NORTHWESTERN UNIVERSITY Tribology And Corrosion In
NORTHWESTERN UNIVERSITYTribology and Corrosion in CoCrMo Alloys and Similar SystemsA DISSERTATIONSUBMITTED TO THE GRADUATE SCHOOLIN PARTIAL FULFILLMENT OF THE REQUIREMENTSfor the degreeDOCTOR OF PHILOSOPHYField of Materials Science and EngineeringByEmily E. HoffmanEvanston, ILMarch 2017
2 Copyright by Emily E. Hoffman, 2017All Rights Reserved
3Tribology and Corrosion in CoCrMo Alloys and Similar SystemsEmily E. HoffmanThe artificial hip is a rich environment for the tribologist. This research investigatedtribology and corrosion in CoCrMo alloy hip implants and extended the characterization methodsand analyses to similar systems. The first project examined differences in corrosion behavior inthe biomedical CoCrMo alloy using TEM and EDS. At the corroding grain boundaries, we foundnanoscale chromium-rich carbides. These carbides caused chromium depleted zones which leadsto corrosion, a process commonly referred to as sensitization. The chromium depletion and grainboundary crystallography data were used to develop a model showing nanoscale sensitizationinitiated grain boundary crevice corrosion. The next area of research looked at nanotribology ofsolid lubricants and formation of tribolayers. In situ TEM was used to directly observe the slidinginterface of nanoflakes of molybdenum disulfide. Investigating low friction mechanisms of thelamellar solid lubricant revealed that the deck-of-cards sliding assumption present in the literaturewas not true. Instead, we showed sliding and transfer layer formation occurred at one interfaceonly. The in situ sliding tests also revealed that the nanoflakes are unstable during sliding due torolling, reorientation, flake pull apart, and adhesion changes. The final project analyzed a varietyof carbon tribofilms, including the tribolayer found in metal-on-metal hips and the varnishtribofilm that forms in industrial machines. We characterized the carbon varnish film and showedsimilarities to published work on other graphitic carbon films. By comparing the nanoscalebonding and formation mechanisms, striking similarities were found that could inspire futurecross-discipline advancements. Together, this work examined the relationships between wear,corrosion, and tribology to connect nanoscale structure and composition to applied performance.
4AcknowledgmentsFirst I would like to acknowledge my advisor Laurie. Thank you for being patient andencouraging. Thank you for allowing me to make my graduate experience my own with theprograms and the internship that I wanted to pursue. Additionally, I would like to thank mycommittee, Dr. Ken Shull, Dr. Peter Voorhees, Dr. Markus Wimmer, and Dr. Ali Erdemir.There are many people who helped me scientifically. Ben Myers, thank you for managing theFIB and for always being willing to help troubleshoot. To the TEM managers, Jinsong Wu at EPIC,Alan Nicholls at UIC, and Jie Wang and Nestor Zaluzec at Argonne, thank you for your trainingand help. Thank you for giving me the skills I needed to complete this thesis.Thank you to the excellent Marks Group, both past and current. It has been a pleasuring sharingthe journey of graduate school with you. Yifeng, I am glad that I had you as a mentor when Ientered the Marks Group. Your calm, patience, sense of humor, and intelligence were traits tolearn from. Pooja, thank you for starting your interesting work on the CoCrMo samples. It wasgreat to learn from you and carry on the work. Thank you Alex, we have accomplished so muchtogether. Thanks to Tiffany for putting together a great webpage for my tribology videos.I’ve met many wonderful and interesting people during graduate school who have encouragedme. Thank you to the wonderful mat scis. It’s been a pleasure to be in this department with suchfun, smart, and caring people. I have been proud to be part of MSSA and every mat sci IM sportsteam. Ricardo, Bernie, Elizabeth, Dana, and Sauza, thank you for the food adventures, cook outs,yoga, and plain old goofing off. To my wonderful roommate David, I could not have asked for abetter roommate in my last year of grad school. To Stephanie, thank you for diving into the worldof SWE with me, it’s been fun. Thank you to Erin, for listening to me when I needed to talk themost. Thanks to Ellen, who got me to volunteer at the Moth in Chicago, befriended me, and
