparticle through Anodic Oxidation”, Medbiotech Journal, 4 (2): 083-086, (2020). 2. T. Fu, Z. Zhan, Y. Tang, Z. Liu, J.  Liu, L. Li, X. Yu, “Effect of surface mechanical attrition treatment on corrosion resistance of commercial pure titanium”, Surface & Coatings Technology, Vol. 280, pp. 129-135, (2015). 3. 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Cyclic potentiodynamic polarization on titanium alloys anodizing in alkaline solutions

Cyclic potentiodynamic polarization on titanium alloys anodizing in alkaline solutions

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