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Leque, NicholasDevelopment of an Experimental Methodology for Evaluation of Gear Contact Fatigue under High-Power and High-Temperature Conditions
Master of Science, The Ohio State University, 2011, Mechanical Engineering
Contact fatigue failures in the form of pitting or micro-pitting have been a perennial problem in power transmission applications. These failures are dictated by a large number of parameters including loading conditions, gear geometry and tooth modifications, kinematics (rolling and sliding velocities), lubricant parameters (viscosity, pressure-viscosity behavior), and material parameters (material type, hardness, case depth, residual stresses). As such, theoretical treatment of contact fatigue failures has been rather challenging, directing the focus to the experimental investigation of the problem. Most of the experimental gear pitting studies to date were limited to low-speed and low-temperature operating conditions. This study aims at developing a methodology for evaluating the contact fatigue lives of gears under high-speed (pitch-line velocities up to 50 m/s), high-stress (contact stresses up to 2 GPa) and high-temperature (oil inlet temperatures up to 150C). Specifications of a test machine concept that meets these requirements are defined and two test machines are designed and procured for this purpose. Gear test specimens that result in pits consistently are developed with the other competing failures (wear, scuffing, tooth breakage), as well as the high vibration conditions, avoided. Preliminary high-speed tests are presented at the end, representing both automotive and aerospace conditions to show that pitting and micro-pitting failures can be produced with the proposed methodology.

Committee:

Ahmet Kahraman, PhD (Advisor); Carlos Castro, PhD (Committee Member)

Subjects:

Engineering; Mechanical Engineering

Keywords:

Gears; fatigue life; pitting; micro-pitting; high-speed; high-temperature; aerospace; automotive

Workman, MichaelOn Probabilistic Transition Rates Used in Markov Models for Pitting Corrosion
Master of Science, University of Akron, 2014, Applied Mathematics
A stochastic initiation and propagation model is developed to predict the effects of pitting corrosion on susceptible metals. The model relies upon an inhomogeneous Markov chain system in order to describe the propagation of pit depths throughout a discretized set of states. This work mainly examines the flexibility of the model with respect to the probabilistic transition rates λi used in the Markov system. Depending on the form of λi, either an analytical or a numerical solution procedure can be used to solve the Markov system, with the numerical form of λi being able to simulate a wider variety of systems, especially for dynamically changing environments. By modifying the expression of λi, increases or decreases, cyclical changes, or abrupt shifts in environmental corrosivity are studied. Simplifications to the model are also suggested for the sake of computational efficiency. A tool in the form of a Mathematica Computational Document is offered as an example of the model's possible use in industry. Additionally, suggestions are made in regard to metastable pitting and situations where the metal begins in a corroded state. The model is flexible enough to handle these scenarios as long as appropriate data is available.

Committee:

Nao Mimoto, Dr. (Advisor); Curtis Clemons, Dr. (Advisor); Kevin Kreider, Dr. (Advisor); Gerald Young, Dr. (Advisor)

Subjects:

Applied Mathematics

Keywords:

Markov; Markov system; pitting; pitting corrosion; environment; growth rate; cdf; model; prediction; stochastic

Wong, FariatyThe Effect of Alloy Composition on the Localized Corrosion Behavior of Ni-Cr-Mo Alloys
Doctor of Philosophy, The Ohio State University, 2009, Materials Science and Engineering

Ni-Cr-Mo alloy are known as one of the most versatile Ni-based alloys in resisting corrosion. Additions of Cr and Mo have been proven to be the cause of the good corrosion resistance behavior. The role of Cr and Mo in resisting localized corrosion particularly, pitting corrosion was studied. Ni-Cr-Mo alloys were fabricated with twenty four unique compositions. Polarization experiments were conducted on these alloys in 0.5M NaCl and low pH chloride solution at varying temperatures from 45 to 90°C to obtain corrosion parameters namely, pitting and repassivation potentials. Multiple linear regression analysis was performed to construct a mathematical expression that correlate the pitting and repassivation potentials to the alloying content at each environment. This expression allows us to roughly predict the corrosion behavior of the Ni-Cr-Mo alloys through Cr and Mo contents only. It appears that Cr content is more dominant than Mo content in raising the pitting potential in neutral chloride condition. The effect of both Cr and Mo are quite uniform in affecting the repassivation potential values of the alloys in neutral chloride. The effect of Mo is greater than Cr in the low pH and higher temperature solutions in affecting both pitting and repassivation potentials.

Pitting corrosion is commonly preceded by the occurrence of metastable pitting. Thus, one can better understand the pitting process of an alloy through its metastable pitting behavior. Rigorous metastable pitting study was conducted on Ni-Cr-Mo alloys with Cr content varying from 20 to 29 wt.% and Mo content varying from 12 to 25 wt.%. Potentiostatic experiments were performed in 90°C of 0.5M NaCl to promote the metastable pitting incidence. Analysis was done on the potentiostatic data to better characterize the metastable pitting behavior of the Ni-Cr-Mo alloys. It was observed that a higher Mo content in the Ni-based alloy is responsible for the lower peak current values and slowing down the growth rates of the faster growing pits. The Cr content seems to impact the repassivation rates of the metastable pits where higher Cr content increases the repassivation rates.

The repassivation behavior of Ni-Cr-Mo alloys was studied through an electrochemical testing consisted of potentiodynamic-galvanostatic-potentiodynamic polarizations. It was found that higher Mo-containing alloys were extremely corrosion resistant given that they had Cr content of at least 20 wt.%. Alloys with higher Cr and higher Ni content had higher repassivation potentials when compared to another alloy with similar Mo content. Voltage component analysis found surface overpotential and reversible potentials of the alloys determined the repassivation potential values. The crevice growth rate of Alloy C-22 was ohmically controlled. XPS analysis found that Cr(III) oxide was the main passivating element for the Ni-Cr-Mo alloys. Mo(VI) was enriched on the crevice area. Mo in 0, +4, and +6 oxidation states were detected on the transpassive dissolution layers that formed on higher Cr and Mo-containing alloys. Cr(III) hydroxide peak was seen on the crevice site and on the transpassive dissolution layers. Ni elemental peak was observed on highest Cr and highest Mo-containing alloys only.

