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Journal of Alloys and Compounds 479 (2009) 699–703

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

journa l homepage: www.e lsev ier .com/ locate / ja l l com

lectrochemical characterization of �-Ti alloy in Ringer’s solution formplant application

atendra Kumar ∗, T.S.N. Sankara Narayanan ∗

ational Metallurgical Laboratory, Madras Centre CSIR Complex, Taramani, Chennai 600 113, India

r t i c l e i n f o

rticle history:eceived 16 June 2008eceived in revised form 6 January 2009ccepted 15 January 2009vailable online 20 February 2009

eywords:itanium alloysorrosion behaviour

a b s t r a c t

The corrosion behaviour of Ti–15Mo alloy in Ringer’s solution was evaluated by potentiodynamic polar-ization, cyclic polarization and chronoamperometric/current–time transient (CTT) studies. The corrosionprotective ability of Ti–15Mo alloy was compared with that of commercially pure (CP) titanium (grade-2) and Ti–6Al–4V alloy under similar experimental conditions. The microstructure, microhardness andstructural characteristics were also evaluated to ascertain the suitability of these materials for orthopaedicimplant applications. The study reveals that Ti–15Mo alloy possesses a �-phase microstructure andmoderate hardness. The open circuit potential of Ti–15Mo alloy is relatively nobler than CP–Ti andTi–6Al–4V alloy. The average passive current density of all the three Ti materials studied lies in the rangeof 32 × 10−6 A/cm2. The passivation range of Ti–15Mo alloy is relatively large when compared to that of

-ray diffraction

lectrochemical characterizationiomedical applications

Ti–6Al–4V alloy and CP–Ti. The loop area of the cyclic polarization curve of Ti–15Mo alloy is quite similarto that of Ti–6Al–4V alloy but relatively smaller than that of CP–Ti. There is no appreciable variation inthe steady state current density of all the three Ti materials measured at +0.5 V vs. SCE whereas a signifi-cant variation is observed at +1.25 V vs. SCE. Based on the �-phase structure, moderate hardness and theability to offer a better corrosion resistance in Ringer’s solution, Ti–15Mo alloy can be used as a suitablealternative material for orthopaedic implant applications.

. Introduction

Titanium and titanium alloys are widely used for many biomedi-al applications due to their low density, excellent biocompatibility,orrosion resistance and mechanical properties [1–4]. Among thearious types of Ti alloys, Ti–6Al–4V alloy has been the choicen many instances. However, studies have expressed concernsn the use of this alloy in spite of the fact that the mechanicalroperties and corrosion resistance of Ti–6Al–4V alloy are ideal for

mplant applications. The two major concerns are: (i) the leachingf V and Al that could cause long term health problems suchs peripheral neuropathy, osteomalacia and Alzheimer diseases5]; and (ii) the large modulus mismatch between the Ti–6Al–4Vlloy (∼110 GPa) and the bone (∼10–40 GPa), which could causensufficient loading on bone adjacent to the implant, leading to an

ventual failure of the implant [6]. The high modulus of Ti–6Al–4Vlloys is attributable to the high volume fraction of the �-phasen them. Since the �-phase in Ti alloys exhibits a significantlyower modulus than the �-phase, development of lower modulus

∗ Corresponding authors. Tel.: +91 44 2254 2077; fax: +91 44 2254 1027.E-mail addresses: sat nml@rediffmail.com (S. Kumar), tsnsn@rediffmail.com

T.S.N. Sankara Narayanan).

925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.jallcom.2009.01.036

© 2009 Elsevier B.V. All rights reserved.

�-Ti alloys, which retain a single �-phase microstructure on rapidcooling from high temperatures, assumes significance. Several�-phase Ti alloys, using Nb, Ta and Mo as alloying elements(�-stabilizers), such as Ti–12Mo–6Zr–2Fe, Ti–13Mo–7Zr–3Fe(‘TMZF’), Ti–15Mo–5Zr–3Al, Ti–15Mo–3Nb–3O (‘TIMETAL 21Srx’),Ti–14Nb–13Zr, Ti–35Nb–7Zr–5Ta, Ti–34Nb–9Zr–8Ta (‘TNZT’),Ti–29Nb–4.6Zr–13Ta, Ti–15Mo, Ti–12Mo–5Ta, Ti–25Nb–3Fe, etc.[6–12] were developed.

