Implant Materials Titanium 6_ Aluminum 7_ Niobium

8/12/2019 Implant Materials Titanium 6_ Aluminum 7_ Niobium

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John Disegi

Second Edition

November 2008

About the Cover

A portion of the Periodic Table depicts various major implantalloying elements.

Alpha and beta crystal structure of Ti-6Al-7Nb.

AcknowledgementThe author wishes to acknowledge the technical contributions ofProfessor S. Steinemann, University of Lausanne, Switzerland.


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Introduction

Basic Metallurgy

Properties

References

Glossary

Table of Contents

2

1. Composition 3

2. Microstructure 4

1. Physical 5

2. Tensile 6

3. Fatigue 7

4. Corrosion 8

5. Biocompatibility 11

6. Surface 12

13

16


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Titanium 6% Aluminum 7% Niobium is a relatively new titaniumalloy that has been selected by Synthes for the next generation of ad-

vanced fracture fixation devices. The alloy was conceived in 1977 by ateam of researchers at Sulzer Bros., Winterthur, Switzerland.1

The new alloy was introduced by 1985 following six years of intensivedevelopment and testing. A total hip replacement (THR) prosthesisfabricated from Ti-6Al-7Nb was originally marketed by Protek asProtasul 100 and has been in clinical use since early 1986.

The mechanical properties of Ti-6Al-7Nb alloy are very similar toTi-6Al-4V alloy which has been used as a biomaterial for many years.

The major difference between the alloys is the replacement of vana-dium by niobium. The Ti-6Al-7Nb composition is in agreement with theprinciple of utilizing only non-toxic elements for implant devicesas outlined in U.S. Patent 4,040,129 assigned to Institute Straumann,Waldenburg, Switzerland.2

Niobium was discovered 3 while chemist C. Hatchett was analyzinga black stone near Connecticut in 1801. The element was originallynamed columbium and was assigned atomic number 41 in the Periodic

Table. Columbium was later renamed niobium which was derived fromNiobe, the goddess of tears in Greek mythology. The word niobiumwas preferred in Europe while the word columbium continued to beused in the United States.

Various niobium compounds are extracted from ore concentrates by achlorination process followed by metallic reduction to niobium metal.3

The metal is then purified by electron beam melting into ingots. Theingots are alloyed with specific metals and further refined in a vacuumconsumable arc melting furnace to produce an intermediate raw

material known as a niobium master alloy.

The niobium master alloy is blended with pure titanium in the correctproportion and a cylindrical electrode is formed for melting under highvacuum. Ti-6Al-7Nb alloy is double or triple vacuum arc melted toprovide an ingot composition that is very uniform and homogeneous.The ingot is hot pressed, hot rolled, and finished into round and flatbar products using conventional titanium alloy processing methods.

Introduction


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1. Composition

Composition requirements for Ti-6Al-7Nb alloy are included in ISO

5832-11 4 and ASTM F 1295 specification5. The composition limits forTi-6Al-7Nb alloy are listed as follows:

Basic Metallurgy

Ti6Al7Nb composition limits

Element Composition (%)

Aluminum 5.50 to 6.50

Niobium 6.50 to 7.50

Tantalum 0.50 max

Iron 0.25 max

Oxygen 0.20 max

Carbon 0.08 max

Nitrogen 0.05 max

Hydrogen 0.009 max

Titanium Balance

The product tolerance limits for chemical check analysis must meet therequirements in AMS 2249C specification.6 Product analysis tolerancelimits do not broaden the specified heat analysis requirements butcover variations between laboratories in the measurement of chemicalcontent.

