w.elsevier.com/locate/tsf

Thin Solid Films 515 (

Wear resistant and anti-corrosive treatment for TI–6AL–4V using

metal vapor vacuum arc source in comparison with plasma immersion

ion implantation

Chia-Wei Chang a, Jiunn-Der Liao a,b,*, Huan-Jen Chen b, Charlie S.F. Chang c, Song-Mao Chiu d

a Institute of Micro-Electro-Mechanical-System Engineering, National Cheng Kung University, 1, University Road, Tainan 701, Taiwan (ROC)b Department of Materials Science and Engineering, National Cheng Kung University, 1, University Road, Tainan 701, Taiwan (ROC)

c Duratek Incorp., 320, Sec. 1, Huandung Road, Science-Based Industrial Park, Tainan 600, Taiwan (ROC)d Metal Industries Research and Development Centre, 1001, Kao-Nan Road, Kaoshiung 811, Taiwan (ROC)

Available online 19 January 2006

Abstract

This study utilizes two ion-implantation methods, plasma immersion ion implantation (PIII) and metal vapor vacuum arc (MeVVA), to prepare

Ti–N phases on the surface of Ti–6Al–4V. By the nitrogen PIII method, both nitrogen and minor oxygen species are simultaneously attracted by

the negatively charged substrate. The penetration of N and O interstitial elements to an extensible depth is possible owing to the effect from the

negatively charged target. The nitrogen PIII treatment does not produce a novel Ti–N phase. As a result, the modified surface does not behave

anticorrosive. The Hn and the E determined by nanoindentation also remain unchanged. It is still potential to apply this non-directional treatment

by increasing bias voltage of the target, coating pure titanium on Ti–6Al–4V, and adjusting the regeneration process of nitrogen ions. The

MeVVA treatment creates a novel aTiN0.3 (011) phase on Ti–6Al–4V in present study. It signifies that the interactions between kinetic Ti ions of

varied energies and minor nitrogen molecules, with minor participation of oxygen, are highly feasible. The novel ion-implanted Ti–N phase is

corrosion resistant, which is capable to reduce passivation current density by forming a passive film. Moreover, the MeVVA-treated surface is

surface-hardened; the E is simultaneously increased. The increase of nano mechanical properties can be visualized by 3D images using Nano

Vision and determined by analyzing the tip/surface impact structure on the indentation site.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Plasma immersion ion implantation; Metal vapor vacuum arc; Anticorrosive; Nanoindentation; Nano Vision

1. Introduction

Ion implantation techniques are physical methods capable

to create a diffused layer of desired elements into a metal

surface that are dissimilar to coating techniques, which

usually alter the size and the dimension of a target substrate

[1–3]. The formation of a modified layer/substrate interface

with dimensional precision is an increasingly important factor

especially in modern micro or nano scale fabrication. Among

them, plasma immersion ion implantation (PIII) has been

developed to improve mechanical, chemical or physical

property of metal or polymer surfaces for more than a decade

0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.tsf.2005.12.047

* Corresponding author. Department of Materials Science and Engineering,

National Cheng Kung University, 1, University Road, Tainan 701, Taiwan

(ROC). Tel.: +886 6 2004232; fax: +886 6 2346290.

E-mail address: jdliao@mail.ncku.edu.tw (J.-D. Liao).