Committee:

Rudolph Buchheit, Prof. (Advisor); Gerald Frankel, Prof. (Committee Member); John Morral, Prof. (Committee Member)

Subjects:

Materials Science

Keywords:

pitting corrosion; repassivation potential; metastable pitting; alloy composition; Ni alloys

Kim, YoungseokCharacterizations of alloying Cu effect on electrochemical reactions of Al-Cu solid solution alloys
Doctor of Philosophy, The Ohio State University, 2006, Materials Science and Engineering
Copper is a major alloying element for high strength aluminum alloys used in the aerospace industry and is known to have a detrimental effect on localized corrosion. Interplay between Cu-bearing intermetallic particles and the matrix containing at least 1.0 wt % solid solution copper is known to induce pit initiation. But Cu additions to aluminum decrease susceptibility to pit initiation provided that Cu is retained in solid solution. In this study, we show that stimulating alloy dissolution without inducing passive film breakdown significantly ennobles the subsequently measured pitting potential of Al-Cu solid solution alloys. Similar effects are not observed with high purity Al or Al-Zn solid solution alloys. To further investigate the ennobling effect of Cu, metastable pits on high purity Al and Al-Cu solid solution alloys have been examined in detail. Results show that Cu additions decrease the probability of stable pit formation by decreasing metastable pit initiation and growth rates. Surface characterization by scanning transmission electron microscopy and spectral imaging of specially prepared Al-Cu needle-type samples show that Cu is readily enriched at the alloy interface by a range of exposure regimens including those that induce pitting. These results suggest the possibility of local Cu enrichment at incipient pit sites by metastable pitting, which causes ennoblement of the critical pitting potential. In the last part of the study, dissolution kinetics of high purity Al, Al-Mg, and Al-Mg-Cu solid solution alloys are investigated by using an artificial pit electrode cell. It has been determined that Cu ennobles dissolution kinetics of artificial pits for Al-Mg-Cu solid solution.

Committee:

Rudolph Buchheit (Advisor)

Keywords:

aluminu; copper; pitting; TEM; metastable pitting

Franzen, Justin MichaelContact Fatigue Evaluation of Ground and Chemically Polished Spur Gears Made of AISI 4118 Alloy Steel
Master of Science, The Ohio State University, 2013, Mechanical Engineering
In this study, contact fatigue lives of spur gears made of AISI 4118 gear steel are evaluated. Two variations of spur gear specimens are fabricated, one having hard-ground tooth surfaces and one having significantly smoother surfaces achieved by applying a commercial chemical polishing process to the same ground gear specimens. A family of FZG type back-to-back gear test machines is employed to collect macro-pitting (spalling) life data at different contact stress levels for both variations. The resultant statistically determined stress-life curves for ground and chemically surfaces are compared to quantify the increases in pitting life achieved through reductions in surface roughness amplitudes. In addition , the ground gear stress-life curve for 4118 material is compared to ground gear stress-life curve for AISI 4620M material from an earlier study to determine the effect material type on the resultant fatigue lives.

Committee:

Ahmet Kahraman (Advisor); Dennis Guenther (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

gear; pitting; surface fatigue; surface roughness;

Neeley, AlexandraCharacterizing the Localized Corrosion of AA7075-T6 and AA2024-T3 by Optical Profilometry
Master of Science, The Ohio State University, 2012, Materials Science and Engineering
The objective of this work was to use optical profilometry to extend methods of characterizing localized corrosion damage accumulation to support the development of both better predictive models and mechanistic understanding. In regards to predictive models, previous accelerated corrosion testing has shown weak correlations to field exposures. The first part of this work characterized pit distributions for bare AA2024 coupons from atmospheric exposures ranging from sub-tropical beach to desert climates (3-12 months). Three lab exposures (static immersion, ASTM B117, GMW 14872) were also evaluated for AA2024 and AA7075 with a range of three pretreatments (bare, deoxidized, and chromate conversion coated) over 1-7 days. Both field and lab exposures generated maximum pit depths that 10 and 4 times faster than average pit depths, respectively. The difference in pit depths is thought to arise from the occurrence of early pit death and/or delayed pit birth. Cumulative distribution functions revealed notable variation at pit depths greater than the 99th percentile, often characterized by a 'tail' in the distribution. Meaningful interpretation of pit growth kinetics using these pits was not possible. Distributions of pit depth, diameter, and density from atmospheric exposures were compared to those of bare AA2024 lab exposures, generating acceleration factors using a power law fitting approach. Acceleration factors were generally greatest for GMW 14872, followed by ASTM B117 and static immersion, and usually increased with pit depth. Results suggest that the 95th percentile may be the best compromise for eliminating distribution tails while maintaining the focus on the deepest pits. The second part of this work explored optical profilometry in regards to developing a better understanding of the mechanism behind localized cathodic corrosion, following up on the work of Leclere. Pit depth distributions were characterized for AA2024 and AA7075, exposed by static immersion in dilute chloride solutions with and without borate buffer. The presence of buffer yielded less circumferential trenching, typically associated with cathodic corrosion. However, there were no significant differences in pit geometry between buffered and unbuffered exposure solutions. The most notable distinction was that the buffer drastically reduced pit number density, acting more in suppressing nucleation sites than altering pit growth kinetics. Both lifetime prediction modeling and mechanistic studies revealed challenges in monitoring other corrosion modes that may be occurring simultaneously, such as uniform corrosion, subsurface pitting, surface roughness, and pit coalescence. Although optical profilometry revealed complexity of localized corrosion in high strength Al alloys, it does appear to compliment traditional electrochemical techniques that do not consistently discriminate damage accumulation.

