ISSN 2070-2051, Protection of Metals and Physical Chemistry of Surfaces, 2016, Vol. 52, No. 6, pp. 1079–1085. © Pleiades Publishing, Ltd., 2016.
PHYSICOCHEMICAL PROBLEMS OF MATERIALS PROTECTION
Corrosion Behaviour of Single and Double Layer Hydroxyapatite Coatings on 316L Stainless Steel by Plasma Spray1 Yusuf Kayalia, *, Osman Aslana, Muhammet Karabaşb, and Şükrü Talaşa aAfyon
Kocatepe University, Faculty of Technology, Department of Metallurgical and Materials Engineering, Turkey bİstanbul Technical University, Faculty of Metallurgy-Chemistry, Department of Metallurgical and Materials Engineering, Turkey *e-mail:
[email protected],
[email protected] Received January 21, 2016
Abstract—AISI316L stainless steel is extensively used in orthopedic and dental applications. However, this alloy exhibits low integration behaviour when it comes in contact with surrounding bone tissue and implant healing duration can be as much as few months. The aim of this study is the fabrication of biocompatible hydroxyapatite (HA) coatings on stainless steel substrate in order to accelerate the process of osseointegration of implants. The biocompatible single layer of Titania (TiO2), Hydroxyapatite and bi-layer TiO2/HA coatings were deposited by atmospheric plasma spray on 316L stainless steel. Coated and uncoated stainless steel specimens were incubated in simulated body fluids and 0.9% NaCl solutions for 1h and 7 days. In vitro electrochemical-corrosion evaluation of coated and uncoated stainless steel specimens have been investigated by Tafel extrapolation and linear polarization methods. Results indicates that corrosion resistance of single layer HA coated stainless steel specimens are superior to single layer TiO2 and bi-layer HA/TiO2 coated stainless steel specimens. DOI: 10.1134/S2070205116060113
1. INTRODUCTION AISI 316 L austenitic stainless steel, due to its high corrosion resistance at high temperatures, has a wide range of industrial applications such as petro-chemical industry, paper industry and in nuclear engineering etc. They are also used in the medical field as implant materials because of their biocompatibility, low cost, good mechanical properties, fabrication simplicity, and corrosion resistance [1–3]. These steels have a low carbon content approximately 0.030–0.025 wt %. Carbon forms carbides at the grain boundaries, which reduce the corrosion resistance of the grain boundary [1]. Studies carried out to date have shown that about 70% of damage in the medical implants made by 316L SS are due to corrosion [4, 5]. But, some studies indicated that different damage machanism such as erosion-corrosion, corrosion fatigue, fretting fatigue, and wear accelerated by corrosion [6–11]. Corrosion of materials in body fluids can cause of toxicity and allergic reactions due to release of metal ions in the human body [13]. The stability of the surface oxide layer is one of the most important requirements of a medical implant materials [14]. In 316L SS, the stability of the surface oxide layer is not very high and the possibility of metal ions being released is greater in comparison to other implant materials [2]. 1 The article is published in the original.
Therefore, in recent years, with development of technology and the expectation of superior properties from materials, surface modification of 316L stainless steel implant materials has been the subject of many studies. The application of hydroxyapatite or other biocompatible materials on metallic implants as a bioactive coating was used in order to improve biocompatibility because of chemical composition close to that of bone tissue [15, 16]. HA coatings on implants materials provoke development of bone cells between the human tissues and implant materials and lead to rapid biological fixation of implants to bone tissue [17–19]. Commonly used HA coating techniques are sol-gel [20], ion implantation [21], chemical vapor deposition [22], laser deposition [23], sputtering [24], and thermal spraying techniques such as plasma spraying, flame spraying, high-velocity oxy-fuel (HVOF) [25]. Plasma spray process is the most commonly used technique for fabrication of biocompatible HA coating. Previous works indicate that the using of bond coats between top HA coating and metalic implant materials improve the surface properties and adhesion strenght of HA coating [26]. Titania (TiO2), zirconia (ZrO2), alumina (Al2O3), and titanium (Ti) are used as bond coat or particle composite coats with HA in different ratios to improve the mechanical and biological properties of HA coatings [27–29]. TiO2 coating has
1079
1080
YUSUF KAYALI et al.