Ho et al. [6], Nag et al. [13], Ho [14] and Oliveira et al. [15] havestudied the structure and properties of a series of binary Ti–Mo alloywith Mo content ranging up to 20 wt.%. Based on the microstruc-tural evolution and strengthening mechanisms, Nag et al. [13] haverecommended Ti–15Mo alloy as one of the promising biocompat-ible Ti alloy. The corrosion behaviour of Ti–Mo alloys in simulatedbody fluid and dental environment was studied earlier [15–22].Oliveira et al. [15] have evaluated the corrosion behaviour of a seriesof Ti–Mo alloys with 4–20 wt.% Mo content in Ringer’s solution.According to them increase in Mo content of the Ti–Mo alloy enablesan improvement in the corrosion protective ability. Oliveira et al.

[15] and Oliveira and Guastaldi [19,20] have reported that Ti–Moalloys having 4–20 wt.% Mo exhibit spontaneous passivation inRinger’s solution and do not exhibit pitting even at very high poten-tials, up to 8 V (vs. SCE). Based on their ability to exhibit spontaneouspassivation, electrochemical stability of the passive films and bet-

700 S. Kumar, T.S.N. Sankara Narayanan / Journal of A

Table 1Chemical composition of the Ti materials used in this study.

Element CP–Ti (grade 2) Ti–6Al–4V alloy Ti–15Mo alloy

N 0.01 0.02 0.01C 0.03 0.03 0.02H 0.010 0.011 0.011Fe 0.20 0.22 0.012O 0.18 0.16 0.10Al – 6.12 –VMT

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i Balance Balance Balance

er biocompatibility, Oliveira and Guastaldi [19,20] have suggestedhat Ti–Mo alloys can be used as a biomaterial. Alves et al. [17]ave evaluated the corrosion resistance of Ti–10Mo alloy in fluori-ated physiological serum (0.15 M NaCl + 0.03 M NaF [pH = 6]) andompared with that of Ti–6Al–4V alloy. The corrosion behaviour ofi–15Mo alloy in 0.15 M NaCl solution containing varying concen-rations of fluoride ions (190, 570, 1140 and 9500 ppm) was studiedecently by Kumar and Sankara Narayanan [18] for dental implantpplications. Karthega et al. [21] have reported that the corrosionesistance of Ti–15Mo and Ti–29Nb–13Ta–4.6Zr (TNTZ) (� titaniumlloys) in Hank’s solution are almost similar. Based on the corrosionrotective ability Capela et al. [22] have ranked the Ti–Mo alloys asollows: CP–Ti > Ti–6.5Mo > Ti–8.5Mo > Ti–10Mo. The present studyims to evaluate the corrosion resistance behaviour of Ti–15Molloy in Ringer’s solution and, to compare its corrosion protectivebility with that of commercially pure (CP) titanium (grade 2) andi–6Al–4V alloy under similar conditions, to ascertain the suitabil-ty of Ti–15Mo alloy for orthopaedic implant applications.

. Experimental details

Commercially pure titanium (grade 2) and, Ti–6Al–4V and Ti–15Mo alloys weresed in this study. The chemical composition of these Ti materials is given in Table 1.or microstructural evaluation, the Ti materials were mechanically polished usingarious grades of SiC paper and finally using a 0.3-�m diamond paste. The polishedpecimens were then etched using a HNO3–HF mixture (15 vol.% HNO3; 5 vol.% HF;0 vol.% water) for 30 s, rinsed in deionized water and dried. The microstructure of Tiaterials was examined using a Leica DMLM optical microscope with image analyzer

oftware. The structural characteristics of the three Ti materials were evaluated by-ray diffraction (XRD) measurement. The hardness of Ti materials was determinedsing a Leica VMHTMOT microhardness tester with a Vickers diamond indenternder a load of 200 g. The lap time for each indentation was 15 s and the valueseported represent the average of five measurements.