Hydrogen content must be kept very low in Ti-6Al-7Nb alloy to avoidhydrogen embrittlement. Hot working operations in the titanium millare typically performed in air and this can increase the hydrogencontent because of the reactive nature of the alloy at elevated temper-ature. Surface protective coatings and special thermal treatments areused to minimize the pick-up of residual hydrogen during high temper-ature processing. Ti-6Al-7Nb cleaning operations which use nitric

plus hydrofluoric acid solutions are carefully controlled to eliminatehydrogen absorption during pickling. A ratio of 10 parts nitric acid to 1part hydrofluoric acid is recommended.7 Hydrogen analysis is typicallyperformed on the finish mill product after all high temperature andcleaning operations have been completed.


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2. Microstructure

The room temperature microstructure of Ti-6Al-7Nb consists of a dual

phase alpha + beta structure that is similar to Ti-6Al-4V alloy. An alpha+ beta globular microstructure is typically obtained for Ti-6Al-7Nb alloyafter solution annealing at 700 C, 1 hour, air cool or water quench.1

Hot pressing studies 8 have shown that Ti-6Al-7Nb alloy compositionswith 6.0% to 7.0% niobium contain 10% to 12% beta phase.This is comparable to Ti-6Al-4V alloy which contains 9% to 12.5%beta phase.

The temperature at which the alpha-beta phase transformation occurs

is known as the beta transus. A beta transus of 1010 C 15 C hasbeen reported for Ti-6Al-7Nb alloy.1 The actual beta transus tempera-ture is dependent on composition and, hence, can be used as a meas-ure of compositional uniformity. Optimized heat treating operationsmay also be established on the basis of beta transus temperature.

The alpha + beta microstructure of hot rolled and annealed Ti-6Al-7Nbbar is shown in the following transverse photomicrograph at 200Xmagnification. The photomicrograph was provided by Dr. L. Zardiackas,

Division of Biomaterials, University of Mississippi Medical Center.

Annealed bar microstucture

Basic Metallurgy continued

ASTM F 1295 microstructure requirements specify a fine dispersion ofalpha+ beta phases resulting from processing in the alpha plus betafield. No alpha case, coarse elongated alpha platelets, or continuousalpha network at prior beta grain boundaries are permitted. ISOrequirements specify that the material must meet micrographs A1 to

A9 in ETTC 2 standard 9 for annealed material.


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The density of Ti-6Al-7Nb is nearly identical to Synthes unalloyedtitanium and Ti-6Al-4V. Titanium implants weigh about 45% of 316L

stainless steel and cobalt base implants 10 and this may represent a pa-tient comfort factor especially when large-sized devices are compared.

Modulus of elasticity is a physical property that describes the stress perunit strain in the elastic region. A low modulus of elasticity is desirablebecause stress shielding is minimized and increased stress will be trans-ferred to the bone. The relative importance of stress shielding increasesas the size of the implant increases. The modulus of elasticity ofTi-6Al-7Nb, Ti-6Al-4V, and unalloyed titanium are similar and the

values are significantly lower than 187 GPa for 316L stainless steeland 248 GPa for cast Co-Cr-Mo biomaterials.10

The magnetic permeability of low permeability materials may bemeasured with an instrument known as a High Sensitivity Low-MuPermeability Indicator or Severn Gauge.11 The lowest calibratedmeasurement probe is equal to 1.01. Magnetic permeabilities ofless than 1.01 have been recorded 12 for Ti-6Al-7Nb alloy. The titaniumalloy demonstrates negligible residual magnetism and Ti-6Al-7Nb

implants may be routinely scanned with Magnetic ResonanceImaging equipment.13

5

1. Physical

The physical properties of Ti-6Al-7Nb1 have been compared to

unalloyed titanium Grade 1 through Grade 4 and Ti-6Al-4V alloy.10

Properties

Density Modulus of elasticityMaterial (gm/cc) in tension (GPa)

Ti-6Al-7Nb 4.52 105

Ti-6Al-4V 4.43 114

Ti Grade 1 4.51 103

Ti Grade 2 4.51 103

Ti Grade 3 4.51 103

Ti Grade 4 4.51 104


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Properties continued

6

The minimum UTS (Ultimate Tensile Strength) and minimum 0.2% Y.S.(Yield Strength) of Ti-6Al-7Nb is similar to Ti-6Al-4V ELI alloy andsignificantly higher than Ti Grade 4. The minimum % elongation forboth titanium alloys is less than Ti Grade 4 and this is expected, be-cause of the significantly higher strength characteristics. The minimum% reduction of areas are identical. Mechanical property limits indicatethese titanium materials have similar levels of tensile ductility.