[1,4,5]. Low-pressure gaseous plasma is introduced as the

source of ionized elements for the implementation of PIII

technique, thereafter the substrate is exerted a constant and

negative impulse bias [6]. Plasma ions in the vicinity of the

target substrate are encompassed and bombard into the target

substrate, which may result in a layer of several hundreds

nanometer depth [1,7]. The major advantage of employing

ionized species in plasma is built upon a non-directional

treatment toward a target substrate, whereas the flux of ionized

particles is steadily discontinuous and an ion-poor sheath is

formed as a pulse bias acting on the substrate [4,8]. The

consequence of plasma-induced ions into a metal surface is

therefore correlated with the ionized density of plasma [9–12],

the frequency and potential of the applied impulse bias and

surface structure of the target substrate. It is convenient to

maintain the latter two parameters; as a result, the supply of

plasma ions mainly depends upon the quantity of ionized

2006) 122 – 128

ww

C.-W. Chang et al. / Thin Solid Films 515 (2006) 122–128 123

species in plasma sheath [8]. Previous study has indicated that

excited non-oxygen plasma, at the same time, contains minor

oxygen from the walls of flowing pathway or the reaction

chamber owing to the characteristic of using afterglow region

of plasma [12]. Such minor oxygen in radical or ionic forms

may play an important role to participate the reactivity of

plasma-induced treatment [11,12]. The composition of reactive

species in plasma is therefore influential in determining surface

properties of a thin PIII-treated layer.

In addition, the ionized source for PIII treatment usually

contains light gaseous elements such as argon, nitrogen,

oxygen, etc. To implant heavy metal ions into a substrate, it

is still feasible to deposit a thin metal film upon a target

substrate, followed by PIII treatment. Alternatively, a direct ion

implantation is applicable by taking accelerated ions or ions

from metal vapor vacuum arc (MeVVA) source [3,13,14]. The

former method is executed by extracting accelerated ions from

plasma source, which therefore produces ions-only beam

source to bombard a target substrate. The latter one is designed

to evaporate the exposure surface of a metal bar. The advantage

of using MeVVA source with ion acceleration is to extract the

evaporated metal ions, even ions from heavy metal, and to

strike into the target substrate, whereas the ions-only source is

directional and incapable to treat a surface with irregular

shapes. On the other hand, the chamber for acceleration-type or

MeVVA source ion implantation can be saturated with non-

excited gaseous molecules that probably collide with proces-

sing ions and simultaneously run into the target substrate that is

usually charged negatively. Such purged gaseous molecules in

non-excited form originally do not contain oxygen-derivative

species and is suitable for comparing with PIII treatment on

this particular oxygen-induced effect.

In this study, analogous surfaces are prepared with different

implantation doses and bias voltages in order for a comparison

of both techniques. Surface-sensitive measurements such as X-

ray photoelectron spectroscopy (XPS), Auger electron spec-

troscopy (AES), and glazing incidence X-ray diffraction

(GIXRD) are utilized for surface analyses and thereafter

nano-mechanical properties and corrosion resistance are

characterized and assessed.

2. Materials and method

2.1. Sample preparation and ion implantation

A commercially available Ti–6Al–4V was used and cut

into discs of 5 mm thickness, which were ground and polished.

The surface roughness (Ra) of the samples is �2.47 nm,

measured by scanning probe microscopy (SEIKO SPA300HV).

The PIII equipment was provided by Metal Industry

Research and Development Center (Kaohsiung, Taiwan). The

implantation parameters were: nitrogen plasma with RF or DC

magnetron, pulse bias of max 80 kV, pulse time of max 20 As,and pulse frequency of max 3000 Hz. The implantation doses

were 5�1016, 1017, 2�1017 ions/cm2, which were measured

by a microprobe device for monitoring ion beam. The glow

discharge RF plasma was produced using a 13.56 MHz plasma

generator with the max. power of 2 kW. An experimental value

of 800 W was applied with low energy reflection (<5%). The

operating parameters were: 99.9% nitrogen gas plasma of

26.7 Pa. Plasma density of the system was measured in the

range of 109 to 5�109 ions/cm3, using Langmuir probe and the

calculation method of thick-sheath theory [9–12].

The MeVVA system was provided by Duratek Incorp.

(Shinchu, Taiwan). The implantation parameters were: immer-

sion of 99.999% N2 atmosphere, pressure of 2.1�10�3 Pa,

pulse bias of 25 kV, and implantation doses of 5�1016, 1017,

2�1017 Ti-ions/cm2, respectively.