The corrosion behaviour of CP–Ti, Ti–6Al–4V and Ti–15Mo alloys was studied byotentiodynamic polarization, cyclic polarization and chronoamperometric/

urrent–time transient (CTT) studies using a Potentiostat/Galvanostat of ACM instru-ents (Model: Gill AC) and a flat cell (Wear and Friction Tech, Chennai, India).

inger’s solution having a chemical composition (in g/l) of 9 NaCl, 0.24 CaCl2, 0.43Cl and 0.2 NaHCO3 (pH: 7.8) [23] in non de-aerated condition was used as thelectrolyte. Before conducting the corrosion studies, all the three Ti materials wereechanically polished using various grades of SiC paper, rinsed with deionized

Fig. 1. Microstructure of the Ti alloys: (a) CP–Ti;

lloys and Compounds 479 (2009) 699–703

water, pickled using a HNO3–HF mixture (35 vol.% HNO3; 5 vol.% HF; 40 vol.% water)at 40 ◦C for 60–70 s [24], rinsed in deionized water and dried using a stream of com-pressed air. The cleaned Ti samples were placed inside a flat cell so that only 1 cm2

area of the sample was exposed to the Ringer’s solution. The Ti samples forms theworking electrode. A saturated calomel electrode (SCE) and a graphite rod wereused as the reference and counter electrodes, respectively. All experiments wereconducted at 37 ± 1 ◦C.

Before conducting the potentiodynamic or cyclic polarization studies, the threeTi materials were immersed in Ringer’s solution for 1 h for stabilization and theiropen circuit potentials (OCP) were measured during this period. Potentiodynamicpolarization tests were performed at a scan rate of 100 mV/min. Both in the cathodicand anodic directions, from their respective open circuit potential. In the cathodicdirection, the potential scan was limited to 250 mV whereas in the anodic directionthe potential was scanned up to 3000 mV from their respective OCP. Cyclic polariza-tion study in Ringer’s solution was also performed to compare the pitting corrosionresistance of all three Ti materials used in present study. During cyclic polarizationstudy, the potential of the samples was reversed after reaching an anodic potentialof +2000 mV vs. SCE with respect to their respective OCP. CTT studies of all the threeTi materials in Ringer’s solution were performed at +0.50 and +1.25 V vs. SCE for thetime duration of 90 min. The potentiodynamic polarization, cyclic polarization andCTT studies were repeated at least three times so as to ensure reproducibility of testresults.

3. Results and discussion

3.1. Microstructure

The microstructure of CP–Ti, Ti–6Al–4V and Ti–15Mo alloys areshown in Fig. 1(a)–(c), respectively. The microstructure of CP–Ti(Fig. 1(a)) exhibits a typical rapidly cooled metastable feather-like microstructure that consists of equiaxed �-grain with sometwin bands. The microstructure of Ti–6Al–4V reveals �–� structure(Fig. 1(b)) that consists of elongated �-grains (light) and inter-granular �-grains (mottled or outlined). In case of Ti–15Mo alloy(Fig. 1(c)) equiaxed �-grains is observed as the dominant phase.The grains are homogeneous and evenly distributed. Ho et al. [6]have reported that Ti–Mo alloys having 9 wt.% Mo have a signifi-cant amount of equiaxed �-phase and in alloys containing ≥10 wt.%Mo; the �-phase became the only dominant phase. Davis et al. [25]have also suggested the retention of �-phase at higher Mo content.Bania [26] has reported that a minimum of 10 wt.% Mo is requiredto fully stabilize the �-phase at room temperature. The presence of15 wt.% Mo makes the �-phase as the only dominant phase in themicrostructure of the Ti–15Mo alloy (Fig. 1(c)) and supports theobservations made by other researchers [6,25,26].

3.2. Structural characteristics

The X-ray diffraction pattern of CP–Ti, Ti–6Al–4V and Ti–15Moalloys are shown in Fig. 2(a)–(c), respectively. It is evident from Fig. 2that the XRD pattern of CP–Ti is comprised entirely of hexagonal �′-phase; the Ti–15Mo alloy exhibits the presence of only the �-phasewhereas the Ti–6Al–4V alloy exhibits the presence of both �- and

(b) Ti–6Al–4V alloy; and (c) Ti–15Mo alloy.

S. Kumar, T.S.N. Sankara Narayanan / Journal of Alloys and Compounds 479 (2009) 699–703 701

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Table 2Passivation range, passive current density and pitting potentials of CP–Ti, Ti–6Al–4Vand Ti–15Mo materials in Ringer’s solution.