A mechanical test known as a notched tensile test is commonly used

to evaluate the relative notch sensitivity of various materials. The test isperformed by comparing the tensile strength of a notched crosssection to a smooth cross section. The notch is produced by precisionmachining a bar specimen so that the notch geometry matches aspecific factor of stress concentration (Kt). Notched tensile results fora Kt value of 3.2 have been reported by S. Steinemann

14 as follows:

Minimum tensile properties for bar in the annealed condition

Min.

Min. Min. Min. Reduction

ASTM UTS 0.2% y. S. Elong. in area**

Material Spec. (MPa) (MPa) (%) (%)

Ti-6Al-7Nb F 1295 900 800 10* 25

Ti-6Al-4VELI F 136 860 795 10** 25

Ti Grade 4 F 67 550 483 15** 25

* gage length = 5.65 X S, where S is the original cross-sectional area, in mm** gage length = 4D, where D is the machined diameter in mm

2. Tensile

Minimum tensile properties for Ti-6Al-7Nb bar up to 100 mm diameter,

Ti-6Al-4V ELI bar from 4.75 to 44.45 mm in diameter or thickness, andcommercially pure unalloyed titanium Grade 4 bar have beencompared as follows:

NTS UTSMaterial Condition (MPa) (MPa) NTS/UTS

Ti-6Al-7Nb Annealed 1387 1024 1.35

Ti-6Al-4V Annealed 1598 1076 1.49

Ti Grade 4 Cold Worked 1387 785 1.77

Notch tensile sensitivity of titanium materials


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Materials which have a NTS/UTS ratio of 1.10 or greater in this testare classified as notch insensitive, i.e. they are not notch sensitive.

Results clearly demonstrate that Ti-6Al-7Nb along with Ti-6Al-4V andTi Grade 4 are not considered notch sensitive materials when evaluatedaccording to notch tensile strength criteria.

3. Fatigue

M. Semlitsch and the group at Sulzer 8 have reported the rotatingbending fatigue strength of shot peened Ti-6Al-7Nb alloy in varioushot worked conditions.

700

650

600

550500

450

400

350

300

FatigueStrength(MPa)

Extrudedand Forged

Pressedand Forged

Hot Rolled

The fatigue strength increases as the total amount of hot deformation increases. This isrelated to the homogeneous structure and grain refinement that result from cumulativehot working operations. Hot rolled Ti-6Al-7Nb bar typically has a fatigue strength in ex-cess of 50% of the ultimate tensile strength which is very desirable for a titanium alloy.

Rotating bending fatigue tests 14 have also been performed with 5.68 mm round hour-glass shaped specimen at 6,000 rpm. Samples were prepared by vibratory finishingfollowed by electropolishing. Comparative results generated in this series of fatiguetests showed the following trends:

Rotating bending fatigue strength of hot worked Ti-6Al-7Nb


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Stress Amplitude (MPa)at Specified Cycles

The stress amplitude at 10 7 cycles is known as the endurance limit.This is the maximum stress below which a material can presumably

endure an infinite number of stress cycles. The Ti-6Al-7Nb endurancelimit is equivalent to Ti-6Al-4V alloy and is substantially better thancold worked Ti Grade 4.

4. Corrosion

Polarization curves 15 in 2 molar hydrochloric acid at 37 C are shownin the following diagram.


