ENHANCEMENT OF NITI ALLOYS BIOCOMPATIBILITY AND CORROSION RESISTANCE BY ...

106 Pages·2016·9.6 MB·English

by  Andre C. Marta

ENHANCEMENT OF NITI ALLOYS BIOCOMPATIBILITY AND
CORROSION RESISTANCE BY THERMAL TREATMENTS
Gonçalo Nuno Vieira da Silva Mealha
Thesis to obtain the Master of Science Degree in
Chemical Engineering
Supervisor(s): Prof. Doctor João Carlos Salvador Santos Fernandes
Prof. Doctor Maria Teresa Oliveira de Moura e Silva
Examination Committee
Chairperson: Prof. Doctor Benilde de Jesus Vieira Saramago
Supervisor: Prof. Doctor João Carlos Salvador Santos Fernandes
Member of the Committee: Prof. Doctor Maria João Pedroso Carmezim
December 2016
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Acknowledgments
IwouldliketoaddressspecialthankstoprofessorJoa˜oSalvadorFernandes,supervisorofthisscientific
work,forgivingmetheopportunitytodevelopthisproject,forhispatience,guidance,supportandgiven
knowledgethroughthealltime.
I would like to thank Dr. Teresa Moura e Silva for her co-supervision, concern, advice, support and
encouragement.
ToDr. MariaJoa˜oCarmezim,Iwouldliketothankfortheperformedthermaltreatmentsonthesamples,
andforherconcernandsympathy.
I also would like to express my gratitude to all the professors and colleagues of Centro de Quimica
Estrutural(CQE)forhavingreceivedmesokindlyandfortheiravailabilitytohelpmewheneverIneeded.
ImustexpressaspecialthanktoMiguel,duetohisconstantsupport,availabilityandfriendship.
Finally, I am very grateful to all my friends, Maria and family, for their support and affection through the
entire time. I would like to thank to Patanisca, SL Benfica and GD Vialonga, for the joys they gave me
andforbeinganescapefromthiswork.
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Resumo
ONitinole´ umaligacompostaporn´ıqueletitaˆnio,emproporc¸o˜esato´micaspraticamenteiguais,eque
apresenta como propriedades mecaˆnicas efeito de memo´ria de forma e uma alta deformac¸a˜o ela´stica
(superelasticidade). Para ale´m destas propriedades, caracteriza-se por ter uma elevada resisteˆncia a`
fadiga e resisteˆncia a` corrosa˜o e por ser um material biocompat´ıvel, o que leva a` sua utilizac¸a˜o em
aplicac¸o˜esbiome´dicas.
Pore´m, a elevada presenc¸a de n´ıquel e a sua poss´ıvel libertac¸a˜o dos dispositivos de Nitinol e´ um
problema habitual destas ligas, o que pode levar a processos inflamato´rios e ale´rgicos por parte do
paciente.
Nestetrabalhoprocedeu-sea` modificac¸a˜odasuperf´ıciedoNitinolatrave´sdetratamentoste´rmicosem
dois tipos de atmosfera (ar e azoto) e duas diferentes temperaturas (250 °C e 350 °C). A resisteˆncia a`
corrosa˜o das amostras modificadas foi investigada atrave´s de te´cnicas electroqu´ımicas numa soluc¸a˜o
quesimulaomeiofisiolo´gico(soluc¸a˜odeHank)a37°CecomparadacomNitinolsemtratamento. Para
acaracterizac¸a˜odassuperf´ıciesresultantesforamusadasespectroscopiadefotoelectro˜esderaio-Xe
espectroscopiadeelectro˜esAuger.
Verificou-sequeostratamentosefectuadosteˆminfueˆncianocomportamentoelectroqu´ımicodoNitinol.
Atrave´sdeensaiosdeEIS,eporajusteaumcircuitoequivalente,considerou-seumaestrutura”duplex”
para o filme de o´xido, constitu´ıdo por uma densa camada interna e uma camada externa porosa. As
te´cnicasdeana´lisesdesuperf´ıciepermitemconcluirqueoteorden´ıquele´ substancialmentereduzido
nosfilmessuperficiaisapo´stratamentoa350°C,especialmenteematmosferadeazoto.
Palavras-chave:
Nitinol,biomateriais,corrosa˜o,tratamentoste´rmicos,filmedeo´xido
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Abstract
Nitinolisanickel-titaniumalloy,nearlyinthesameatomicproportion,whichcombinesuniquemechan-
ical properties, like shape-memory effect and high elastic deformation (superelasticity). In addition to
theseproperties,thematerialpresentshighfatiguestrength,corrosionresistanceandsuperiorbiocom-
patibility,whichturnsitsuitableforbiomedicalapplications.
Due to the high nickel presence, inflammatory and allergic processes may be initiated as result of the
releaseofnickelionsfromNitinoldevices,beingagreatproblemtoitsuse.
In the present work, thermal treatments were performed in the surface of Nitinol in two types of envi-
ronment(airandnitrogen)andattwodifferenttemperatures(250°Cand350°C).Corrosionresistance