Table 1. The chemical composition of test materials (wt %) Steel AISI 316 L
C
Cr
Ni
Si
Mn
Mo
Cu
N
P
S
Ti
0.020
16.889
10.616
0.386
1.501
2.111
0.344
0.054
0.033
0.030
0.008
Table 2. Spray parameters of the plasma spray coating process Parameters Plasma Current (I, amp) Ar plasma gas flow (scfh) H2 plasma gas flow (scfh)
500 90 15
Ar powder feeding gas flow (scfh) Number of passes Spray distance (mm) Speed of spray gun (mm/min) Speed of specimen table (rpm)
13.5 12 75 200 100
cps/eV 10
(a)
Ca
8
8 µm
P
6 P
Ca
4 O 2 Ca Ca
0
2
4
6
cps/eV 16
8
10
keV
(b)
14 Ti
12
100 µm
10 Ti
8 6 4 Ti 2 0
O
Ti
2
4
6
8
10
12
keV
Fig. 1. Plasma Spray coating powders (a) hydroxyapatite powder (b) TiO2 powder morphology.
attracted much attention as a composite or bond coat material because of its biological and corrosion resistance effects [30]. In the present study; the corrosion properties of AISI 316 L austenitic stainless steel specimens which are in the form of uncoated, coated with biocompatible single-layer HA, TiO2 and double-layer HA + TiO2 coatings by plasma spray coating method were determined by the microstructure and electrochemical analysis in different media 0.9% NaCl and SBF (Simulated Body Fluid). Corrosion properties of the coated and uncoated AISI 316L austenitic stainless steel were compared with each other. 2. EXPERIMENTAL STUDY The chemical composition of AISI 316 L stainless steel used in the study are given in Table 1. In this study, ∅15 × 10 mm and M5 threaded AISI 316 L stainless steel materials, have been selected as base. Before the coating process, the surface of base material was cleaned and roughened by sandblasting. Commercially produced Sulzer Metco TiO2 and spray dried HA powders were used for the spray coating process with Sulzer Metco 9MB plasma gun attached with 730C nozzle. The plasma gun was mounted on a CNC robot which allows the desired speed and movement. The sanded specimens placed onto a revolving turntable and powders were sprayed perpendicularly to the sample to achieve a uniform coating thickness distribution. Table 2 shows the process parameters used during the coating process. With the process parameters given above, 100% HA, 100% TiO2 and 50% TiO2 + 50% HA containing coating powders are applied onto the sand blasted samples. Morphologies of the powder coatings used in the experimental study were compared with the SEM-EDX analysis (Fig. 1). As seen from Fig. 1, the morphology of the HA powder are spherical and particle size distribution is similar to each other. The TiO2 particles have the morphology of more angular and pointed. The phase compositions of TiO2, HA feedstock powders and the assprayed coatings were analyzed using an XRD instrument with CuKα radiation (Fig. 2). As can be seen in Fig. 2, HA and TiO2 powders consist of crystalline phases. Before starting the electrochemical experiment, the surfaces of specimens were respectively cleaned in acetone, ethyl alcohol and double distilled water for 15 min in Bandelin brand ultrasonic bath at 30°C, and followed by the drying at 40°C for 1 h in an incubator.