The unalloyed titanium and Ti-6Al-7Nb exhibit a classic active-passivetransition at -500 mV with stable passive behavior up to at least +3000mV. The very similar anodic polarization curves for Ti-6Al-7Nb andunalloyed titanium also suggest that galvanic corrosion would not beexperienced. Unalloyed titanium and Ti-6Al-7Nb resist breakthrough

Material Condition 104 107 >10

Ti-6Al-7Nb Annealed 810 540 540

Ti-6Al-4V Annealed 540 540

Ti Grade 4 Cold Worked 670 430 430

Fully reversed rotating fatigue

-500 0 1000 2000 3000 4000 5000 6000 7000

103

102

101

Millivolts vs. SCE

Pitting Potential

Active/PassiveTransition

Ti6Al4VTiTi6Al7Nb

A/cm2


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but not Ti-6Al-4V, which exhibits a strong current increase for a pittingpotential of 6000 mV. Anodic polarization results confirm the improved

corrosion resistance of Ti-6Al-7Nb when compared to Ti-6Al-4V in areducing acid environment.

Pitting potential results 16 versus a Saturated Calomel Electrode (SCE) ina severe reducing acid environment of 2 molar HCl at 37 C are shownin the following graph.

Breakthrough results indicate that the pitting potential of Ti-6Al-7Nbis above +10.0 volts which is identical to unalloyed titanium andsubstantially better than the + 5.9 volts exhibited by Ti-6Al-4V alloy.

This suggests that the Ti-6Al-7Nb passive film is more resistant tobreakdown than the Ti-6Al-4V in an aggressive reducing acidenvironment.

The corrosion fatigue strengths of Ti-6Al-7Nb and Ti-6Al-4V totalhip stems 17 have been compared by Semlitsch. Corrosion fatiguestrengths were similar when tested for 5 million cycles in Ringerssolution at 37 C and a frequency of 6 Hertz.

Exposure of Ti-6Al-7Nb alloy to sodium chloride, ferric chloride, and

amino acids 18 have shown that the alloy is chemically inert under thetest conditions investigated.

Samples have also been tested by four-point bend testing at 80% ofthe 0.2% Y.S. in NACE TM0177-86 solution for 760 hours.19 The testsolution is very aggressive and contains sodium chloride, glacial aceticacid, and is saturated with bubbling hydrogen sulfide.

10

8

6

4

2

0

PittingPotential(+ volts)

Ti6Al7Nb Ti6Al4V Ti

>10.0 >10.0

5.9

Pitting potential in 2 molar HCI at 37C


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5. Biocompatibility

In vitro organ culture tests evaluated the growth inhibition of organ

cultured embryonic rat femurs in the presence of soluble metalchlorides for 10 days and solid metal implants for 7 days.20 Resultsindicated that vanadium salts are an order of magnitude more toxicthan nickel, cobalt, and copper salts. The same experiments were alsoperformed with niobium and aluminum oxide salts that were saturatedin the test electrolyte. No toxic reactions occurred.21

No growth inhibition was observed in femurs with niobium andtitanium metal wire implants.20 These metals were well tolerated as

evidenced by the appearance of normal cartilage cells near the wire im-plants. However, other metals such as nickel, cobalt, copper, and ironshowed marked corrosion, growth inhibition, and cell damage. Alu-minum metal was not tested in this study.

Work at Lausanne University, Institute for Experimental Physics, 22 hasconcluded that the oxides or hydroxides of Ti, Al, and Nb are atsaturation in biological tissue. The dissolved metals will not be ionizedor transported in vivo. The elements in Ti-6Al-7Nb do not create a

bioburden and this accounts for the excellent localized biocompatibilityobserved for this alloy.

In vivo screening tests 23 were performed with grooved cylindersimplanted subcutaneously in the backs of mice for 1, 3, and 9 weeks.This test is identical to the subcutaneous screening method specifiedin ASTM F 1408.24 Histological analysis revealed that the Ti-6Al-7Nbimplants did not create adverse tissue tolerance reactions. The numberof giant cell nuclei was smaller for vanadium-free alloys.

