ho-gun kim, seung-ho ahn, jung-gu kim, *se-jun park, *kwang-ryol lee, **rizhi wang

Ho-Gun Kim, Seung-Ho Ahn, Jung-Gu Kim, *Se-Jun Park, *Kwang-Ryol Lee, **Rizhi Wang

SungKyunKwan University, Korea *Korea Institute of Science and Technology, Korea

** The University of British Columbia, Canada

Corrosion Resistance of Diamond-Like Carbon (DLC) Coatings on 316L Stainless Steel for

Biomedical Applications

Conference of Metallurgists COM2003, August 24-27, CanadaConference of Metallurgists COM2003, August 24-27, Canada

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

● Diamond-Like Carbon (DLC)? - amorphous structure similar to diamond - hydrogenated amorphous carbon( a-C:H )

INTRODUCTION

ADVANTAGES

●High hardness, low friction●Electrical insulation

WEAK POINT

●High compressive stress → buckling●Poor adhesion

Diamond-Like Carbon (DLC)’ A&W?

The purpose of the present investigation is to evaluate the effects of bias voltage and Si incorporation on the corrosion resistance of DLC coatings in the simulated body fluid environment.

●Chemical inertness●Resistance to wear

●Operation temperature below 500oC

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

DEPOSITION CONDITIONS

­­­RF­PACVD­(13.56­MHz)­RF­PACVD­(13.56­MHz)

­­­Base­Pressure­:­below­2.0×10­Base­Pressure­:­below­2.0×10-5-5­Torr­Torr

­­­­Silicon­Buffer­layer­(for­residual­stress)Silicon­Buffer­layer­(for­residual­stress)

­­­SiH­SiH44,­10­mTorr,­-400­V,­1­min.­deposition,­10­mTorr,­-400­V,­1­min.­deposition

­­­­DLC­Precursor­Gas­:­CDLC­Precursor­Gas­:­C66HH66

­­­Deposition­Pressure­:­1.33­Pa­Deposition­Pressure­:­1.33­Pa

­­­­Bias­Voltage­:­-­400­VBias­Voltage­:­-­400­V­­

­­­­Film­Thickness­:­­Film­Thickness­:­­1 1 ㎛㎛­­­­­­­­­­­­

Schematics of RF PACVDSchematics of RF PACVD

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

Si-C:H Bias Voltage = -400V Si-C:H Bias Voltage = -400V

EXPERIMENTAL PROCEDURES

Coating structureCoating structure

Substrate

C6H6

Buffer layer Si

Coating

5-7 nm

Substrate

Coating

Buffer layer

a-C:H Bias Voltage = -800Va-C:H Bias Voltage = -800V

a-C:H Bias Voltage = -400Va-C:H Bias Voltage = -400V

Substrate

C6H6+ SiH4

Buffer layer Si

Coating 1 ㎛

5-7 nm

1 ㎛

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

EXPERIMENTAL PROCEDURES

Electrochemical evaluationElectrochemical evaluation

Diamond-like carbon (DLC) coatingsDiamond-like carbon (DLC) coatings

Potentiodynamic polarization testPotentiodynamic polarization test

Electrochemical impedance Electrochemical impedance spectroscopy (EIS)spectroscopy (EIS)

Potential : -0.25 Voc~1.5 VScan rate : 0.166 mV/sec

Frequency : 10 mHz~10k HzAmplitude : 10 mV

Electrolyte : Deaerated 0.89% NaCl, 37℃,­pH=7.4 (similar to human body environment)

SEMSEM Surface and corrosion features

AFMAFM Uniformity of surface

Surface analysesSurface analyses

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

RESULTS AND DISCUSSION

SpecimenEcorr

(mV)

icorr

(nA/ ㎠ )

βa

(V/decade)

βc

(V/decade)

Rp

(×103 Ω ㎠ )Porosity

Substrate-

114.6249.3 0.1285 0.1868 132.7 -

Si-C:H,­Bias­voltage­=­-400V­-

111.60.06486 0.3527 0.06077 347492.9 0.00037

a-C:H, Bias voltage = -800V

-63.11

15.33 0.1211 0.1839 2070.8 0.02407

a-C:H, Bias voltage = - 400V

-40.55

103 0.5402 0.1293 440.3 0.15556

Porosity equation ( Matthews et al.)

F : Total porosity Rpm : Polarization resistance of the substrate △Ecorr : Difference of corrosion potential

between coated and uncoated specimens. Rp : Polarization resistance of the coated steels β a : Anodic Tafel slope of the substrate

Potentiodynamic polarization test

10-14 10-13 10-12 10-11 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

Pot

entia

l (m

V v

s S

CE

)

Current Density (A/cm2)

Substrate Si-C:H, Bias voltage = -400V a-C:H, Bias voltage = -800V a-C:H, Bias voltage = -400V

ΔEcorr/βa

substrate)-p(coating

e)pm(substat10

R

R F

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

RE : Reference electrode

WE

Rpore

CPE1CPE2Rct

Rs

RE

RESULTS AND DISCUSSION

Electrical equivalent circuit for coated metalElectrical equivalent circuit for coated metal