2.2. Water droplet contact angle measurement

Water contact angles were measured in two states: imme-

diately after removed from ion implanter and from desiccator

subsequent to several hours of placement. The measurements

were performed under argon atmosphere at 22T1 -C. The

sessile drop method was used and a JVC-TK1200 microscope

with processing software took the droplet image. For each

sample, ten measurements with a standard deviation below 1-were carried out and an average value was calculated. A water

droplet of �5 Al (scaled by HandyStep and Plastibrand,

BRAND, Germany) was used.

2.3. Surface analyses

The XPS was utilized for identifying the implanted

species. XPS spectra were acquired by a Physical Electronics

PHI 1600 spectrometer with a magnesium anode at 400 W and

15 kV–27 mA (Mg Ka 1253.6 eV, type 10–360 spherical

capacitor analyzer). To determine the elemental compositions

at the modified surface, the N 1s and Ti 2p core level spectra

were measured and calculated from XPS peak area with

correction algorithms and atomic sensitivity factors. The take-

off angle was fixed at 54.7-. The energy resolution was 0.7 eV,

while the energy scale was referenced to the pronounced Ti 2p

‘‘bulk’’ peak of 458.4 eV for Ti–6Al–4V sample and

calibrated for every sample. The spectra were fitted using

Voigt peak profiles and a Shirley background [9–12]. The AES

(VG-microlab 310D) was used for profiling the treatment

depth. The GIXRD (Hikaku Cu Ka, incidence angle of 1-) wasemployed for determining the crystalline structures on the

respectively modified surface.

2.4. Surface characterization

The nanohardness (Hn) and the Young’s modulus (E) of the

ion-implanted layer were measured by Nano Indenter XPimade by MTS System Corp. with the Continuous Stiffness

Measurements (CSM) and the Nano Vision for 3D image on

the indentation site. A triangular pyramid tip of Berkovich

diamond was used. The calculations of the Hn, the E, and the

function of the CSM were based on Oliver and Pharr [15]. The

loading process was controlled by a constant strain rate of 0.05.

The 3D color image to analyze the tip/surface impact on the

indentation site was taken soon after the indentation.

C.-W. Chang et al. / Thin Solid Films 515 (2006) 122–128124

Corrosion resistance of the pristine and the ion-implanted

surfaces were measured by an electrochemical instrument

(EG&G Instruments 263A) with potentiodynamic and poten-

tiostatic tests in 1 M H2SO4.

3. Results and discussion

3.1. The ion-implanted structure

The nitrogen PIII treatment did not produce Ti–N

structures on Ti–6Al–4V. As the negative impulse bias

reached to 20 kV and the implantation dose higher than

1017 particles/cm2, a low-intensity phase related to stacking

faults could be found. As a result, present PIII treatment

method was incapable to include a significant quantity of

N elements on the surface of the PIII-treated Ti–6Al–4V and

to form novel Ti–N crystalline structure, relevantly detected

by GIXRD. Since the supply of plasma ions mainly depends

upon the quantity of ionized species in plasma sheath, it is

likely that current bias voltage is still difficult to attract the

limited amount of nitrogen ions striking into the surface of

Ti–6Al–4V and thereafter to produce a significant quantity of

novel structure detectable by GIXRD.

On the other hand, the MeVVA treatment created aTiN0.3

(011) novel phase on Ti–6Al–4V (Fig. 1). It signifies that the

effect of kinetic Ti ions and relatively minor content of nitrogen

molecules, along with the ions, results in a significant quantity

of N elements in the Ti-ion implanted layer. Potentially a part

of low-energy Ti ions may collide with nitrogen molecules and

thereafter interact with nitrogen molecules, form the Ti,N-

containing species, and implant or solely deposit at the outmost

surface of Ti–6Al–4V. The results examined by GIXRD thus

provide that: (1) the MeVVA source is presently efficient, as

34 36 38 40 42 44 46

(b)2θ (de

αT

i 0,3 (0

11)

Tiα

(010

)

Tiα

(002

)

Tiα

(011

)

2 (deg.)