of the treated alloys was analyzed through electrochemical techniques in simulated physiological con-
ditions (Hank’s solution at 37 °C) and the results were compared with untreated Nitinol. The modified
surfaceswerecharacterizedbyX-rayphotoelectronspectroscopyandAugerelectronspectroscopy.
The performed surface treatments proved to influence the electrochemical behaviour of Nitinol. From
EIS spectra, and by fitting the data to an equivalent circuit, a ”duplex” structure was proposed to the
alloy’s oxide film, composed by an inner compact layer and an outer porous layer. Results from the
surfaceanalysisconcludedthatthenickelcontentwassubstantiallydecreasedintheoutermostsurface
layers,especiallywhentreatedat350°CinN -controlledenvironment.
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Keywords:
Nitinol,biomaterials,corrosion,thermaltreatments,oxidefilm
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Contents
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Resumo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
ListofTables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
ListofFigures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
1 Introduction 1
1.1 TopicOverview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 ThesisOutline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Background 3
2.1 TheoreticalOverview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Nitinolcharacteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2.1 ShapeMemoryEffect(SME) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2.2 Superelasticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.3 Otherproperties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Biocompatibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.1 NiTiconstituents’materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3.2 BiocompatibilityofNiTi-invitro experiments . . . . . . . . . . . . . . . . . . . . . 11
2.3.3 BiocompatibilityofNiTi-invivo experimentsinanimals . . . . . . . . . . . . . . . 12
2.3.4 BiocompatibilityofNiTi-invivo experimentsofimplantsinhumans. . . . . . . . . 16
2.4 Corrosionresistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4.1 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4.2 CorrosionResistanceofNiTi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5 Coatingsandsurfacetreatments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.6 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.6.1 Self-expandablestents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.6.2 Orthodontics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.6.3 Orthopedics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
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2.6.4 Otherapplications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.7 Tribologyandotherconsiderations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3 ExperimentalMethods 47
3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.2 Materialsandsolutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3 Samplepreparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.3.1 Untreatedsamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.3.2 Thermallytreatedsamples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.4 ElectrochemicalMeasurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
3.4.1 Open-CircuitPotential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4.2 AnodicPolarizationCurves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4.3 ElectrochemicalImpedanceSpectroscopy(EIS) . . . . . . . . . . . . . . . . . . . 52
3.5 SurfaceAnalysisTechniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5.1 X-rayPhotoelectronSpectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.5.2 AugerElectronSpectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4 Results 61
4.1 Electrochemicalmeasurementsresults. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.1.1 OCPandAnodicpolarizationcurves . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.1.2 ElectrochemicalImpedanceSpectroscopy . . . . . . . . . . . . . . . . . . . . . . . 64
4.2 Surfaceanalysisresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5 ConclusionsandFutureWork 75
Bibliography 77
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