Committee:

Rudolph Buchheit, PhD (Advisor); Gerald Frankel, PhD (Other)

Subjects:

Materials Science

Keywords:

corrosion; optical profilometry; aluminum alloy; topography; localized corrosion; cathodic corrosion; pitting; borate; accelerated testing

Brown, Bruce N.The Influence of Sulfides on Localized Corrosion of Mild Steel
Doctor of Philosophy (PhD), Ohio University, 2013, Chemical Engineering (Engineering and Technology)
Understanding the mechanisms that lead to localized corrosion in oil and gas pipeline is of great interest to corrosion engineers worldwide. The objective of this study is to examine the phenomena of localized corrosion in upstream oil and gas industry pipelines which operate under slightly sour conditions due to an H2S/CO2 environment. Experimental studies have been carried out to identify the parameters with the most influence on the likelihood of localized corrosion. It is shown that the solution bulk pH, concentrations of carbonates, concentration of sulfides, and the ionic strength of the solution are the major factors for localized corrosion. The flow temperature, and saturation values for both iron sulfide and iron carbonate were also identified as important parameters affecting the corrosion process. The experimental data were then analyzed and used to develop a correlation to relate these parameters to the likelihood of localized corrosion in mild steel pipelines.

Committee:

Khairul Alam (Advisor); Frank Kraft (Committee Member); Valerie Young (Committee Member); Dina Lopez (Committee Member); Michael Jensen (Committee Member)

Subjects:

Chemical Engineering

Keywords:

localized corrosion; hydrogen sulfide; H2S; carbon dioxide; CO2; pitting; iron sulfide; iron carbonate; corrosion model

Huang, I-Wen EvanUniform Corrosion and General Dissolution of Aluminum Alloys 2024-T3, 6061-T6, and 7075-T6
Doctor of Philosophy, The Ohio State University, 2016, Materials Science and Engineering
Uniform corrosion and general dissolution of aluminum alloys was not as well-studied in the past, although it was known for causing significant amount of weight loss. This work comprises four chapters to understand uniform corrosion of aluminum alloys 2024-T3, 6061-T6, and 7075-T6. A preliminary weight loss experiment was performed for distinguishing corrosion induced weight loss attributed to uniform corrosion and pitting corrosion. The result suggested that uniform corrosion generated a greater mass loss than pitting corrosion. First, to understand uniform corrosion mechanism and kinetics in different environments, a series of static immersion tests in NaCl solutions were performed to provide quantitative measurement of uniform corrosion. Thereafter, uniform corrosion development as a function of temperature, pH, Cl-, and time was investigated to understand the influence of environmental factors. Faster uniform corrosion rate has been found at lower temperature (20 and 40°C) than at higher temperature (60 and 80°C) due to accelerated corrosion product formation at high temperatures inhibiting corrosion reactions. Electrochemical tests including along with scanning electron microscopy (SEM) were utilized to study the temperature effect. Second, in order to further understand the uniform corrosion influence on pit growth kinetics, a long term exposures for 180 days in both immersion and ASTM-B117 test were performed. Uniform corrosion induced surface recession was found to have limited impact on pit geometry regardless of exposure methods. It was also found that the competition for limited cathodic current from uniform corrosion the primary rate limiting factor for pit growth. Very large pits were found after uniform corrosion growth reached a plateau due to corrosion product coverage. Also, optical microscopy and focused ion beam (FIB) imaging has provided more insights of distinctive pitting geometry and subsurface damages found from immersion samples and B117 samples. Although uniform corrosion was studied in various electrolytes, the pH impact was still difficult to discern due to ongoing cathodic reactions that changed electrolyte pH with time. Therefore, buffered pH electrolytes with pH values of 3, 5, 8, and 10 were prepared static immersion tests. Electrochemical experiments were performed in each buffered pH conditions for understanding corrosion mechanisms. Uniform corrosion was found exhibiting higher corrosion rate in buffered acidic and alkaline electrolytes due to pH- and temperature-dependent corrosion product precipitation. Observations were supported by electrochemical, SEM, and EDS observations. Due to the complexity of corrosion data, a reliable corrosion prediction based on empirical observations could be challenging. Artificial neural network (ANN) modeling was used for corrosion data pattern recognition by mimicking human neural network systems. Predictive models were developed based on corrosion data acquired in this study. The model was adaptable through iteratively update its prediction by error minimization during the training phase. Trained ANN model can predict uniform corrosion successfully. In addition to ANN, fuzzy curve analysis was utilized to rank the influence of each input (temperature, pH, Cl-, and time). For example, temperature and pH were found to be the most influential parameters to uniform corrosion. This information can provide feedback for ANN improvement, also known as “data pruning”.

Committee:

Rudolph Buchheit (Advisor); Gerald Frankel (Committee Member); Jenifer Locke (Committee Member); Christopher Taylor (Committee Member)

Subjects:

Engineering; Materials Science; Metallurgy

Keywords:

uniform corrosion, pitting, aluminum alloys, artificial neural network

Moss, Jeremy CA Comparative Study of the Impact of Dip and Jet Lubrication Methods on Spur Gear Contact Fatigue and Efficiency
Master of Science, The Ohio State University, 2016, Mechanical Engineering
An experimental investigation of spur gear efficiency is conducted under various jet-lubricated and dip-lubricated conditions. A test methodology is developed to measure load-independent (spin) and load-dependent (mechanical) losses to a gearbox containing a single spur gear pair. An experimental test matrix is defined to study the influence that the lubrication method has on these losses. The test matrix includes two dip-lubricated conditions that vary in submersion level of the gear pair, and four jet-lubricated conditions that vary in the gear mesh target location and velocity of the oil. Results indicate that the spin power losses are impacted by the lubrication method significantly while the mechanical losses are not influenced. An investigation of spur gear contact fatigue is conducted under several lubrication schemes from the efficiency study. A test methodology is developed to evaluate variations in tooth geometry due to surface wear, roughness, and pitting life. Pitting lives under each lubrication method are analyzed statistically to quantify any meaningful differences in gear pitting life. Results indicate that contact fatigue lives from jet-lubricated tests are as high as dip-lubricated ones as long as jet velocities are sufficient.