34 36 38 40

Tiα

(002

) α

Ti 0,

3 (011

)

Tiα

(010

)

(a)θ

Fig. 1. In the case of the MeVVA treatment with an implantation dose of 10

compared to the PIII method with current parameters, to

prepare a thin Ti–N layer; and (2) the interactions between

kinetic Ti ions of varied energies with minor nitrogen

molecules are highly feasible.

3.2. The N and O elements in the ion-implanted layer

Nitrogen plasma in the afterglow region, i.e. the reaction

chamber for the PIII treatment, contains a part of ionized

species and long-living radicals. In our previous measurements

[9–12], the reactive species in the region are dominated by

nitrogen ions and radicals, and minor content of oxygen ions

and radicals. The presence of oxygen species is naturally

resulted from the impurity of the gaseous molecules as well as

the contamination of the reactive chamber, which, even tested

in the ultra high vacuum system, can not be completely

avoided [12]. Accordingly, plasma immersion followed by the

extraction of energetic ions provides a particular kinetics

including physical and chemical effects to react with a target,

which is chemically different from the character of other

physical sources. The minor oxygen species in ionic or radical

states, in non-oxygen plasma are recognized as the highly

reactive species [11,12]. Non-oxygen plasma processing

involves several elementary reactions, which are supposedly

complicated and highly correlated with the presence of the O-

containing species.

The PIII treatment on a metallic target is non-directional.

Both nitrogen and minor oxygen species are simultaneously

attracted by the negatively charged substrate; at that time,

radical species may play a role to transfer energy with the

moving ions toward the substrate. Therefore, the nitrogen PIII

treatment is influenced by (1) an appropriate bias voltage

owing to the driving force to supply ionized species into the

(c)

Tiα

(011

)

2 (deg.)g.)

42 44 46 34 36 38 40 42 44 46

Tiα

(011

)

Tiα

(010

)

Tiα

(002

) α

Ti 0,

3 (0

11)

θ

17 Ti-ions/cm2 at 25 kV, novel aTi–N0.3 (011) phase was clearly found.

0 500 1000 1500 2000 2500 30000

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000

pristine 5 KV 10KV 20KV

Depth (1*10-10m)

20KV

10KV

5KV

pristine

Ato

mic

con

c. (

%)

, N

Sputtering time (sec)

(a)

0 500 1000 1500 2000 2500 30000

10

20

30

40

50

0 500 1000 1500 2000 2500 3000

pristine 5 KV 10KV 20KV

Depth (1*10-10m)

20KV10KV

5KV

pristine

Ato

mic

con

c. (

%)

, O

Sputtering time (sec)

(b)

Fig. 3. The depth profiling data for (a) N and (b) O elements on the surface of

the PIII-treated Ti–6Al–4V. At the bias voltage of 20 kV with an ion

implantation dose of 1017 ions/cm2, the penetrations of N and O elements were

obvious, while the extensions of N or O elements along with treatment depth

C.-W. Chang et al. / Thin Solid Films 515 (2006) 122–128 125

ion-poor region is highly correlated with the negatively

charged substrate; (2) a constant supply of energetic ions in

the vicinity of the negatively charged substrate; (3) the

unexpected presence of minor oxygen species, which exhibit

relatively low excitation energy, in comparison with that for

nitrogen species [11,12]; and (4) an appropriate regeneration

rate of ionized species to balance the neutralization of ions

containing different energies. Note that the highly energetic

electrons are usually absent in the reaction chamber.

For example, Fig. 2 illustrates the N 1s and Ti 2p XPS

spectra taken on the surface of the nitrogen PIII-treated Ti–

6Al–4V. The XPS data indicate that both Ti–N and Ti–O

structures are measured at the outermost surface. It is not only

an oxidation effect occurred at surface. Fig. 3a and b

furthermore exhibit the depth profiling data for N and O

elements inside the surface of Ti–6Al–4V using AES. The

AES measurements provide that, at the bias voltage of 20 kV,

the penetrations of N and O interstitial elements become

significant and extensible along with the treatment-effective

depth of several hundreds nm. The extension of N or O

elements in the Ti–6Al–4V matrix is likely correlated with the

negatively charged effect on the target substrate.