5introduced me to her welcoming group of friends. Asa, Emily, Sam, Margaret, and Emily, thankyou for all the camping, picnics, and perspective.To my family, thank you for always believing that I would be successful. Thank you to mymom and dad for listening to me as I worried and providing a relaxing and loving home to escapeto for the holidays. Thank you to my siblings Amanda, Ethan, Maddie, and Becca. And alwaysthank you to my best friend, Laurel, who is basically family too.To my partner Sam, thank you. I am so glad I found you. Thank you for encouraging me tobike around the city and drink Belgian beer. Thank you for asking me about my research and mycareer aspirations. Thank you for reading over my cover letters and doing case practices with me.Thank you for proofing my work, including this thesis. I look forward the fun to be had with you.I also want to formally acknowledging my funding sources. The majority of this work wasfunded by the National Science Foundation, Grant Number CMMI-1030703. The experiments inChapters 4 and 5 were performed at the Electron Microscopy Center of the Center for NanoscaleMaterials at Argonne National Laboratory, a U.S. Department of Energy, Office of Science, Officeof Basic Energy Sciences User Facility under Contract No. DE-AC02-06CH11357. I would alsolike to thank ATI Allvac for the original donation of the CoCrMo alloy materials used in Chapters2 and 3, and C.C. Jensen and Dyna Power Parts of the varnish materials used in Chapter 6.I have been personally funded through the Department of Defense National Defense Scienceand Engineering Graduate Fellowship (NDSEG). In 2012, I was funded by the BiotechnologyTraining Center Cluster Program, a National Science Foundation training program. In 2013, Ireceived a fellowship from my sorority through the Delta Gamma Foundation GraduateFellowship. I am thankful to have been well-supported throughout my graduate career.
6List of AbbreviationsADFannular dark fieldAFMatomic force microscopyAPTatom probe tomographyBCSbovine calf serumBFbright fieldCDZchromium depleted zoneCoCrMocobalt chromium molybdenumCSLcoincidence site latticeCVDchemical vapor depositionDLCdiamond like carbonDFdark fieldDOSdegree of sensitizationEBSDelectron back scatter diffractionEDSenergy dispersive X-ray spectroscopyEELSelectron energy loss spectroscopyEISelectrochemical impedance spectroscopyEPRelectrochemical potentiokinetic reactivationETEMenvironmental transmission electron microscopyFIBfocused ion beamFTIRFourier transform infrared spectroscopyGACCgrain boundary assisted crevice corrosion
7HAADFhigh angle annular dark fieldHChigh carbonHOPGhighly ordered pyrolytic graphiteIF-MoS2fullerene like molybdenum disulfideIGCintergranular corrosionIGSCCintergranular stress corrosion crackingLEAPlaser emission atom probeMEMSmicroelectromechanical 2molybdenum disulfideNEMSnanoelectromechanical systemOIMorientational image mappingPBSphosphate buffered salinePVDpulse vapor depositionSIFTsoft interface fracture transferSIMSsecondary ion mass spectroscopySTEMscanning transmission electron microscopyTEMtransmission electron microscopyTHAtotal hip arthroplastyUHMWPEultra-high molecular weight polyethyleneVTRvideo tape recorderXPSX-ray photoelectron spectroscopy