WE : Working electrode

Rs­:­Solution­resistance­between­working­electrode­­­­­­­and­reference­electrodeCPE1­:­Capacitance­of­the­coating­including­pores­­­­­­­­­­­­­in­the­outerlayer­coating­Rpore­:­Pore­resistance­resulting­from­the­formation­­­­­­­­­­­­of­ionic­conduction­paths­across­the­coatingCPE2­:­Capacitance­of­the­coating­within­the­pit­Rct­:­Charge­transfer­resistance­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­of­the­substrate/coating­­

Electrochemical parametersElectrochemical parameters

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

● Electrochemical parameters obtained by equivalent simulation

Exposuretime

Rs

(Ω ㎠ )

CPE1Rpore

(×103

Ω ㎠ )

CPE2Rct

(×103

Ω ㎠ )AdCcoat,

(×10-9

F/ ㎠ )

n(0-1)

Cdl

(×10-9

F/ ㎠ )

n(0-1)

120 h

Substrate 32.96 46440 1 78.9 175200 1 252.2 -

Si-C:H,­(-400V)

700.7 20.8 0.9921 3.43 47.47 0.7483 2501 0.41

a-C:H, (-800V)

11.39 5.2 0.8675 81.8 508.5 0.914 1018 1.08

a-C:H, (-400V)

929.1 878.4 0.6016 92.4 714.2 1 372.5 1.70

216 h

Substrate 33.29 48210 1 73.4 174200 1 218.2 -

Si-C:H,­(-400V)

4.308 27.1 0.9602 2.9 47.05 0.5329 2062 0.48

a-C:H, (-800V)

18.2 7.74 0.8884 52.5 749.4 0.8843 1292 1.69

a-C:H, (-400V)

696 899.4 0.6099 89.9 542.2 1 342 1.73

RESULTS AND DISCUSSION

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

RESULTS AND DISCUSSION

Si-C:H(-400V) coating leads to the higher Rct values than a-C:H(-400V).

a-C:H(-800V)­coating leads to the higher Rct­values than­a-C:H(-400V).

Charge transfer resistance (RCharge transfer resistance (Rctct))

1 24 48 72 96 120 144 168 192 216

0

2000

4000

6000

Ch

arg

e T

ran

sfe

r R

esi

sta

nce

(ko

hm

-cm

2 )

Immersion Time(h)

Substrate Si-C:H, Bias voltage = -400V a-C:H, Bias voltage = -800V a-C:H, Bias voltage = -400V

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

RESULTS AND DISCUSSION

RRpo po = R = Roopopo /A /Add ( R ( Rpopo= pore resistance )= pore resistance )

RRoopopo = ρd (ρ = specific resistance, d= coating thickness) = ρd (ρ = specific resistance, d= coating thickness)

Delamination area (ADelamination area (Add))

1 24 48 72 96 120 144 168 192 216-1

0

1

2

8

10

De

lam

ina

tion

Are

a(A

d)

Immersion Time(h)

a-SiC:H, Bias voltage = -400V a-C:H, Bias voltage = -800V a-C:H, Bias voltage = -400V

Si-C:H(-400V) coating leads to the lower delamination area than a-C:H(-400V).a-C:H(-800V) coating generally leads to the lower delamination area than

a-C:H(-400V).

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

RESULTS AND DISCUSSION

Deposited surfaces ( AFM )Deposited surfaces ( AFM )a-C:H(-400V)

Si-C:H(-400V)a-C:H(-800V)

RRaa = 0.2326 = 0.2326 ㎛㎛

RRaa = 0.6157 = 0.6157 ㎛㎛

RRaa = 0.0906 = 0.0906 ㎛㎛

Roughness of Si-C:H(-400V) was lower than a-C:H(-400V) according to Si incorporation. With increasing bias voltage, roughness of a-C:H(-800V) was lower than a-C:H(-400V).

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

RESULTS AND DISCUSSION

Corroded surfaces (After potentiodynamic polarization test)Corroded surfaces (After potentiodynamic polarization test)

Substrate Si-C:H(-400V)

a-C:H(-800V) a-C:H(-400V)

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

CONCLUSIONS

● From the potentiodynamic test, the polarization resistance value of Si-C:H(-400V) was higher than a-C:H(-400V). Also, the polarization resistance value of a-C:H(-800V) was higher than a-C:H(-400V).

● From the potentiodynamic test, porosity of Si-C:H(-400V) was lower than a-C:H(-400V). Moreover, porosity of a-C:H(-800V) was lower than a-C:H(-400V).

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

● From the EIS results, Rct value of Si-C:H(-400V) was higher than a-C:H(-400V). Furthermore, Rct­value of a-C:H(-800V) was higher than a-C:H(-400V).

●­From the EIS results, delamination area of Si-C:H(-400V) was lower than a-C:H(-400V). In addition,­delamination area of a-C:H(-800V) was lower than a-C:H(-400V).­These results corresponded with the potentiodynamic test.­

CONCLUSIONS

● It was shown that corrosion resistance of DLC films with Si incorporation and higher bias voltage would be improved in corrosive environment.

Applied Electrochemistry Lab. SKKUApplied Electrochemistry Lab. SKKU

● From the AFM images, the increase of bias voltage and Si incorporation improved the surface roughness of DLC coatings. These results are consistent with the porosity calculated by electrochemical method.