Type of Ti sample used Passivation range(mV) vs. SCE

Passive current density(1 × 10−6 A/cm2)

ig. 2. X-ray diffraction pattern of the Ti alloys: (a) CP–Ti; (b) Ti–6Al–4V alloy; andc) Ti–15Mo alloy.

-phases. The presence of only the �-phase for Ti–Mo alloys having10 wt.% Mo has also been reported earlier by Ho et al. [6].

.3. Microhardness

The average microhardness of CP–Ti, Ti–6Al–4V and Ti–15Molloys is found to be 175, 324 and 238HV0.2, respectively and theyre in agreement with the values reported elsewhere [6,13,27,28].mong them, the �-phase CP–Ti has the lowest microhardness and

he Ti–6Al–4V alloy with � + � phase posses the highest hardnesshile the hardness of Ti–15Mo alloy lies in between these two. Ho et

l. [6] have reported that the hardness of CP–Ti (156HV) is far lesshan that of Ti–12.5Mo alloy (340HV). Okasaki [28] has reportedhat the hardness of CP–Ti, Ti–6Al–4V and Ti–15Zr–4Nb–4Ta alloys�-phase Ti alloy) are in the range of 180, 340 and 330HV,espectively. Gordin et al. [11] have reported that the hardnessf Ti–6Al–4V and Ti–12Mo–5Ta alloys (�-phase Ti alloy) are 330nd 303HV, respectively. However, the hardness of Ti–20Mo alloys found be higher than that of Ti–6Al–4V alloy [6]. Based on theardness values reported in the literature and the values obtained

n the present study, it is clear that the hardness of Ti–Mo alloys is

igher than that of CP–Ti. However, compared to Ti–6Al–4V alloy,he hardness of Ti–Mo alloys appears to be influenced by the Moontent. As several factors might influence the microhardness of thei–Mo alloys, which include solid solution strengthening, precipita-ion hardening, strain aging, grain size and crystal structure/phase

ig. 3. Potentiodynamic polarization curves of CP–Ti, Ti–6Al–4V and Ti–15Mo alloysn Ringer’s solution (scan rate: 100 mV/min) (potential in mV vs. SCE).

CP–Ti grade 2 145–1522 32.0Ti–6Al–4V alloy 156–1460 32.4Ti–15Mo alloy 166–2513 32.4

(�, � + �, �) [6], predicting the extent of change in hardness onlywith the extent of Mo alloying is difficult.

3.4. Electrochemical characterization

3.4.1. Open circuit potential measurementThe Ti samples were immersed in Ringer’s solution for 1 h for sta-

bilization and the open circuit potential was measured during thisperiod. The OCP of CP–Ti and Ti–6Al–4V alloy is almost the similar,−520 and −516 mV vs. SCE, respectively, while the OCP of Ti–15Moalloy is −477 mV vs. SCE. The relatively nobler OCP of Ti–15Mo alloyindicates that it could offer a better corrosion resistance in Ringer’ssolution than CP–Ti and Ti–6Al–4V alloy. To get a better in sightabout the electrochemical corrosion behaviour of the Ti samples inRinger’s solution, potentiodynamic polarization, cyclic polarizationand chronoamperometric studies were performed.

3.4.2. Potentiodynamic polarization studiesThe potentiodynamic polarization curves of CP–Ti, Ti–6Al–4V

and Ti–15Mo alloys in Ringer’s solution, shown in Fig. 3, are quitesimilar. The anodic branch of the curves show a passive region asso-ciated with the formation of one or more protective films. For aclear analysis, the anodic portion of the curve is divided into twosegments; the potential region from −300 to +1200 mV vs. SCE assegment I whereas the potential region above +1200 mV vs. SCE assegment II. In segment I, passive current densities of all the threeTi materials are notably less whereas in segment II the passive cur-rent densities are relatively higher. In segment I, the polarizationcurves of CP–Ti and Ti–6Al–4V alloy overlap each other and theirpassive current densities are quite similar. However, the passive cur-rent density of Ti–15Mo alloy is relatively lower in this segment.Though segment II does not represent a clinical reality and therecould be a possible decomposition of the electrolyte, this segmentis considered here only to compare the range of passivation of thethree Ti materials in Ringer’s solution. The passivation range andaverage passive current density of CP–Ti, Ti–6Al–4V and Ti–15Moalloys are compiled in Table 2. The passivation range of Ti–15Moalloy (166–2513 mV vs. SCE) is relatively larger than Ti–6Al–4V alloy(155–1460 mV vs. SCE) and CP–Ti (145–1522 mV vs. SCE). The aver-age passive current density of all the three Ti materials lies is inthe range of 32 × 10−6 A/cm2. The surface morphology of CP–Ti,Ti–6Al–4V and Ti–15Mo alloys after subjecting them to polariza-tion studies indicate that their surface is free from pits. Alkhateeband Virtanen [29] have also reported that no signs of localized cor-rosion attack on the surface of CP–Ti (grade 2) after the polarizationstudies.