8Contents12Background . 251.1Tribology . 251.2Hip Implants . 271.3Solid Lubricants . 301.4Microscopy: TEM and In-situ TEM . 331.5Outline of Research . 36Grain Boundary Assisted Crevice Corrosion in CoCrMo Alloys . 382.1Introduction . 392.2Grain Boundary Sensitization . 422.3Methods . 482.42.3.1CoCrMo Alloy . 482.3.2Electrochemical Corrosion Testing . 492.3.3Electron Backscatter Diffraction . 502.3.4White Light Interferometry . 512.3.5Focused Ion Beam . 522.3.6Transmission Electron Microscopy and Energy Dispersive X-ray Spectroscopy. 532.3.7Atom Probe Tomography . 54Results . 54
92.53Grain Boundary Assisted Crevice Corrosion (GACC) Model . 652.5.1Local Grain Boundary Attack. 662.5.2Including the Role of Crevice Corrosion . 702.6Discussion . 722.7Conclusions . 76Effect of Coincident Site Lattice and Chromium Segregation on Grain Boundary AssistedCrevice Corrosion in CoCrMo Alloys . 773.1Introduction . 783.2Methods . 813.33.2.1Sample Preparation . 813.2.2Scanning Electron Microscopy . 823.2.3White Light Interferometry . 833.2.4Focused Ion Beam . 843.2.5Transmission Electron Microscopy . 84Results . 853.3.1Grain Boundary Misorientation . 853.3.2Effect of Misorientation on Carbide Precipitates . 903.3.3HAADF and EDS Quantification of Chromium Depletion. 933.4Corrosion (GACC) Model Expansion to Type II Grain Boundaries . 993.5Discussion . 1033.6Conclusions . 105
10456Soft Interface Fracture Transfer in Nanoscale MoS2 . 1064.1Introduction . 1074.2Experimental Methods . 1124.3Results . 1144.4Discussion . 1204.5Conclusions . 1254.6Video Captions . 126Molybdenum Disulfide Sliding Modes . 1275.1Introduction . 1275.2Materials and Methods . 1325.3Results . 1345.4Discussion . 1445.5Conclusions . 1475.6Video Captions . 148Graphitic Carbon Films Across Systems . 1496.1Introduction . 1506.2Systems . 1546.2.1Friction Polymers . 1556.2.2DLC Coatings . 160
116.36.46.576.2.3Varnish in industrial machines . 1616.2.4MoM Hips. 1676.2.5MEMS . 1696.2.6Non-tribology: Catalysis Coke . 1716.2.7Other Examples: Cast Iron, Video Tape, Nanocomposite Coating . 173Mechanisms of Formation. 1766.3.1Pressure, Temperature, and Friction . 1766.3.2Depositions and Adsorption . 1786.3.3Polymerization and Organometallics. 1806.3.4Catalytic Activity and Fresh Surfaces . 1826.3.5Graphitization . 1846.3.6Nanoparticles and Metal Particles . 185Discussion . 1866.4.1Similarities . 1866.4.2Thermodynamics . 1886.4.3Future Opportunities . 191Conclusions . 192Future Work . 1947.17.2CoCrMo Alloy . 1947.1.1Experiments with the Current CoCrMo Alloy Samples . 1947.1.2Future Directions of CoCrMo Alloy Research . 195Varnish . 198
127.3In situ . 2007.3.1Improving our Experimental Setup . 2007.3.2Further Analysis of Current Experiments . 2047.3.3Similar Materials . 2077.3.4New Collaborations for In Situ Sliding . 2078References. 2109Curriculum Vitae . 240
13List of TablesTable 2.1 Composition of the high-carbon CoCrMo alloy. . 48Table 2.2 EDS quantification, Figure 2.14 carbide. . 62Table 2.3 EDS quantification, Figure 2.15. . 63Table 2.4 Summary of Averaged EDS quantifications. . 63Table 2.5 EDS quantification, Figure 2.16 carbide. . 64Table 3.1 High-carbon CoCrMo alloy composition. . 81Table 3.2 EDS quantification of key regions in Figure 3.10. . 95Table 3.3 EDS quantification of key regions in Figure 3.11. . 95Table 3.4 EDS quantification of key regions in Figure 3.12. . 96Table 3.5 EDS quantification of key regions in Figure 3.13. . 96
14List of FiguresFigure 1.1 An ancient tribologist in the tomb of Tehuti-Hetep, circa 1880 B.C. The man atthe foot of the statue is pouring a lubricant (from Ref [1]). . 26Figure 1.2 Asperities on asperities as the magnitude of magnification increases. . 27Figure 1.3 (a) Complete total hip replacement system with modular parts and (b) X-rayshowing implanted metal-on-metal hip replacement [10]. . 29Figure 1.4 The layered structure of MoS2 allows for low friction sliding between monolayersheets. . 31Figure 1.5 Schematic of the holder. A tip is brought into contact with the sample duringobservation in the microscope. Both the normal force (AFM holder) and I-Vcharacteristics can be measured during the experiments, in addition to normal TEMimaging and spectroscopies. . 