Synthes bone screws machined from unalloyed titanium and varioustitanium alloys were implanted in dog femora for up to 2 years. 25

Testing was performed according to ASTM F 981 standard.26 Histologi-cal evaluation indicated that direct bone attachment was observedat the Ti-6Al-7Nb bone screw surface. Overall biocompatibility resultswere excellent with no adverse cellular reactions observed histologi-cally. Removal torques at 26 and 52 week retrieval periods were similarfor anodized screws fabricated from Ti-6Al-7Nb and Ti-6Al-4V. Allunalloyed titanium and titanium alloy screws evaluated in the study

demonstrated similar removal torque from dog femora bone.

Mechanically polished Ti-6Al-7Nb discs implanted in the backs of mice 27

were retrieved for histological and surface chemistry analysis at theUniversity of Lausanne. Desorption studies indicated that the amountof adherent soft tissue was similar for Ti-6Al-7Nb and unalloyed


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titanium implants. Visible corrosion products were not present on thesurface of the implants after the surrounding tissue was removed.

Retrieval analyses of human hip joint prostheses 28 have concludedthat Ti-6Al-7Nb is extremely biocompatible as evidenced by osseousingrowth at the implant surface. Histological examination indicatedthat osseous tissue formation along the entire stem length providedsecondary implant stabilization.

6. Surface

The surface oxide of Ti-6Al-7Nb has been characterized 18 by X-RayPhotoelectron Spectroscopy analysis. The surface study found the oxide

film was a mixture of TiO2, Al2O3, and Nb2O5. This study concluded thatthe mixed oxide film formed on Ti-6Al-7Nb alloy is more chemicallystable than the TiO2 oxide layer formed on unalloyed titanium.

Ti-6Al-7Nb implants may be shot peened for improved fatigue life butthe shot peening media must be carefully selected to avoid iron con-tamination at the surface of the implant. Final surface treatment aftermachining, or after machining and shot peening, consists of electro-chemical anodizing, although nitric acid passivation may also be used.29

Synthes Ti-6Al-7Nb implants have an anodized surface finish that isproduced by immersing the implants in an electrochemical solution fora specified time and voltage. The color that is produced is a functionof the mixed oxide film thickness which is controlled in the anodizingprocess. Visible light diffraction within the oxide produces a distinctcolor. No pigments or organic coloring agents are present in theanodized film. The standard Synthes anodizing treatment creates agold appearance that is a distinguishing feature of Synthes titanium

implants. The anodizing process is capable of creating a variety ofcolors, depending on the thickness of the oxide film.

Surface analysis of anodized CP titanium 30 has shown that typicalanodizing treatments increase the oxide thickness and alter theoxide chemistry. Corrosion studies concluded that the anodized filmexhibited reduced corrosion rates when compared to unanodizedspecimens. Extrapolation of the CP titanium results suggest thatanodizing improves the corrosion resistance of the mixed oxide filmthat is normally present on the surface of Ti-6Al-7Nb alloy.

Recent studies in aerated 3% sodium chloride 31 indicated thatanodized films on Ti-6Al-7Nb and other titanium alloys have higher po-larization resistance than CP titanium. The results confirmed increasedstability and better corrosion resistance for an anodized oxide film ina chloride-containing corrosive environment.



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1. Surgical Implant Alloy IMI 367, Product Bulletin, IMI TitaniumLimited, Birmingham, England.

2. Steinemann, S., and Perren, S., Surgical Implant and Alloy forUse in Making an Implant, U.S. Patent 4,040, 129, August 9,1977.

3 Niobium, Product Brochure, Teledyne Wah Chang, Albany, OR,pp. 3-4.

4. ISO 5832-11: Implants for Surgery Metallic Materials, Part II:Wrought Titanium-6 Aluminum-7 Niobium Alloy, InternationalOrganization for Standardization.