3.4.3. Cyclic polarization studiesThe cyclic polarization plots of CP–Ti, Ti–6Al–4V and Ti–15Mo

alloys in Ringer’s solution are given in Fig. 4. The reverse scan curveof all the three Ti materials came above the forward scan, which

indicates that, the Ti materials are resistant to pitting corrosion inRinger’s solution (Fig. 4(a) and (b) and Table 3). The pitting corrosionresistance of any material/coating, in general, can be ranked basedon the loop area of the cyclic polarization curves. The higher theloop area, the poorer is the resistance to pitting corrosion and vice

702 S. Kumar, T.S.N. Sankara Narayanan / Journal of Alloys and Compounds 479 (2009) 699–703

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ig. 4. Comparison of potentiodynamic polarization curves of the Ti alloys ininger’s solution (scan rate: 100 mV/min) (potentials in mV vs. SCE): (a) CP–Ti andi–15Mo alloy; and (b) Ti–15Mo and Ti–6Al–4V alloys.

ersa [30]. The loop area of all the three Ti materials studied is inhe range of (3.3–4.5) × 10−5 C/cm2 (Table 3). Among the three Ti

aterials, the loop area is relatively lower for Ti–15Mo alloy whenompared to CP–Ti (Fig. 4(a)) whereas the loop area of Ti–15Mond Ti–6Al–4V alloys is quite similar (Fig. 4(b)). This observationndicates that the pitting corrosion resistance of Ti–15Mo alloy isighly comparable to that of Ti–6Al–4V alloy but better than CP–Ti.liveira et al. [15] have also reported that no pitting corrosion hasccurred on Ti–Mo alloys in Ringer’s solution.

.4.4. Chronoamperometric/current–time transient studiesA chronoamperometric/current–time transient study, which is

measure of the change in current as a function of time at a con-tant impressed potential, would indicate the ability of Ti and itslloys to form a stable passive film. Chronoamperometric studiesave been used earlier by Alves et al. [17] and, Kumar and Sankara

able 3orrosion potential during the forward and reverse scans and the loop area of CP–Ti,i–6Al–4V and Ti–15Mo alloys in Ringer’s solution.

ype of Ti sample used E-1a (mV)vs. SCE

E-2a (mV)vs. SCE

Loop area(C/cm2)

P–Ti grade 2 −250 213 4.5 × 10−5

i–6Al–4V alloy −479 299 3.5 × 10−5

i–15Mo alloy −496 300 3.3 × 10−5

a E-1 and E-2: corrosion potential during the forward and reverse scans.

Fig. 5. Current–time transient curves of CP–Ti, Ti–6Al–4V and Ti–15Mo alloys inRinger’s solution at various anodic potentials: (a) 0.5 V; (b) 1.25 V; (c) 2 V; and (d)3 V (potentials in V vs. SCE).

Narayanan [18] to evaluate the passive state of Ti–Mo alloys insimulated oral environment at different anodic potentials. The CTTcurves of CP–Ti, Ti–6Al–4V and Ti–15Mo alloys in Ringer’s solutionat +0.5 and +1.25 V vs. SCE display similar characteristics; a rapiddecrease in current followed by a slow decay to attain a steady state.The observed behaviour could be explained based on the decreasein active area due to the growth of a passive film [17,18]. Thereis no appreciable variation in the steady state current density ofall the three Ti materials measured at +0.5 V vs. SCE (Fig. 5(a) andTable 4). However, a significant variation in the steady state currentdensity of all the three Ti materials is observed at +1.25 V vs. SCEand it follows the order: Ti–6Al–4V < CP–Ti < Ti–15Mo (Fig. 5(b) andTable 4). Unlike CP–Ti, the extent of dissolution and re-precipitation

nature of the film that would form on the surface of Ti–6Al–4V andTi–15Mo alloys. The relatively lower current density value observedfor Ti–6Al–4V alloy compared to CP–Ti and Ti–15Mo alloy at +1.25 Vvs. SCE is due to the formation of Al2O3 layer on its surface. The