Committee:

Ahmet Kahraman, Dr. (Advisor); Brian Harper, Dr. (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Spur Gear; Efficiency; Pitting; Jet Lubrication; Fatigue;

Stalker, Kathryn MIllustrating pit initiation and evolution in aluminum alloys according the a 3-dimensional cellular automata based model
Master of Science, University of Akron, 2016, Applied Mathematics
The objective of this work is to develop a cellular automata based model of pitting initiation and subsequent three-dimensional evolution of pit shapes. Here, a cellular automaton is a collection of cells, each of which may be in one of two states, metallic or electrolyte, arranged over a grid. Pit initiation is implemented over a 2-dimensional grid representative of the metal surface while pit propagation is resolved over a 3-dimensional grid which describes a subsection of the bulk metal. The size of the bulk metal will be on the order of millimeters, and a layer of electrolyte, in which chloride will act as the aggressive anion, will cover the bulk metal. A cell within the automaton may change its state each fixed time interval based on a set of rules, called transition rules. The rules are based upon corrosion mechanisms and are implemented stochastically. Further, parametric analyses are performed to simulate pit damage evolution for a metal electrode in various environments. Results from the model are representative of aluminum alloys relevant to aircraft structures. The initiation scheme is capable of reproducing the number of (meta)stable pitting events per area found in the literature for Aluminum Alloy 7075, and the propagation scheme simulates pit shapes seen in nature, such as subsurface and undercutting pits.

Committee:

Nao Mimoto (Advisor); Curtis Clemons (Committee Member); Kevin Kreider (Committee Member); Gerald Young (Committee Member)

Subjects:

Applied Mathematics

Keywords:

pitting; corrosion; cellular automata

Milliren, Matthew BrittAn Experimental Investigation of the Influence of Various Gear Steels on the Contact Fatigue Lives of Hard Ground Spur Gears
Master of Science, The Ohio State University, 2011, Mechanical Engineering
In this study, the influence of different gear steels on the contact fatigue life of ground spur gear pairs was investigated. The three gear steels considered in the study were (i) AISI 8620, (ii) AISI 4620M, and (iii) AISI 5120M. Batches of gears made out of these three materials using the same finishing process at about the same roughness and hardness levels were used in these tests. Each specimen was qualified for its dimensional accuracy, hardness and surface roughness amplitudes before being tested on standard, FZG type, four-square test machines according to well-defined procedures and failure criteria. Interim inspections throughout each test were used to describe the mechanisms leading to pitting failures. The pitting data obtained for each gear material were tabulated and analyzed statistically whenever possible. The pitting fatigue life results of ground gears made of these materials were compared to each other as well as to baseline shaved gear and super-finished gear data obtained in previous related studies. The results indicated that hard grinding gears increases the pitting life of spur gears substantially in comparison to a baseline of shaved gears. Ground gears were also shown to provide improvements in the same order as super-finished gears.

Committee:

Ahmet Kahraman, PhD (Advisor); Donald Houser, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

spur gear pitting

Huang, JinMechanistic Study of Under Deposit Corrosion of Mild Steel in Aqueous Carbon Dioxide Solution
Doctor of Philosophy (PhD), Ohio University, 2013, Chemical Engineering (Engineering and Technology)
Silica sand is produced from geological formations that contain hydrocarbons and has the potential to be transported with extracted oil and gas along pipeline transmission systems. Consequently, the presence of sand is a significant challenge to production in the oil and gas industry. A particular threat is so called under deposit corrosion, which is refers to accelerated corrosion processes that develop underneath the deposit. Such accelerated corrosion processes may cause leakage of pipelines or result in catastrophic failure without control and prevention. Therefore, it is important to understand the mechanisms of under deposit corrosion. In this dissertation, possible mechanisms of CO2 corrosion of mild steel under sand deposits are proposed and evaluated. Both uniform corrosion processes and localized corrosion were studied. Electrochemical experiments were conducted with and without corrosion inhibitor to examine the effect of silica sand deposits on CO2 corrosion of mild steel. A simple and reliable method for testing of localized under deposit corrosion was developed and verified. It was established that in a solution free of corrosion inhibitor, both anodic and cathodic reactions are retarded by the sand deposit. The presence of the sand also caused a water chemistry difference between deposit covered areas and adjacent uncovered surface regions. This water chemistry difference resulted in a higher solution pH on the steel surface and promoted iron carbonate formation, which acted as a further mass transfer barrier for diffusion. A mechanistic electrochemical model was developed which was able to capture the characteristic features of the effect of sand deposits and was capable of predicting the under deposit corrosion rate. In the study of under deposit corrosion in inhibited environments, three uniform corrosion inhibitors were tested. The effects of environmental factors such as pH and temperature in conjunction with deposit particle size and porosity on inhibition were evaluated. The effect of sand deposit on inhibition mechanisms of different types of corrosion inhibitors were proposed and examined. It was found that general depletion of surfactant inhibitor (imidazoline type) by adsorption on the silica sand surface was not the critical factor that causes inhibition failure in under deposit CO2 corrosion. Slow diffusion of inhibitor through the porous sand deposit layer was also not the limiting factor in cases where inhibition failed. Localized corrosion in the form of pitting was identified in under deposit corrosion and related to the inability of the inhibitor to protect the steel surface in the crevices immediately underneath individual sand particles. These pits rapidly propagated due to galvanic effects, eventually merging and causing a high rate of attack underneath sand deposits.

Committee:

Srdjan Nesic (Advisor); Michael Prudich (Committee Member); Kevin Crist (Committee Member); Howard Dewald (Committee Chair); Michael Jensen (Committee Co-Chair)

Subjects:

Chemical Engineering

Keywords:

CO2 Corrosion; pipeline; under deposit; silica sand; mechanisms; localized corrosion; pitting; corrosion inhibitor; imidazoline; thiosulfate

Klein, Mark AndrewAn Experimental Investigation of Materials and Surface Treatments on Gear contact Fatigue Life
Master of Science, The Ohio State University, 2009, Mechanical Engineering

This study consists of experimental studies involving two modes of gear contact fatigue failure: gear pitting (spalling) and gear scuffing. For pitting studies, several materials and surface treatments were investigated at various stress levels. These surface treatments included (i) hobbed and shaved (baseline), (ii) chemically polished, (iii) shot peened and plastic honed, and (iv) ground gears. Pitting fatigue lives of chemically polished gears were greater than those of baseline specimens. Both shot peened and plastic honed gears and ground gears were shown to have greater pitting fatigue lives than baseline gears. The improved pitting fatigue life of ground gears over baseline gears appears related to the improved involute profile shapes of the specimens.

For gear scuffing experiments, the standard ISO 14635-1 FZG Scuffing Test was performed on AISI 8620 type A spur gears. These experiments included four uncoated gear pairs and one gear pair coated with an experimental PVD coating. Uncoated gears encountered scuffing during Stages 11 and 12. A high correlation between temperature and scuffing results was detected for both coated and uncoated specimens.