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES
Vol. 52
No. 6
2016
CORROSION BEHAVIOUR OF SINGLE AND DOUBLE LAYER
600
(a)
TiO2
cps/eV 14
400
12
300
10
200
8
100
6
0 20 30 40 50 60 70 80 90 300 (b) HA 280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 20 30 40 50 60 70 80 90 2Theta (Coupled Two Theta/Theta) WL = 1.54060
4
Counts
500
1081
(a) Ca 20 µm P
Counts
HA
MATRİS
O Ca
2 Ca 0
2
4
6 (b)
cps/eV
3. RESULT AND DISCUSSION 3.1. Characterization of Coatings SEM-EDX pictures were taken from the surface of the coated AISI 316 L stainless steel specimens (Fig. 3). After Plasma spray process, the powders were shown to attach to the substrate. EDX analysis from coated AISI 316 L stainless steel surface proved the formation of the surface coating. The coating thickness in HA + TiO2 coated specimens was 150 μm in average, TiO2 peaks were not detected as a result of blocking effect of HA. As seen in Figure 3a that the main elements of HA i.e. Ca, P and O were strongly detected on the surface. Similar results were also obtained in the literature [31, 32]. Figure 4a and 4b show XRD patterns of HA and HA + TiO2 bi-layer coated samples. The analysis shows that all the major peaks belong to HA, tetracalcium phosphate ((Ca4(PO4)2O)–TTCP), β-tricalcium phosphate (β-Ca3(PO4)2)–β-TCP) and
10
12 keV
Ti
12
20 µm
10 8
TiO2
6 MATRİS
4 Ti
2Ti 0
For corrosion experiments, Gamry reference 600 potentiostat/galvanostat and Echemanalyst softwares were employed to collect data from specimens. Uncoated and coated AISI 316L specimens were held in SBF and 0.9% NaCl solution for 1 and 168 h at the temperature of 37°C and current potential diagrams were obtained at the end of corrosion tests.
8
14
O
Fig. 2. XRD patterns of feedstock powders.
100 µm
2
4
cps/eV
100 µm
6 (c)
8
10
12 keV
12 Ca
10
20 µm
8 P
6
HA TiO2 MATRİS
4 2
O
Ca
100 µm
Ca
0
2
4
6
8
10
12 keV
Fig. 3. SEM-EDX images of (a) HA, (b) TiO2, (c) HA + TiO2 coated AISI 316L stainless steel.
CaO phases. Figure 4c shows XRD patterns of single layer TiO2 coated sample. The XRD pattern of TiO2 coating shows that all the major peaks belong to TiO2 rutile phase. The XRD patterns of coatings indicate that there is no observed phase transformation for the HA and TiO2 powders during plasma spray process.
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES
Vol. 52
No. 6
2016
1082
YUSUF KAYALI et al.
(a) Tafel scan
(a)
Counts
300 200 100
400 Vf, mV vs. ref.
558-HA + TiO2.brml PDF 00-011-0232 Ca4 P2O5 Calcium Phosphate PDF 01-074-9761 Ca4.776 (H0.39 (PO4)3)(OH)0.942 Hydroxyapalite PDF 01-070-4068 Ca O Calcium Oxide PDF 00-001-1393 TiO2 Rutile PDF 01-070-0364 Ca3 (PO4)2 Calcium Phosphate
200
AISI 316 L SS HA coated HA + TiO2 coated TiO2 coated
0 –200 –400
0 20
30
40
50
60
70
80
90
–600 10 nA 100 nA
(b) PDF 00-032-0178 Ca3 (PO4)2 Tuba. syn PDF 00-011-0232 Ca4 P2O5 Calcium Phosphate PDF 01-070-0364 Ca3 (PO4)2 Calcium Phosphate PDF 01-070-4068 Ca O Calcium Oxide PDF 01-074-9761 Ca4.776 (H0.39 (PO4)3)(OH)0.942 Hydroxyapalite
400
600 500
Vf, mV vs. ref.
Counts
280 260 240 220 200 180 160 140 120 100 80 60 40 20 0 20
30
40
50
60
70
80
200
1 uA 10 uA 100 uA 1000 uA Im, A (b) Tafel scan
AISI 316 L SS HA coated TiO2 coated HA + TiO2 coated
0 –200
90
(c) 557-TiO2.brml PDF 01-070-7347 TiO2 Rutile PDF 01-080-0787 Ca (SO4) Calcium Sulfate
Counts
400
–400 –600 10 nA 100 nA
1 uA 10 uA 100 uA 1000 uA Im, A
300 Fig. 5. The Tafel curves obtained in 0.9% NaCl solution for (a) 1 h, (b) 168 h holding times.
200 100 0 20 30 40 50 60 70 80 90 2Theta (Coupled Two Theta/Theta) WL = 1.54060 Fig. 4. XRD patterns of plasma sprayed coatings, (a) HA + TiO2, (b) HA, (c) TiO2.