Table 4Steady state current density of CP–Ti, Ti–6Al–4V and Ti–15Mo alloys in Ringer’ssolution measured at different impressed potentials.

Type of Ti sample used Steady state current density (1 × 10−6 A/cm2)measured at constant impressed potential

+0.5 V vs.SCE +1.25 V vs. SCE

CP–Ti grade 2 0.26 1.54Ti–6Al–4V alloy 0.32 0.99Ti–15Mo alloy 0.43 2.17

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elatively higher current density value observed for Ti–15Mo alloyndicates a possible dissolution of Mo from the alloy. However, allhe three Ti materials have the ability to quickly form a stable pas-ive film at +0.5 and +1.25 V vs. SCE. The results of the current–timeransient studies suggest that CP–Ti, Ti–6Al–4V and Ti–15Molloys possess better ability to form a stable passive film on theirurfaces.

The potentiodynamic polarization, cyclic polarization and CTTtudies of CP–Ti, Ti–6Al–4V and Ti–15Mo alloys in Ringer’s solu-ion reveal that the corrosion resistance of Ti–15Mo alloy is highlyomparable to that of Ti–6Al–4V alloy but better than that ofP–Ti. Though the hardness of Ti–15Mo alloy is lower than thatf Ti–6Al–4V alloy, being a �-phase alloy the Ti–15Mo alloys expected to offer better modulus property than CP–Ti andi–6Al–4V alloy [6,13]. Besides, the absence of toxic elements suchs V and Al render Ti–15Mo alloy much safer to be used in humanody. Hence, the Ti–15Mo alloy that possesses a �-phase struc-ure, moderate hardness and higher corrosion resistance could besuitable alternative material for orthopedic implant applications.

. Conclusions

The microstructure and structural characteristics confirm thati–15Mo alloy possess equiaxed �-phase in it is microstructure.he hardness of Ti–15Mo alloy (238HV0.2) lies between that ofP–Ti (175HV0.2) and Ti–6Al–4V alloy (324HV0.2). The OCP of CP–Tind Ti–6Al–4V alloy is almost the similar, −520 and −516 mV vs.CE, respectively, while the OCP of Ti–15Mo alloy is −477 mV vs.CE. Potentiodynamic polarization curves of CP–Ti, Ti–6Al–4V andi–15Mo alloys in Ringer’s solution are quite similar. The aver-ge passive current density of all the three Ti materials lies isn the range of 32 × 10−6 A/cm2. However, the passivation rangef Ti–15Mo alloy (166–2513 mV vs. SCE) is relatively larger thani–6Al–4V alloy (155–1460 mV vs. SCE) and CP–Ti (145–1522 mVs. SCE). The loop area of the cyclic polarization curve of Ti–15Molloy is quite similar to that of Ti–6Al–4V alloy but smaller than thatf CP–Ti. There is no appreciable variation in the steady state cur-ent density of all the three Ti materials measured at +0.5 V vs. SCEhile a significant variation is observed at +1.25 V vs. SCE. All the

hree Ti materials have the ability to quickly form a stable passivelm in Ringer’s solution at +0.5 and +1.25 V vs. SCE. The �-phasetructure, moderate hardness and the ability to offer a better cor-osion resistance in Ringer’s solution enables Ti–15Mo alloy as auitable alternative material for orthopedic implant applications.

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lloys and Compounds 479 (2009) 699–703 703

Acknowledgement

The authors express their sincere thanks to Prof. S.P. Mehro-tra, Director, National Metallurgical Laboratory, Jamshedpur, for hiskeen interest and permission to publish this paper.

References

[1] P. Kovacs, J.A. Davidson, in: S.A. Brown, J.E. Lemons (Eds.), Medical Applicationsof Titanium and Its Alloys: The Material and Biological Issues, ASTM STP 1272,ASTM International, West Conshohocken, PA, 1996, pp. 163–178.