In the process of the MeVVA treatment, small portion of

nitrogen molecules was added along the pathway of the

evaporated Ti ions toward Ti–6Al–4V, which was relatively

minor with respect to the evaporated Ti ions. The effect of

kinetic Ti ions and relatively minor content of nitrogen

molecules, along with Ti ions, results in a slight quantity of

N elements in the Ti-ion implanted layer (Fig. 4). The

penetration depth of N interstitial elements is calculated

�500 nm, while that of O elements were largely reduced or

not measured. The MeVVA method is a directional treatment

that may significantly reduce the participation of oxygen

species to react with the vaporized Ti ions toward the target.

Note that the N 1s and Ti 2p XPS spectra for the MeVVA-

treated surface exhibit similar with those for the nitrogen PIII-

treated one.

410 405 400 395 390

Inte

nsity

(ar

b. u

nits

)

Binding Energy (eV)

TiNN 1s

pristine

50Kev

396.6 eV

470 465 460 455 450

TiN

pristine

Binding Energy (eV)

Ti 2p

456 eV

Ti2O

3

TiO2

Fig. 2. The N 1s and Ti 2p XPS spectra for the outermost surface of the

nitrogen PIII-treated Ti–6Al–4V. Both Ti–N and Ti–O structures were

present, which indicated the participation of O elements in the process. The

MeVVA-treated surface exhibited an analogous result (not shown).

were declined in different ways.

3.3. Chemical properties of the ion-implanted layer

As measured by XPS spectra, minor C,O-containing species

could be found on the PIII- or MeVVA-treated surface. For the

following tests, the adsorbed C,O-containing species were

mostly removed (i.e. identified by XPS).

Water droplet contact angle measurement is adequate to

interpret the wetting property representing for a part of the

complex structures at the ion-implanted surface. For examples,

for current case of the PIII treatment, water droplet contact

angles decreased from �42- to �24-, while for that of the

MeVVA treatment, the angles largely reduced from �42- to

�10-. Ion implantation on a metal surface tentatively results in

structural distortion that increases atomic packing in volume

density of parent planes. Therefore, the increase of surface

energy considerably reduces its contact angle with a water

droplet. The consequence is uncomplicated by introducing

0 1000 2000 3000 4000 5000 60000

10

20

30

40

50

60

70

80

90

1000 1000 2000 3000 4000 5000 6000

Ato

mic

con

c. (

%)

Sputtering time (sec)

C V N Al Ti

Depth (1*10-10m)

Fig. 4. The depth profiling data for N and other elements on the surface of the

MeVVA-treated Ti–6Al–4V. A slight quantity of N elements was found in the

Ti-ion implanted layer, whereas the penetration of N interstitial elements is

calculated �500 nm. The O elements were not measured.

0 5 10 15 200

2

4

6

8

10

12

Pas

siva

tion

curr

ent d

nsity

(A

/cm

2 ) *1

0-7

Ion implantation dose (ions/cm2) *1016

Fig. 6. As the measurement of passivation current density was fixed at 0.5 V vs.

SCE (presented in Fig. 5) with respect to implantation doses, the passivation

current density may be lowered to �5% for the implantation dose of 2�1017

Ti-ions/cm2 at 25 kV.

C.-W. Chang et al. / Thin Solid Films 515 (2006) 122–128126

imperfections of atomic arrangement in a solid material, which

noticeably provoke thermodynamic instability and increase

surface energy on the ion-implanted surface. Note that the

chemical structures at the outermost PIII- and MeVVA-treated

surfaces are analogous, as identified by XPS.