Committee:

Ahmet Kahraman, PhD (Advisor); Donald Houser, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

gear; scuffing; spalling; pitting; fatigue contact; spur gears; FZG;

Olson, Garrett WestonExperiments on the High-Power and High-Temperature Performance of Gear Contacts
Master of Science, The Ohio State University, 2012, Mechanical Engineering
In this study, gear contact tests were performed using a recently developed test methodology capable of both high-power (pitch-line velocities up to 50 m/s and pinion torques up to 450 N-m) and high-temperature (oil inlet temperatures up to 150C) operating conditions. Test specimens and operating conditions were chosen in order to simulate high-power automotive and aerospace applications. Automotive test specimens were made from a typical automotive transmission gear steel, SAE 4118M, at surface roughnesses typical of hard ground gears. Aerospace test specimens were made out of a high performance (high-temperature) proprietary gear steel. These aerospace specimens were either chemically polished or super-finished following grinding to achieve roughness amplitudes more than 10 times smoother than typical ground surfaces. Throughout each test interim inspections were used to identify and monitor failure modes. Experimental testing for automotive applications is shown to consistently produce contact fatigue failures in the form of micro-pitting and macro-pitting. Tests were suspended when macro-pits exceeded the test methodologies pre-determined failure criteria. Experimental testing for aerospace applications is shown to be absent of any contact fatigue failures due to the extremely smooth contact surfaces. The primary mode of contact failure in aerospace tests is observed to be scuffing.

Committee:

Ahmet Kahraman (Advisor); Gary Kinzel (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Automotive Engineering; Automotive Materials; Engineering; Mechanical Engineering

Keywords:

gears; gear contacts; high-power; high-temperature; contact fatigue; pitting; scuffing

Whitehead, Timothy DanielFactors influencing pitting and cracking resistance AISI type 420 stainless steel in CO 2environments
Master of Science (MS), Ohio University, 1984, Chemical Engineering (Engineering)

The factors affecting pitting and cracking resistance of Type 420SS in CO 2environments are investigated. These include chloride concentration, pH, temperature, and presence of H 2S.

Potentiostatic polarization curves were used to study pitting, and constant applied potential, step stress, tensile tests were used to investigate the SSC phenomenon. The test environments were NaOH solutions saturated with CO 2.

It is found that the total bicarbonate and chloride concentrations are the two important factors controlling whether pitting will occur. The presence of small amounts of H 2S is predicted to protect against pitting by shifting the free corrosion potential cathodically. The temperature is shown to have little effect on the pitting potential, at least, in the temperature range studied (up to 90°C).

Pitting is necessary, but not sufficient, for cracking to occur. It is predicted that the factors influencing pitting in these environments will also control the cracking. The applied load, in conjunction with pitting, is also found to be an important variable.

Committee:

Calvin Baloun (Advisor)

Subjects:

Engineering, Chemical

Keywords:

Pitting and Cracking Resistance; Potentiostatic Polarization Curves; NaOH solutions saturated with CO 2

Colwell, Alex MDevelopment of a stochastic metastable pit initiation model with transition to a stable pit state
Master of Science, University of Akron, 2016, Applied Mathematics
A stochastic pit initiation model, using the kinetic Monte Carlo method to simulate localized corrosion, is developed and examined numerically. The model contains both metastable pitting and transition to stable pits components. The metastable pit model uses a non-homogeneous Poisson process with specified generation rates. The metastable pit generation rate takes into account material parameters, such as the pitting potential, and several environmental factors influencing metastable pit formation: chloride levels, sulfur dioxide levels, and time of wetness. The formation of a metastable pit causes a brief spike in current on the surface of the metal. Stable pits are formed when overlapping current spikes from multiple metastable pits reach a required threshold current. Each threshold current is specific to the metal being observed and is derived from the Galvele criterion, that the product of the current density and the pit depth must exceed a critical value. The model determines the chronological formation of metastable pits and their transition from metastable to stable growth in order to track the accumulation and formation of metastable pit and stable pit densities. The model is benched marked against literature field data collected on AA1050 and laboratory data collected on AA7075.

Committee:

Nao Mimoto (Advisor); Curtis Clemons (Advisor); Kevin Kreider (Advisor)

Subjects:

Applied Mathematics

Keywords:

Corrosion, Pitting, Metastable pit initiation, Stable pit transistion

Roland, Zachary RGalvanically Induced/Accelerated Crevice Corrosion
Master of Science, University of Akron, 2016, Applied Mathematics
In this thesis, a one dimensional model is developed to investigate the initial stages of corrosion in a fastener assembly consisting of a stainless steel fastener and aluminum 7075 as the plate. Di fferential equations are formulated and solved to determine the pro files for the potential, the oxygen concentration, and the aluminum ion concentration in the crevice, and also the potential in the bulk electrolyte. This fastener system exhibits galvanic corrosion, pitting corrosion, and crevice corrosion. It is found that the potential decreases monotonically down the length of the crevice, the oxygen concentration decreases exponentially down the length of the crevice, and the aluminum ion concentration builds up away from the mouth of the crevice. It is conjectured that the location of maximum aluminum ion concentration is where the most severe corrosion will occur. A parameter study is also done to study the effect of changes to the di ffusivity, crevice width, and other parameters on the model calculations.