3.2. Corrosion Behaviour The linear polarization and Tafel results obtained from 0.9% NaCl solution as a result of holding for 1 h and 168 h, are given in Table 3 and Fig. 3. When Table 3 is examined, it can be seen that icorr values decreased after 1 h holding in 0.9% NaCl. However, with the increase in the holding time, polarization current density (icorr) values also increased. The poor corrosion resistance was obtained in the samples coated with TiO2 as a result of holding in 0.9% NaCl solution. 0.9% NaCl medium, with the holding time of 1 h, icorr values produced more positive potential. This, in turn, resulted in more lineage potential for the surface of the specimens because of HA coating and therefore led to
higher corrosion resistance [33–35]. In addition, the values of polarization resistance, Rp and corrosion rate (mpy) appears to be in agreement with icorr values (Fig. 5). Linear polarization Tafel results were obtained as a result of holding for 1 and 168 h in SBF solution and are given in Table 4 and Fig. 6. When Table 4 is examined, icorr values of coated sample increased along with the increase in holding time in the SBF media while a decrease in the corrosion resistance of TiO2 and HAP + TiO2 coated AISI 316 L stainless steel were observed. Polarization current density (icorr) values in uncoated condition varies between 0.301 and 0.331 μA/cm2, however, polarization current density values of the coated specimens, depending on the type of coating, were observed to be between 0.176 and 3.873 μA/cm2. The HA layer is said to prevent the corrosion at low holding times. The results are in accordance with the literature [36–38]. In Figs. 7, 8, EDX analysis from the surfaces showing the best and the worst corrosion resistance
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES
Vol. 52
No. 6
2016
CORROSION BEHAVIOUR OF SINGLE AND DOUBLE LAYER
1083
Table 3. Corrosion results obtained in 0.9% NaCl medium Ecorr, mV
icorr, μA/cm2
Uncoated HA coated TiO2 coated
269 308 257
1 hour 0.443 0.125 1.376
50.62 80.46 27.95
0.199 0.197 0.619
HA + TiO2 coated
223
1.274
31.65
0.574
Uncoated HA coated TiO2 coated
255 238 320
155.1 42.90 6.497
0.090 0.533 2.547
HA + TiO2 coated
269
17.01
0.658
37°C in % 0.9 NaCl
Rp, kΩ
168 hours 0.202 1.183 5.657 1.461
are given to determine the changes in surface composition. The best corrosion resistance, as seen from the EDX analysis in Figs. 7, 8, was obtained in the HA-coated specimens for the reason that a protective oxide layer is formed on the surface of HA cotaed specimens [36–38].
Corrosion rate, mpy
cps/eV
(a)
16 14 12
Ca
100 µm
10 (a) Tafel scan
Vf, mV vs. ref.
400 200
O: 45.65 Ca: 40.76 P: 13.60
8 P
AISI 316 L SS HA coated HA + TiO2 coated TiO2 coated
6 4
0
2
O
0
–200
Ca
Ca
2
4
cps/eV
–400
100 nA
Vf, mV vs. ref.
400
1 uA Im, A (b) Tafel scan
10 uA
100 uA
200
8
10 keV
(b)
16 –600 10 nA
6
Ti
14 12
100 µm
10 O: 40.28 Ti: 59.72
8 6
0
4 O
–200 –400 –600 10 nA 100 nA
Ti
2 Ti 0
2
4
6
8
10 keV
1 µA 10 uA 100 uA 1000 uA Im, A
Fig. 6. The Tafel curves obtained in SBF solution for (a) 1 h, (b) 168 h holding times.