[2] J.A. Hunt, M. Stoichet, Curr. Opin. Solid State Mater. Sci. 5 (2001) 161–162.[3] C. Fonseca, M.A. Barbosa, Corros. Sci. 43 (2001) 547–559.[4] M. Long, H.J. Rack, Biomaterials 19 (1998) 1621–1639.[5] S. Rao, T. Ushida, T. Tateishi, Y. Okazaki, S. Asao, Bio-Med. Mater. Eng. 6 (1996)

79–86.[6] W.F. Ho, C.P. Ju, H. Chern Lin, Biomaterials 20 (1999) 2115–2122.[7] R. Banerjee, S. Nag, J. Stechschulte, H.L. Fraser, Biomaterials 25 (2004)

3413–3419.[8] S. Nag, R. Banerjee, H.L. Fraser, J. Mater. Sci. Mater. Med. 16 (2005) 679–685.[9] L.D. Zardiackas, D.W. Mitchell, J.A. Disegi, in: S.A. Brown, J.E. Lemons (Eds.),

Medical Applications of Titanium and its Alloys: The Material and BiologicalIssues, ASTM International, West Conshohocken, PA, 1996, pp. 60–75.

10] K. Wang, Mater. Sci. Eng. A 213 (1996) 134–137.[11] D.M. Gordin, T. Gloriant, G. Texier, I. Thibon, D. Ansel, J.L. Duval, M.D. Nagel, J.

Mater. Sci. Mater. Med. 15 (2004) 885–891.12] C.M. Lee, W.F. Ho, C.P. Ju, J.H. Chern Lin, J. Mater. Sci. Mater. Med. 13 (2002)

695–700.13] S. Nag, R. Banerjee, H.L. Fraser, Mater. Sci. Eng. C 25 (2005) 357–362.14] W.F. Ho, J. Alloys Compd. 464 (2008) 580–583.15] N.T.C. Oliveira, G. Aleixo, R. Caram, A.C. Guastaldi, Mater. Sci. Eng. A 452–453

(2007) 727–731.16] J.E.G. González, J.C. Mirza-Rosca, J. Electroanal. Chem. 471 (1999) 109–115.

[17] A.P.R. Alves, F.A. Santana, L.A.A. Rosa, S.A. Cursino, E.N. Codaro, Mater. Sci. Eng.C 24 (2004) 693–696.

18] S. Kumar, T.S.N. Sankara Narayanan, J. Dent. 36 (2008) 500–507.19] N.T.C. Oliveira, A.C. Guastaldi, Corros. Sci. 50 (2008) 938–945.20] N.T.C. Oliveira, A.C. Guastaldi, Acta Biomater. 5 (2009) 399–405.21] M. Karthega, V. Raman, N. Rajendran, Acta Biomater. 3 (2007) 1019–1023.22] M.V. Capela, H.A. Acciari, J.M.V. Capela, T.M. Carvalho, M.C.S. Melin, J. Alloys

Compd. 465 (2008) 479–483.23] H.S. Dobbs, J.L.M. Robertson, in: H.A. Luckey, F. Kubli (Eds.), Titanium Alloys in

Surgical Implants, ASTM STP 796, ASTM International, West Conshohocken, PA,1983, pp. 227–240.

24] R.W. Schutz, D.E. Thomas, Corrosion, in: J.R. Davis (Ed.), in: Metals Handbook,vol. 13, 9th ed., ASM International, 1987, p. 671.

25] R. Davis, H.M. Flower, D.R.F. West, J. Mater. Sci. 14 (1979) 712–722.26] P.J. Bania, in: D. Eylon, R. Boyer, D. Koss (Eds.), Beta Titanium Alloys in the 1990s,

27] M. Ikeda, S.Y. Komatsu, I. Sowa, M. Niiomi, Metall. Mater. Trans. A 33 (2002)487–493.

28] Y. Okasaki, Mater. Trans. 43 (2002) 3134–3141.29] E. Alkhateeb, S. Virtanen, J. Biomed. Mater. Res. 75A (2005) 934–940.30] I. Gurrappa, Surf. Coat. Technol. 161 (2002) 70–72.