The MeVVA treatment provided novel Ti–N crystalline

structure on Ti–6Al–4V that significantly improved its

corrosion resistance, regardless of the applied implantation

doses (Fig. 5). Above all, as the implantation dose reached

1017 ions/cm2, an anticorrosive behavior by forming a passive

film was clearly observed. The measurement of passivation

current density (in A/cm2) at 0.5 V vs. SCE (saturated

calomel electrode) makes clear that the MeVVA-treated

surface is competent to reduce passivation current density

down to �5% for an ion implantation dose of 2�1017 ions/

cm2 (Fig. 6). On the other hand, present nitrogen PIII-treated

-9.0 -8.5 -8.0 -7.5 -7.0 -6.5 -6.0 -5.5 -5.0 -4.5 -4.0

-0.5

0.0

0.5

1.0

1.5

2.0

(b)

Pot

entia

l (V

vs

SC

E)

Log current density (A/cm2)

25KV pristine 5* 1016

1* 1017

2* 1017

(a)(d)

(c)

Fig. 5. Potentiodynamic curves for the MeVVA-treated Ti–6Al–4V with

different Ti-ion implantation doses. As the implantation dose reached to 1017

Ti-ions/cm2 at 25 kV, an anticorrosive behavior that formed a passive film was

clearly obtained.

surface was unlikely to perform an anticorrosive behavior (not

shown). It signifies that the modified surface using present

nitrogen PIII treatment does not exhibit corrosion-resistant,

whereas the presence of Ti–N phase on Ti–6Al–4V,

performed by the MeVVA method, is of great importance

to provide an anticorrosive property.

3.4. Mechanical properties of the ion-implanted layer

The Hn of the MeVVA-treated surface could be significantly

improved from �5 to �10 GPa by current parameters. The

increase was particularly obvious on the modified surface of

first 200 nm, but still effected to 500 nm (Fig. 7). The change

of the E was less important than that of Hn, whereas the E

might increase to �165 GPa at the outermost surface (not

shown) as compared to �150 GPa for the bulk. It signifies that

the increase of the Hn, in association with the applied load and

the indentation area on the indented site, is the consequence of

the presence of Ti–N phase. Note that the Hn is much

25kvcombine.xls Hardness vs Displacement Into Surface

0

2

4

6

8

10

12

14

0 500 1000 1500 2000 2500

Displacement Into Surface (nm)

Har

dn

ess

(GP

a)

25Kv11017.xls Hardness 25Kv2x1017.xls Hardness 25Kv5x1016.xls Hardness

Fig. 7. The Hn of the MeVVA-treated Ti–6Al–4V with different implantation

doses at 25 kV. The treatment significantly improved the Hn from �5 to �10

GPa for the ion implantation dose higher than 1017 Ti-ions/cm2, especially on

the surface of first 200 nm, but still effected to 500 nm.

C.-W. Chang et al. / Thin Solid Films 515 (2006) 122–128 127

correlated with the material response, plastic or elastic, in the

vicinity of the indented site. On the other hand, the increase of

E, in association with the unloading curve, is the consequence

of the increase of stiffness or the decrease of elastic

deformation during indentation. It is therefore clear that the

mechanical properties of the MeVVA-treated nano-layer are

much improved by the formation of Ti–N phase, whereas the

elastic property of the layer is simultaneously reduced.

Fig. 8a and b exhibit 3D tip/surface impact images using

Nano Vision on the indentation sites of the MeVVA-treated

surface. For the implantation dose of 1017 Ti-ions/cm2, the

strain deformation in the vicinity of the indentation site was

obvious (illustrated as a dark color in Fig. 8a), while a

Fig. 8. 3D images of the indentation sites using Nano Vision technique on the respec

the indentation by an ion implantation dose of 1017 Ti-ions/cm2, 2�1017 Ti-ion

deformation in the vicinity of the indentation was illustrated as a dark color shown in

site was shown in (b), (d) and (f). For an implantation dose of 2�1017 Ti-ions/cm2

shown in (d). The analogous measurements for the PIII-treated surface were compa

‘‘bulge’’ surrounding the indentation site could be clearly

found (Fig. 8b). The formation of the ‘‘bulge’’ is anticipated

to be a particular result from the discontinuity at the interface

between the ion-implanted layer and the surface of Ti–6Al–

4V. For a higher implantation dose such as 2�1017 Ti-ions/

cm2, the strain deformation area significantly hardened, which

tended to produce obvious creaks after an initial impact with

the indenter (Fig. 8c). The size and dimension of the ‘‘bulge’’

surrounding the indentation site became much apparent and

brittle (Fig. 8d) owing to the reduction of elastic property or

an increase of the E.