Fig. 7. EDX analysis of surfaces after corrosion tests in 0.9% NaCl solution (a) 1 h HA coated, (b) 168 h TiO2 coated specimens.
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES
Vol. 52
No. 6
2016
1084
YUSUF KAYALI et al.
Table 4. Corrosion characteristics obtained in SBF medium icorr, μA/cm2
Ecorr, mV
37°C in SBF
Rp, kΩ
Corrosion rate, mpy
1 hour Uncoated
254
0.301
34.60
0.207
HA coated
215
0.176
52.48
0.136
TiO2 coated
293
0.849
11.10
0.382
HA + TiO2 coated
260
0.617
14.07
0.277
168 hours Uncoated
301
0.331
64.24
0.149
HA coated
278
0.404
45.33
0.182
TiO2 coated
440
3.873
4.043
1.743
HA + TiO2 coated
390
2.837
6.033
1.276
cps/eV
(a)
12 Ca
10
100 µm
8
O: 43.62 Ca: 40.68 P: 14.05 Si: 1.65
P
6 4 2 O Ca
0
Si
2
Ca
4
6 (b)
cps/eV
8
10 keV
16 14
Ti
12
100 µm
10
O: 37.90 Ti: 62.10
8 6 4
ACKNOWLEDGMENT This work has been supported by Scientific and Research Project Commission (Project no. 13.FEN.BİL.54). REFERENCES
Ti 2 O
0
4. CONCLUSIONS Following results were obtained from single-layer and double layer coatings on the surface of AISI 316L stainless steel with a plasma spray coating method using HA and TiO2 powders: • SEM-EDX analysis after the plasma spray coating showed that HA, HA + TiO2 and TiO2 coatings were well attached to the surface and a uniform coating thickness for all coatings were achieved throughout the specimen surface. • The corrosion resistance of 316L stainless steel with HA coating in 0.9% NaCl solution improved about 60% in 1 hour holding time and approximately 50% in the SBF solution. • In all coatings, with increasing holding time in the solution resulted in a decrease in corrosion resistance and increase in current densities. • The weakest corrosion resistance in both 0.9% NaCl and the SBF solution for the holding times of 1 h and 168 h were obtained in TiO2 coated specimens.
Ti
2
4
6
8
10 keV
Fig. 8. EDX analysis of surfaces after corrosion tests in SBF solution: (a) 1 h HA Coated, (b) 168 h TiO2 coated specimens.
1. Hanawa, T., J. Artif. Organs, 2009, vol. 12, p. 73. 2. Manivasagam, G., Dhinasekaran, D., and Rajamanickam, A., Corros. Sci., 2010, vol. 2, p. 40. 3. Songur, M., Celikkan, H., Gokmese, F., et al., J. Appl. Electrochem., 2009, vol. 39, p. 1259. 4. Mudali, U.K., Sridhar, T.M., and Raj, B., SadhanaAcad. P. Eng. S., 2003, vol. 28, p. 601.