Committee:

Curtis Clemons, Dr. (Advisor)

Subjects:

Applied Mathematics

Keywords:

corrosion; galvanic; crevice; pitting; aluminum; steel; model

Chen, YajieMicrobiologically influenced corrosion of carbon steel caused by a sulfate reducing bacterium
Doctor of Philosophy, University of Akron, 2016, Chemical Engineering
Sulfate reducing bacteria (SRB) are common culprits of microbiologically influenced corrosion (MIC) that has been reported to cost $138 billion annually in the United States. Most literature reported the study results of SRB-induced corrosion when organic nutrients were provided to bacteria. But SRB-metabolizable organic substrates are not always available in the field conditions. There is a clear need to identify how SRB can induce pitting under the condition of long term starvation of organic substrates. The goals of this work are to elucidate the corrosion mechanisms of organic starving SRB on carbon steel (C1010) and propose possible MIC mitigation approaches. The specific objectives are: (1) monitoring MIC by correlating results of electrochemical impedance spectroscopy (EIS) and potential difference (PD) with measurements of bioactivities, biofilm and corrosion deposits; (2) development of a faster methodology for pit characterization to significantly reduce characterization time; (3) explication of the survival and corrosion mechanisms of a well-known SRB, D. vulgaris under long term starvation; and (4) development of possible MIC mitigation approaches. Coupons and sulfate-reducing biofilms were examined by confocal laser scanning microscopy (CLSM), infinite focus microscopy (IFM), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Bioactivities in the liquid phase were measured by high-performance liquid chromatography (HPLC) and various biological assays. Metal-biofilm interfacial layer evolution was monitored by EIS and PD. Our results supported the following conclusions: (1) EIS may be used for online monitoring of biofilm and corrosion product evolution, but the signals are complicated and require more systematic studies to improve understanding and ensure correct interpretation. Under certain conditions, pitting occurrence might be detectable from inner layer porous resistance and PD profiles. (2) Empirical correlations that enable fast estimation of maximum and average pit depths and pitted area percentage from the standard 3D surface parameters obtainable with IFM were established. (3) D. vulgaris, a common H2-utilizing SRB can survive on carbon steel up to 46 days under organic starvation by coupling direct electron uptake from steel surface with sulfate reduction. Direct cell attachment to metal is essential for this survival mechanism and the resultant pitting corrosion. (4) Future mitigation approach should target at preventing direct cell attachment or killing all the cells of biofilm including innermost layer of cells. KH2PO4 was demonstrated to be a promising MIC inhibitor by significant reduction of sessile SRB number and inhibition of pitting and intergranular corrosion.

Committee:

Lu-Kwang Ju (Advisor); Bi-min Zhang Newby (Committee Member); Gang Cheng (Committee Member); John Senko (Committee Member); Christopher Miller (Committee Member)

Subjects:

Chemical Engineering; Materials Science; Metallurgy; Microbiology

Keywords:

microbiologically influenced corrosion; sulfate reducing bacteria; infinite focus microscopy; pitting corrosion; intergranular corrosion; confocal microscopy; impedance spectroscopy; Desulfovibrio vulgaris; biofilm; biocorrosion; carbon steel; roughness

Tilson, Nial RobertAn Experimental Evaluation of Micro-pitting Performance of Two Bearing Steels
Master of Science, The Ohio State University, 2013, Mechanical Engineering
This experimental study focuses on the impact of operating conditions including entraining speed, sliding ratio, and load on micro-pitting performance of two typical bearing steels. Case hardened roller specimens made of alloy 9310 and through-hardened roller specimens made of alloy 485-2 are procured. Test matrices are defined according to the Latin Hypercube Space Filling Design of Experiment approach and executed to evaluate the micro-pitting performance of both materials by manipulating the speed, sliding ratio, load, and material. A two-disk test set-up is used for this purpose with each test documented by initial, interim, and final roughness, wear, and micro-pitting measurements. Before each test, a run-in process is implemented for the purpose of surface roughness break-in. By counting the distributed micro-pitted areas on the surface, a Micro-pitting Severity Index (MSI), defined as the ratio of the total micro-pitted area to the entire inspection area, is quantified for every test condition. Results indicate that the 9310 specimens showed significantly better resistance to micro-pitting compared to the 485-2 specimens, with nearly ten times lower MSI values. The data collected in this study establishes a database for micro-pitting failure of these two steel alloys that is required for validation of point contact lubrication models with circumferentially oriented surface roughnesses.

Committee:

Ahmet Kahraman, Dr. (Advisor); Robert Siston, Dr. (Committee Member)

Subjects:

Engineering; Materials Science; Mechanical Engineering

Keywords:

Micro-pitting; micro-pit; elastohydrodynamic lubrication; ground specimens; surface failure

McKinnon, John MotleyCorrosion Damage Evolution of a Unidirectional Pit
Master of Science, University of Akron, 2016, Applied Mathematics
A three-stage, unidirectional pit growth model, from initiation to stable growth and repassivation as the bulk potential is decreased, is developed. Stage I models metastable pit growth under ohmic control and a constant current density. Here it is assumed that the pit is covered by a semi-permeable oxide layer. Stage I is terminated when the metal concentration reaches its saturation limit at which time the pit cover instantaneously bursts. Stage II models the stable pit growth under diffusion control and the formation of a salt film at the bottom of the pit. During Stage II the bulk potential is decreased at a specified scan rate. When the bottom pit potential reaches the transition potential, Stage III begins. Here we model the pit growth under ohmic control, for a prescribed polarization curve, until the metal repassivates as the potential is decreased. The governing system of equations for each stage is solved numerically to determine the potential drop, and the concentrations of sodium, chloride, and metal ions within the pit. The pit depth as a function of time is determined from Faraday's Law in Stages I and III, and from a mass balance at the electrolyte/metal interface in Stage II. The cumulative pit depth is fit to a power law model that is used in existing Markov models for pit initiation and growth, and is compared with experimental pit depths for stainless steel in seawater.

Committee:

Curtis Clemons, Dr. (Advisor); Kevin Kreider, Dr. (Committee Member); Gerald Young, Dr. (Committee Member); Timothy Norfolk, Dr. (Committee Chair)

Subjects:

Mathematics

Keywords:

pitting corrosion; unidirectional pit growth; corrosion damage evolution; ohmic controlled; diffusion controlled; metastable growth; stable growth; repassivation; stainless steel in seawater

Unocic, Kinga AngelikaStructure-Composition-Property Relationships In 5xxx Series Aluminum Alloys
Doctor of Philosophy, The Ohio State University, 2008, Materials Science and Engineering
Al-Mg alloys are well suited for marine applications due to their low density, ease of fabrication, structural durability, and most notably resistance to corrosion. The purpose of this study is to investigate the effects of alloying additions, mechanical processing and heat treatments on the development of grain boundary phases that have an effect on intergranular corrosion resistance (IGC). Through modification of the standard AA5083 composition with extra additions of Cu and Zn and in conjunction with a long sensitization heat treatment (in excess of 1000 hrs at 165°C) it is possible to form a corrosion resistance modified τ-phase along grain boundaries. From an economical standpoint it is too costly to heat treat an alloy for such a long period of time and therefore an alternative method of producing a corrosion resistant alloy has been explored. Cu, Zn, and Si modified compositions were produced and were subjected to a high degree of cold work and shorter sensitization times. Following ASTM G67 intergranular corrosion testing and a detailed microstructural characterization, an optimal composition and processing condition that yielded the best intergranular corrosion resistance was determined. The microstructural development that led to these findings and issues with TEM sample preparation will be discussed in detail.