5. ASTM F 1295: Standard Specification for Wrought Titanium-6Aluminum-7 Niobium Alloy for Surgical Implant Applications,American Society for Testing and Materials, Philadelphia, PA.

6. AMS 2249C: Chemical Check Analysis Limits, Titanium and Tita-nium Alloys, Society of Automotive Engineers, Warrendale, PA.

7. ASTM B 600, Standard Recommended Practices for Descalingand Cleaning Titanium and Titanium Surfaces, American Society

for Testing and Materials, Philadelphia, PA.8. Semlitsch, M., et.al., Titanium-Aluminum-Niobium Alloy,

Development for Biocompatible High Strength Surgical Im-plants, Sonderduck aus Biomedizinische Technik 30, (1985), 12,S. 334-339.

9. Technical Committee of European Titanium Producers, ETCC2Monograph, IMI Titanium Ltd., Birmingham, England, KynochPress.

10. Disegi, J., AO/ASIF Unalloyed Titanium Implant Material,Second Edition, AO/ASIF Technical Publications, SYNTHES (USA),July 1991.

11. Severn Engineering Company, Inc., Annapolis, MD.

12. Disegi, J., Internal Correspondence, SYNTHES (USA), Paoli, PA.

13. Disegi, J., Magnetic resonance imaging of AO/ASIF stainlesssteel and titanium implants, Injury, AO/ASIF Scientific Supple-

ment, Vol. 23, Supplement 2, 1992.14. Steinemann, S., et.al., Beta-Titanium Alloy for Surgical

Implants, Seventh World Conference on Titanium, San Diego,CA, June 28-July 2, 1992.

15. Protasul 100 (Ti-6Al-7Nb) Vanadium-Free, High Strength Tita-nium Alloy, Technical Report, Protek, Inc., Indianapolis, IN, 1988.

References


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16. Simpson, J., The Electrochemical Behavior of Titanium andTitanium Alloys With Respect to Their Use as Surgical Implant

Materials, Biological and Biomechanical Performance of Bioma-terials, Elsevier Science Publishers, Amsterdam, pp. 63-68, 1986.

17. Semlitsch, M., et.al. Development of a Vital, High-StrengthTitanium-Aluminum-Niobium Alloy for Surgical Implants,Biological and Biomechanical Performance of Biomaterials,Elsevier Science Publishers, Amsterdam, pp. 69-74, 1986.

18. Maeusli, P., et.al., Surface Characterization of Titanium andTi-Alloys, Biological and Biomechanical Performance of Bioma-

terials, Elsevier Science Publishers, Amsterdam, pp. 57-62, 1986.

19. Simpson, J., Re: ASTM-Norm Titanium Alloy Ti-6Al-7NbInternal Report, Sulzer Innotec, Winterthur, February 3, 1990.

20. Gerber, H., and Perren, S., Evaluation of Tissue Compatibility ofin vitro Cultures of Embryonic Bone, Evaluation of Biomaterials,John Wiley and Sons, pp. 307-314, 1980.

21. Gerber, H., et.al., Bioactivity of metals: Tissue tolerance of

soluble solid metal tested on organ cultured embryonic bonerudiments, Technical Principles, Design and Safety of Implants,G.H. Buchhorn, H.G. Wiliert (eds.), Hogrefe & Huber,Toronto/Bern.

22. Steinemann, S., and Maeusli, P., Titanium Alloys for Surgical Im-plants Biocompatibility from Physiochemical Principles, SixthWorld Conference on Titanium, France, pp. 535-540, 1988.

23. Perren, S., et.al, Quantitative Evaluation of Biocompatibility of

Vanadium Free Titanium Alloys, Biological and BiomechanicalPerformance of Biomaterials, Elsevier Science Publishers,Amsterdam, pp. 397-402, 1980.