In contrast, the PIII-treated surface did not alter its

mechanical properties. The Hn and the E for the PIII-treated

tive surfaces: (a), (c) and (e), the top view and (b), (d) and (f), the side view of

s/cm2, and for the pristine surface of Ti–6Al–4V, respectively. The strain

(a), (c) and (e). The formation of a bulge-like part surrounding the indentation

, the strain-deformed area significantly hardened and produced obvious creaks

rable with those for the pristine surface of Ti–6Al–4V.

C.-W. Chang et al. / Thin Solid Films 515 (2006) 122–128128

surface were even inferior to those for the pristine Ti–6Al–4V

(not shown). It is a characteristic behavior to decrease both

values at the first hundred nanometers when the tested surface

is just sputtered and roughened. For a roughened surface, the

applied load tends to be reduced at the initial displacement of

the indenter. Consequently, the measured Hn is decreased. A

similar calculation can be made for the E. In this study, the

roughness of the nitrogen PIII-treated surface increased from

�2.47 to �8.56 nm, whereas that of the MeVVA-treated

surface is insignificantly altered.

A relatively slight strain deformation was found in the

vicinity of the indentation on the pristine surface of Ti–6Al–

4V (Fig. 8e). The indentation induced swelling part caused by

the tip/surface impact exhibited much continuous with the

indentation site (Fig. 8f), which was dissimilar with the

MeVVA-treated surface. The analogous measurements for the

PIII-treated surface were comparable with those for the pristine

surface of Ti–6Al–4V (not shown). Overall, the PIII treatment

on Ti–6Al–4V using the present parameters does not improve

the nano-mechanical properties on the surface of Ti–6Al–4V,

which corresponds well with the assessment of anticorrosive

behavior.

4. Conclusion

The nitrogen PIII treatment on the surface of Ti–6Al–4V is

non-directional. Both nitrogen and minor oxygen species are

simultaneously attracted by the negatively charged substrate.

The treatment does not produce Ti–N structures on Ti–6Al–

4V, whereas, at the bias voltage of 20 kV, the penetrations of N

and O interstitial elements become significant and extensible

along with the treatment-effective depth of several hundreds

nm. However, present nitrogen PIII-treated surface is unlikely

to have an anticorrosive behavior. The Hn and the E remain

unchanged.

The MeVVA treatment created a novel aTiN0.3 (011) phase

on Ti–6Al–4V. The effect of kinetic Ti ions and relatively

minor content of nitrogen molecules, along with the ions, results

in a significant quantity of N elements in the Ti-ion implanted

layer. The interactions between kinetic Ti ions of varied

energies and minor nitrogen molecules are highly feasible.

The MeVVA method is a directional treatment that may

significantly reduce the unexpected participation of O species

to react with the vaporized Ti ions toward the target. The

MeVVA treatment provides novel Ti–N crystalline structure on

Ti–6Al–4V that significantly improves its corrosion resistance

by forming a passive film and reducing the passivation current

density. The Hn and E of the MeVVA-treated surface

significantly increase at first the 200 nm, but still effected to

500 nm. With the increase of Hn, the elastic property of the

hardened layer declines which can be well distinguished by the

3D image on the indentation site.

Acknowledgement

This work was supported by National Science Council of

Taiwan under contract number NSC 93-2622-E-006-038-CC3

and projects, No. 92C17, 93C14 and 94-Explore, granted by

Metal Industry R&D Centre. The authors would also like to

appreciate the assistance from Metal Industries Research and

Development Centre and Duratek Inc. for providing the PIII

and the MeVVA equipment, respectively.

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