35Figure 2.1 Carbide presence at a grain boundary may take the form of (a) a complete networkalong the grain boundary, (b) micron scale precipitates along some parts of theboundary, or (c) nanoscale precipitates unable to be seen at the micron scale. . 44Figure 2.2 From Panigrahi et al. [65]. Relative frequencies of grain boundary geometries forcorroded and immune boundaries. The fcc grain boundary geometries are listed inorder of decreasing lattice coincidence. . 46Figure 2.3 From Panigrahi et al. [65]. (a) As received wrought structure with 3-5 μm grains.(b) After 24 hour anneal at 1230 C the grains grew to 100-300 μm with few secondphases. (c) Corroded surface of as received wrought. (d) Corroded surface after 24hour anneal at 1230 C. Note the differing scale bars. . 49
15Figure 2.4 (a) SEM image showing a single grain boundary being cut from the bulk sample,(b) the lamellar viewed in SEM comprising of the two grains with the grainboundary, indicated by the dotted line down the middle, (c) a sample viewed inTEM again with the dotted line on the grain boundary, and (d) layout of a typicalcorroded sample. 52Figure 2.5 The EBSD generated (a) SEM images, (b) OIM images, and (c) labeled CSLboundaries of the scanned region, later identified in the FIB/SEM for TEM samplepreparation. . 55Figure 2.6 Depth and width measurements collected from 3D profilometry showed that thecorrosion width was approximately 2-5 times larger than its corresponding depth.With square as CSL and diamond as non-CSL, each point represents a singleboundary, where the arrows represent the range of the multiple measurements alongthat boundary. . 55Figure 2.7 The initial examination in bright field TEM showed (a) the corroded boundarieshave a wavy structure, where each bend was a carbide feature at the boundary,whereas (b) immune boundaries were straight and featureless. . 57Figure 2.8 (a) Bright field TEM image with an EDS map, Co green, Cr red, and Mo blue from a JEOL 2100. The dotted line indicates the grain boundary, with achromium enhancement. Line scans (b) and (c) indicate the change in concentrationat the carbide. 57Figure 2.9 (a) Bright field image of a grain boundary with a chromium-rich carbide. (b)Diffraction pattern of grain 1, (c) diffraction pattern of the feature showing a M23C6carbide grain structure, and (d) diffraction pattern of grain 2. . 58Figure 2.10 The chart summarizes the samples measured in each category and if carbideswere present. The boundary can be either CSL or non-CSL, and either be corroded
16or immune. The proportion of samples in each category represents the approximatefrequency seen in the bulk sample. 58Figure 2.11 (a) The lens shape of the chromium-rich carbide with (b) the HREM showingthe shared epitaxial alignment with the concave grain. . 59Figure 2.12 Dark field selecting for (a) grain 1 and (b) grain 2, show the epitaxial nature ofthe chromium-rich carbide to the grain on the concave side of the lens. . 59Figure 2.13 The distinct shape of the chromium-rich carbides has been previously modeledby a copper indium alloy, with α as the trailing grain, α’ as the forward grain, andβ as the carbide [129]. . 60Figure 2.14 The chromium depleted region around a chromium-rich carbide, with (a) theADF image, (b) an extracted line scan to show the CDZ, (c) cobalt, (d) chromium,and (e) molybdenum. The arrow indicates where the line scan was taken, and thecircles indicate where the EDS spectra were quantized, reported in Table 2.2. . 62Figure 2.15 The chromium depleted region between two chromium-rich carbides, with (a)the ADF image, (b) cobalt, (c) chromium, and (d) molybdenum. The chromiumdepletion is measured along a 150 nm section of grain boundary between twocarbides and found to be sensitized by 2%. The circles indicate where the EDSspectra were quantized in Table 2.3. . 63Figure 2.16 Carbides less than 50 nm did not show measurable chromium depletion, with(a) the ADF image, (b) cobalt, (c) chromium, and (d) molybdenum. The circlesindicate where the EDS spectra were quantized in Table 2.5. . 64Figure 2.17 (a) A 10 nm thick slice of LEAP acquisition that intersected with a grainboundary and a carbide. (b) Composition profile through the edge of the carbideshowing the chromium segregation. (c) The gallium present from FIB thinningsegregated to the boundaries in the sample (black), which leaves a track of wherethe grain boundary is located. (d) The chromium concentration evaporating mainly