24. ASTM F 1408: Practices for Subcutaneous Screening Test forImplant Materials, American Society for Testing and Materials,Philadelphia, PA.

25. Olmstead, M., and Pohler, O., Report on Long TermCompatibility Testing of New Titanium Alloys, AO Research

Grant 1987/88, Stratec Medical, Waldenburg, January 17, 1990.26. ASTM F 981: Assessment of Compatibility of Biomaterials (Non-

porous) for Surgical Implants with Respect to Effect of Materialson Muscle and Bone, American Society for Testing and Materials,Philadelphia, PA.

27. Gold, J., et.al., XPS Study of Retrieved Titanium and Ti Alloy

References continued


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Implants, Advances in Biomaterials, Volume 9, Clinical ImplantMaterials, Heimke, G., ed., Elsevier Science Publishers,

Amsterdam, pp. 69-74, 1990.28. Zweymuller, K., et.al., Biologic Fixation of a press-Fit Titanium

Hip Joint Endoprosthesis, Clinical Orthopaedics, Volume 235,pp. 195-206, October 1988.

29. Solar, R., et.al., Titanium Release from Implants: A ProposedMechanism, Corrosion and Degradation of Implant Materials,ASTM STP 684, B. Syrett and A. Acharya, American Societyfor Testing and Materials, Philadelphia, PA, p. 172, 1979.

30. Lucas, L., et.al., Corrosion and Auger Surface ChemistryAnalyses of Surface Modified Porous Titanium, Transaction ofthe 17th Annual Society for Biomaterials, p. 201,May 1-5, 1991.

31. Frey, N., et.al., Properties of Surface Oxides on Titanium andSome Titanium Alloys, Seventh World Conference on Titanium,San Diego, CA, June 28-July 2, 1992.


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ALLOY. A metallic substance composed of two or more elements atleast one of which is metal.

ALLOYING ELEMENT. An element, added to and remaining in ametal, that changes the metals structure and properties.

ALPHA. The low temperature form of titanium with a hexagonalclose-packed (hcp) crystal structure.

ALPHA + BETA STRUCTURE. A microstructure containing alphaand beta as the principal phases at ambient temperatures.

ALPHA CASE. The oxygen, nitrogen, or carbon enriched alpha

stabilized surface resulting from elevated temperature exposure.ANNEALING. A metal softening operation in which the metal isheated to and held at a specified temperature, followed by cooling ata controlled rate.

ANODIC REACTION. An oxidation reaction that produces electronsat the anode of an electrochemical cell. When dissimilar metals arecoupled, the anode usually experiences increased corrosion.

ANODIZING. An electrolytic process that increases the thicknessof the protective oxide film on titanium.

BETA. The high temperature form of titanium with a body-centeredcubic (bcc) crystal structure.

BETA TRANSUS. The minimum temperature at which 100% betaphase can exist.

BODY-CENTERED CUBIC. A unit cell which consists of atomsarranged at cube corners with one atom at the center of the cube.

BRITTLENESS. The tendency of a material to fracture without firstundergoing significant permanent deformation.

CATHODIC REACTION. A reduction reaction that consumeselectrons at the cathode of an electrochemical cell. When dissimilarmetals are coupled, the cathode usually undergoes reduced corrosion.

COLD-WORKED MICROSTRUCTURE. A microstructure resultingfrom cold working the material.

COLD WORKING. Permanently deforming a metal or alloy at roomtemperature to increase its strength.

CRYSTAL. A solid composed of atoms that repeat in a pattern ofregular intervals in three dimensions.

Glossary


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DESCALING. Chemically or mechanically removing the thick oxidelayer that is formed on metals during high temperature processing.

DUCTILITY. The ability to permanently deform before fracturing.

ELECTRODE. A cylindrical metal compact that is suitable for vacuumarc melting or a metal ingot that is suitable for remelting.

ELONGATED ALPHA. A fibrous type of microstructure that resultsfrom unidirectional cold working of unalloyed titanium.