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES
Vol. 52
No. 6
2016
CORROSION BEHAVIOUR OF SINGLE AND DOUBLE LAYER 5. Aksakal, B., Gavgali, M., and Dikici, B., J. Mater. Eng. Perform., 2010, vol. 19, p. 894. 6. Aksakal, B., Yildirim, O.S., and Gul, H., J. Fail. Anal. Prev., 2005, vol. 18, p. 101. 7. Cook, Y.S.D., Thomas, K.A., Harding, A.F., et al., Biomaterials, 1987, vol. 8, p. 177. 8. Hiromoto, L.S., Interface (London, U. K.), 2008, vol. 7, p. 41. 9. Amel-Farzad, H., Peivandi, M.T., and Yusof-Sani, S.M.R., Eng. Failure Anal., 2007, vol. 14, p. 1205. 10. Gilbert, J.L., Buckley, C.A., Jacobs, J.J., et al., J. Bone Jt. Surg., 1994, vol. 76, p. 110. 11. Cook, S.D., Barrack, R.L., and Clemow, A.J.T., J. Bone Jt. Surg., 1994, vol. 76, p. 68. 12. Fedrizzi, L., Rossi, S., Bellei, F., et al., Wear, 2002, vol. 253, p. 1173. 13. Liu, X., Chu, P.K., and Ding, C., Mater. Sci. Eng., R, 2004, vol. 47, p. 49. 14. Gaona, M., Lima, R.S., and Marple, B.R., Mater. Sci. Eng.: A, 2007, vol. 458, p. 141. 15. Vijayalakshmi, U., Balamurugan, A., and Rajeshwari, S., Trends Biomater. Artif. Organs, 2005, vol. 18, p. 101. 16. Olmo, N., Mratin, A.I., Salinas, A.J., et al., Biomaterials, 2003, vol. 24, p. 3383. 17. Guehennec, L.L., Soueidan, A., Layrolle, P., et al., Dent. Mater., 2007, vol. 23, p. 844. 18. Huang, Y., Wang, Y., Ning, C., et al., Biomed. Mater., 2007, vol. 2, p. 196. 19. Ishizawa, H. and Ogino, M., J. Mater. Sci., 1999, vol. 34, p. 5893. 20. Balamurugan, A., Kanan, S., and Rajeswari, S., Trends Biomater. Artif. Organs, 2002, vol. 16, p. 18. 21. Krupa, D., Baszkiewicz, J., Kozubowski, J.A., et al., Biomaterials, 2005, vol. 26, p. 2847.
1085
22. Darr, J.A., Guo, Z.X., Raman, V., et al., Chem. Commun., 2004, vol. 6, p. 696. 23. Nelea, V., Ristoscu, C., Chiritescu, C., et al., Appl. Surf. Sci., 2000, vol. 168, p. 127. 24. Shi, J.Z., Chen, C.Z., Yu, H.J., et al., Bull. Mater. Sci., 2008, vol. 31, p. 877. 25. Sobieszczyk, S., Adv. Mater. Sci., 2010, vol. 10, p. 29. 26. Heimann, R.B., Plasma-Spray Coating. Principles and Application, Weinheim: VCH, 1996. 27. Li, H., Khor, K.A., and Cheang, P., Biomaterials, 2002, vol. 23, p. 85. 28. Li, H., Khor, K.A., and Cheang, P., Biomaterials, 2003, vol. 24, p. 949. 29. Nie, X., Leyland, A., and Matthews, A., Surf. Coat. Technol., 2000, vol. 125, p. 407. 30. Ye, F.X., Ohmori, A., Tsumura, T., et al., J. Therm. Spray Technol., 2007, vol. 16, p. 776. 31. Shuai, C., Shaokang, G., Bin, C., et al., Appl. Surf. Sci., 2011, vol. 257, p. 4464. 32. Gurpreet, S., Hazoor, S., and Buta, S.S., Surf. Coat. Technol., 2013, vol. 228, p. 242. 33. Yetim, A.F., Yildiz, F., Alsaran, A., et al., Kovove Mater., 2008, vol. 46, p. 105. 34. Kayali, Y., Prot. Met. Phys. Chem. Surf., 2014, vol. 50, no. 3, p. 412. 35. Jordan, L.R., Betts, A.J., Dahm, K.L., et al., Corros. Sci., 2005, vol. 47, p. 1085. 36. Xu, W., Hu, W.Y., Li, M.H., et al., Trans. Nonferrous Met. Soc. China, 2006, vol. 16, p. 209. 37. Mohan, L., Durgalakshmi, D., Geetha, M., et al., Ceram. Int., 2012, vol. 38, p. 3435. 38. Shuai, C., Shaokang, G., Bin, C., et al., Appl. Surf. Sci., 2011, vol. 257, p. 4464. 39. Tejinder, P.S., Harpreet, S., and Hazoor, S., J. Therm. Spray Technol., 2012, vol. 21, p. 917.
PROTECTION OF METALS AND PHYSICAL CHEMISTRY OF SURFACES
Vol. 52
No. 6
2016