Committee:

Glenn Daehn, PhD (Advisor); Michael Mills, PhD (Committee Member); Buchheit Rudolph, PhD (Committee Member); Partridge Mark, PhD (Committee Member)

Subjects:

Materials Science

Keywords:

Al-Mg alloys; Al3Mg2; Intergranular corrosion; pitting corrosion

Chen, DongUltrasonic Control of Ceramic Membrane Fouling Caused by Silica Particles and Dissolved Organic Matter
Doctor of Philosophy, The Ohio State University, 2005, Civil Engineering
This study systematically investigated the mechanism and efficiency of the ultrasonic control of gamma-alumina ceramic membrane fouling caused by silica particles and dissolved organic matter (DOM). Ultrasound at 20 kHz was applied to a cross-flow filtration system. First, ultrasonic cleaning was explored with filtration of silica particles to investigate influence of both particle characteristics and ultrasonic factors on cleaning. Experimental results indicated that more effective control of fouling occurring at low particle concentrations, hydrophilic particles, and large particle sizes based on measurements of sound wave intensity, images of the cavitation region, and force balance analysis of a particle deposited on the membrane. In addition to the effect of particle characteristics, ultrasonic factors affecting membrane cleaning were explored. Optimal cleaning occurred when the membrane was outside but close to the cavitation region. However, damage in the form of pits and cracks were found when the membrane was within the cavitation region. An increase in the filtration pressure resulted in less improvement in permeate flux of ultrasound. Furthermore, pulsed ultrasound with short pulse intervals resulted in a relative permeate flux improvement close to that of continuous sonication. Second, besides sonophysical cleaning of particle fouled membranes, membrane cleaning was also explored by studying sonochemical reactions of DOM. Property changes of Aldrich and Pahokee peat DOM at different ultrasonic frequencies and energy densities were systematically investigated. Exposure of DOM to ultrasound resulted in decreases in hydrophobicity, aromaticity, and molecular weight, while DOM acidity increased. However, at low ultrasonic frequency (20 kHz) and low energy density, sonochemical transformation of DOM was insignificant. Finally, the effect of solution chemistry on ultrasonic control of membrane fouling caused by DOM and silica particles was examined. Experimental results indicated that more effective control of membrane fouling occurred at high pH, low ionic strength, and in the absence of divalent cations, due to stronger electrostatic repulsion among DOM macromolecules, silica particles, and the membrane. The decrease of the DOM rejection rate by ultrasound may be explained by the decreased steric exclusion effect, because ultrasound partially released membrane pore blocking and/or partially removed the foulant layer from the membrane surface.

Committee:

Linda Weavers (Advisor)

Subjects:

Engineering, Environmental

Keywords:

ultrasound; ultrafiltration; membrane cleaning; membrane fouling; luminol; cavitation; pitting; natural organic matter; dissolved organic matter;Aldrich; Pahokee; 13C NMR; aromaticity; oxidation

Nunez Moran, Emerson OsvaldoEvaluation of the Localized Corrosion Resistance of 21Cr Stainless Steels
Master of Science, The Ohio State University, 2010, Materials Science and Engineering
Ferritic stainless steels have good corrosion resistance properties and lower cost than austenitic steels due to the lack of nickel. However, they have a lower formability than that of austenitics, and they show brittleness at low temperatures, near 475°C, and of welds. Pohang Steel Company (POSCO) has interest in a 21% Cr ferritic stainless steel, which is a concentration that is relatively unexplored. Pitting corrosion of stainless steels is associated with surface defects and heterogeneities in the matrix, in particular inclusions, however, there is little information about the initiation sites in clean steels, with low S content. Therefore, it is of interest to investigate where the most susceptible sites for pitting initiation are located, and the role they play. The corrosion resistance of the ferritic alloys was evaluated and compared to the performance of austenitic SS304 steel using crevice corrosion tests and cyclic polarization tests in chloride solution to determine the pitting and repassivation potentials of the alloys. The role that inclusions play during pitting was evaluated for the ferritic stainless steels through a chemical attack experiment where the alloys were exposed to an acidic chloride solution and the progression of the attack was assessed at defined inclusions and discrete time intervals. The pitting potential (Epit) distribution of the ferritic alloys shows values ranging from 100 mV to 450 mV higher than those observed on SS304, indicating a higher resistance to pit initiation for the ferritic steels. In the crevice corrosion test, SS304 showed higher repassivation potentials (Erep) than the ferritic steels and in the pitting corrosion test the Erep values were higher for the ferritic steels. In both cases, however, the difference in Erep was about 100 mV. The differences in Erep between crevice and pitting may be caused by a strong dependence of Erep on the charge density in the low charge density region associated to pitting. The attack under a crevice former has larger dimensions than a pit, and thus the crevice repassivation potential might be different than that for pits. The higher repassivation potential for deep crevices found for SS304 indicates a better resistance to localized corrosion propagation. The combination of this result with the higher pitting potentials for the ferritic stainless steels suggests that the localized corrosion resistance of the ferritic steels is about the same as for SS304. The inclusions present in the ferritic stainless steels acted as pit initiation sites, due to their cathodic behavior compared to the metal matrix, promoting the dissolution of the metal matrix surrounding them.