ELONGATION. A term that describes ductility by measuring theamount of extension that a material undergoes during tensile testing.

EQUIAXED STRUCTURE. A microstructure feature that consists ofpolygonal shaped grains with equal dimensions in all directions.

FATIGUE. The phenomenon leading to fracture under repeated orfluctuating stresses having a maximum value less than the ultimatetensile strength of the material.

FATIGUE LIFE. The number of cycles of stress or strain of a specifiedcharacter that a given specimen sustains before failure of a specificnature occurs.

FATIGUE STRENGTH. The maximum stress that can be sustained fora specified number of cycles without failure, the stress being completelyreversed within each cycle unless otherwise stated.

FRETTING CORROSION. An accelerated form of corrosion thatcan occur when the protective passive film is mechanically abraded.The relative motion of the underside of a bone screw head with thecontact surface of a bone plate is a typical example.

GPa. Gigapascal equals 1000 MPa.HEXAGONAL CLOSE-PACKED. A unit cell which consist of ahexagonal arrangement of atoms in a plane surrounding an atomfollowed by three atoms in the next horizontal plane.

HOT-WORKED MICROSTRUCTURE. A microstructure resultingfrom hot working the material.

HOT WORKING. Permanently deforming metal at an elevatedtemperature that is usually above recrystallization temperature.

INCLUSION. A particle of foreign material in a metallic microstructurethat is usually considered undesirable.

INGOT. A metal casting that is suitable for remelting or hot working.


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Glossary continued

INTERMETALLIC COMPOUND. A phase in an alloy system thathas a well-defined composition and limited solubility.

LONGITUDINAL. Parallel to the principal direction of hot or coldworking.

MASTER ALLOY. An alloy rich in one or more elements that isadded to a melt to raise the percentage of a desired constituent.

MICROSTRUCTURE. The structure of metals as revealed bymicroscopic examination of a specimen.

MODULUS OF ELASTICITY. A measure of the stress per unit strain

in the elastic region before permanent deformation occurs.PASSIVATION. The process of changing the chemical activity of ametal surface to a less reactive state, usually to increase the corrosionresistance.

PICKLING. Chemical removal of the thick oxide layer that is formedon metals during high temperature processing.

POLYGONAL STRUCTURE. A closed planar shape bound onat least three sides.

RECRYSTALLIZATION. A change from one crystal structure toanother that occurs during heating or cooling through a criticaltemperature range.

REDUCTION IN AREA. A tensile testing measure of ductility thatequals the original area minus the area after fracture divided by theoriginal area, expressed as a percentage.

SOLUBILITY. A measure of the amount of a substance that can be

dissolved in a metal or alloy.STRAIN. Change in length per unit length in the direction of theapplied stress.

STRESS. Forcer per unit area.

STRESS CORROSION CRACKING. Failure of metals by crackingunder combined action of corrosion and stress.

TRANSVERSE. Perpendicular to the principal direction of hot or

cold working.TWINNING. A microstructure feature that describes mirror-imagepositions across a planar interface.


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ULTIMATE TENSILE STRENGTH. In tensile testing, the maximumload at fracture divided by the original cross-sectional area.

UNALLOYED TITANIUM. Single phase titanium metal that doesnot contain major alloying additions.

VACUUM ARC REMELTING. A melting process in which anelectric arc is used to remelt an electrode inside a vacuum chamber.

YIELD STRENGTH. In tensile testing, the stress at which thestress-to-strain ratio exhibits a specified deviation, usually designatedas 0.2% offset.


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1993 Synthes, Inc. or its affiliates. All rights reserved. Synthes is a trademark of Synthes, Inc. or its affiliates.

Synthes (USA)1302 Wrights Lane EastWest Chester, PA 19380Telephone: (610) 719-5000

www.synthes.com

Implant Materials Titanium 6_ Aluminum 7_ Niobium

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