17at the grain boundaries of the carbide with a patch of uneven evaporation on theedge. 65Figure 2.18 The macro view of sensitization has large regions of chromium depletion,leading to incomplete oxide formation around the sensitized boundary. In nanoscalesensitization, the oxide is not significantly diminished. The chromium depletion ison a nanometer scale along the boundary. 67Figure 2.19 The model for grain boundary assisted crevice corrosion includes the CDZwidth (L), the distance between atoms along the grain boundary (a), the distancebetween atoms perpendicular to the grain boundary (b), and the depth of onemonolayer of atoms removed from the surface (d). The weighted average diameterof Co and Cr can be used for a, b, and d, while L is measured from the EDS maps. . 67Figure 2.20 The chromium oxide layer with the light gray representing the bulk, the darkgray representing the oxide, the black arrows representing the Cr3 movement andthe blue lines representing the CrOH2 concentration. As the chromium dissolutionproducts accumulate in the crevice, the reaction down is quenched and the corrosionoccurs out towards the walls of the crevice. The ions and albumin proteins are notto scale, but to serve as a representation. In the human body, many more ions andproteins would be present. . 71Figure 3.1 (a) A SEM image and (b) its corresponding EBSD map showing preferentiallycorroded CoCrMo grain boundaries and the different grain orientations. (c) CSLboundaries are labelled with red lines, twin boundaries are labelled with black lines,and randomly oriented grain boundaries are labelled with grey lines. . 86Figure 3.2 Representative examples of a (a) Type I, (b) Type II, and (c) Type III grainboundary as indicated by the arrows. . 87Figure 3.3 Profilometry measurements of the same region of interest can be shown as (a) a2D projection and (b) a 3D reconstruction. Depth profiles of representative (c) Type
18I, (d) Type II, and (e) Type III boundaries are shown. Type III boundary profiles,taken from 3 different sites along the boundary, show a large variance in the depthmeasurements. . 87Figure 3.4 Corrosion crevice depth was plotted with respect to the CSL Σ number. The threeclasses of boundaries and their respective corrosion depths are shown. . 89Figure 3.5 Crevice measurements collected from 3D profilometry show that widths of thecorroded grain boundaries are approximately 2-5 times larger than itscorresponding depth. The arrows represent the range of measurements along theboundary . 89Figure 3.6 BF TEM showed that a partially corroded Σ27 boundary was faceted by carbides. 91Figure 3.7 (a) The immune Σ17 grain boundary was straight without deviations and did notshow carbides. (b-c) Electron diffraction patterns collected at the adjacent grainsconfirmed the presence of a grain boundary. . 91Figure 3.8 BF TEM image of lens shaped carbides (indicated by arrows) at a partiallycorroded Σ25 grain boundary. . 92Figure 3.9 (a) Two carbides of approximately 100 nm are found along the Σ13 boun
Tribology and Corrosion in CoCrMo Alloys and Similar Systems Emily E. Hoffman The artificial hip is a rich environment for the tribologist. This research investigated tribology and corrosion in CoCrMo alloy hip implants and extended the characterization methods and analyses to
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