Committee:

Gerald Frankel (Advisor); Rudolph Buchheit (Committee Member)

Subjects:

Automotive Materials; Engineering; Materials Science; Metallurgy

Keywords:

Corrosion; pitting; NMI; Stainless steel; ferritic; inclusion

Maier, BastianElectrochemical studies under thin electrolyte layers using a Kelvin Probe
Doctor of Philosophy, The Ohio State University, 2010, Materials Science and Engineering

In this study, electrochemical experiments were performed under thin electrolyte layers using a Kelvin Probe (KP). In the first part of this dissertation, cathodic polarization experiments of stainless steel 304L were conducted under a thin layer of chloride containing solution. Cathodic polarization curves exhibited a limiting current density associated with oxygen reduction. The limiting current density varied with solution layer thickness over a finite range of thickness. Furthermore, pitting of stainless steel 304 under droplets of MgCl2 solution was monitored. Droplets of different volumes of MgCl2 solution were placed on the steel surface and exposed to a constant low relative humidity (RH). As the concentration increased during exposure of the drop to low RH, the open-circuit potential (OCP) and the shape change of the drop were monitored by the KP. Pit initiation was detected by a sudden decrease in the OCP. Pits initiated earlier under small droplets than under large drops. The chloride concentration at initiation was found to be between 3.0 and 8.4 M for droplets with a starting concentration of 0.88 M Cl-. The anodic current demand of pits growing at OCP decreased with time as did the available cathodic current. When the current demand exceeded the available cathodic current, the active pit area decreased. The pit current density for OCP pits was found to be much lower than for potentiostatically-controlled pits in dilute solutions. Additionally, pitting corrosion behavior of stainless steel 304 under an electrolyte droplet with a layer of silica particles on the surface was investigated by using a KP. Droplets of 2.5 M MgCl2 solution were placed on silica-coated steel surface and exposed to a constant low relative humidity. Due to evaporation of water, the chloride concentration increased. At a certain value pitting initiated, which was detected by a sudden drop in open circuit potential. Metastable pits repassivated slower under the silica particle layer than on bare stainless steel. Pits on silica-coated SS304 initiated within a narrow chloride concentration and time range unlike pits on bare SS304. Pit growth rate was not influenced by the silica layer.

In the second part of this dissertation, the electrochemical behavior of magnesium-rich primer (MgRP) on AA2024-T3 was investigated with a KP. MgRP was developed based on the mechanism of Zn-rich primer for steel. It was suggested that the Mg pigment in the organic matrix acts as sacrificial anode and the aluminum substrate is cathodically protected. To get a deeper understanding of this mechanism different Mg rich coating systems were compared with each other and galvanic corrosion experiments were performed between bare AA2024-T3 and AA2024 T3 coated with MgRP. The electrochemical properties of Mg-rich coatings primarily depend on the polymer matrix whereas the source of Mg pigment plays a secondary role. Basic or cathodic corrosion of AA2024-T3 is possible for samples coated with Mg-rich primer. Thin electrolyte layer experiments in different gases showed that the amount of CO2 available in the air was not enough to buffer OH- from Mg corrosion products and oxygen reduction. Cathodic or basic corrosion took place.

Committee:

Gerald S. Frankel (Advisor)

Subjects:

Materials Science

Keywords:

Kelvin Probe; pitting; stainless steel; magnesium rich primer; cathodic corrosion

Cao, LiuCorrosion and Stress Corrosion Cracking of Carbon Steel in Simulated Fuel Grade Ethanol
Doctor of Philosophy, The Ohio State University, 2012, Materials Science and Engineering

Carbon steel is susceptible to stress corrosion cracking (SCC) in fuel grade ethanol. Dissolved oxygen and corrosion potential have been identified as the critical factors. The threat of SCC prevents the use of the cost-efficient pipeline system for long distance transport of ethanol. Simulated fuel grade ethanol (SFGE) was used in the laboratory. Due to the high electrical resistivity of SFGE, adding non-complexing supporting electrolyte is considered to be the most practical method for accurate potential control. TBA-TFB was found to be the best suitable supporting electrolyte in deaerated FGE among the salts that were tested.

Carbon steel exhibits passivity and high corrosion potential in aerated SFGE. Deaerated conditions are of interest so that the effects of high potential on SCC susceptibility can be determined separately from other possible effects of dissolved oxygen. In slow strain rate (SSR) tests, cracking was reproduced at applied potential without oxygen in the deaerated SFGE + TBA-TFB, which indicates that the role of oxygen in ethanol SCC might be a simple oxidizing agent. However, the passivation effect of oxygen is also required to prevent lateral corrosion at crack tip. A potential range for ethanol SCC was determined by SSR tests at different potentials. No experimental evidence was found to support the proposed role of oxygen to react with ethanol to form an aggressive oxidation product.

The presence of chloride causes decreasing corrosion potential and enhanced pitting corrosion. The chloride effect on ethanol SCC was investigated both in aerated SFGE at open circuit and deaerated SFGE at applied anodic potentials over a wide range of chloride concentration. A minimum concentration of chloride is required for SCC of carbon steel, but it is not the controlling factor for crack growth. There is no upper limit of chloride concentration for cracking in aerated SFGE, but a window of chloride concentration in deaerated SFGE at applied potential.

The dissolution based SCC mechanism has been identified for carbon steel in ethanol environment. SSR testing with periodic potentiodynamic scans at different stains and strain rates show that the anodic current difference between plastic and elastic region has a peak in the cracking potential range. The notched SSR testing is more sensitive to ethanol SCC susceptibility, and it generates more consistent results of current evolution. A high R-ratio and low cyclic frequency crack growth rate (CGR) test was intended to mimic the actual loading condition of pipelines in service at accurately-controlled fracture mechanics conditions. The measured CGR at applied potentials matches the cracking susceptible potential region.

An oxygen depletion induced dissolution model and the traditional film rupture induced dissolution model were proposed to explain the mechanism of ethanol SCC. A few models based on oxygen diffusion and consumption were considered in an attempt to explain the differences of the two proposed mechanisms. Complete oxygen depletion is less likely to occur at crack tip.

Committee:

Gerald Frankel, Dr. (Advisor); Narasi Sridhar, Dr. (Committee Co-Chair); Rudolph Buchheit, Dr. (Committee Member); Glenn Daehn, Dr. (Committee Member)

Subjects:

Engineering; Materials Science; Metallurgy

Keywords:

biofuel; fuel grade ethanol; pitting corrosion; stress corrosion cracking; carbon steel; IR drop; supporting electrolyte; crack growth rate; dissolved oxygen; corrosion potential; chloride

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