- Email: [email protected]
Corrosion and tribological properties and impact fatigue behaviors of TiN- and DLC-coated stainless steels in a simulated body fluid environment
Surface & Coatings Technology 205 (2010) 1599–1605
Contents lists available at ScienceDirect
Surface & Coatings Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u r f c o a t
Corrosion and tribological properties and impact fatigue behaviors of TiN- and DLC-coated stainless steels in a simulated body fluid environment L. Wang a,b, J.F. Su a, X. Nie a,⁎ a b
Department of Mechanical, Automotive, & Materials Engineering, University of Windsor, Windsor, Ontario, Canada N9B 3P4 College of Engineering, Zhejiang Normal University, Jinhua, Zhejiang 321004, PR China
a r t i c l e
i n f o
Available online 3 August 2010 Keywords: Coatings Corrosion Tribological property Impact fatigue test Biomedical application
a b s t r a c t In this study, the corrosion and tribological properties of TiN and DLC coatings were investigated in a simulated body fluid (SBF) environment. The ball-on-plate impact tests were conducted on the coatings under a combined force of a 700 N static load and a 700 N dynamic impact load for 10,000 impacting cycles. The results indicated that the TiN and DLC coatings could achieve a higher corrosion polarization resistance and a more stable corrosion potential in the SBF environment than the uncoated stainless steel substrate SS316L. The good corrosion protection performance of TiN could be due to the formation of a Ti–O passive layer on the coating surface, which protected the coating from further corrosion. The superior corrosion property of the DLC coating was likely attributed to its chemical inertness under the SBF condition. The TiN and DLC coatings also exhibited an excellent wear resistance and chemical stability during the sliding tests against a high density polyethylene (HDPE) biomaterial. Compared to the DLC coating, the TiN coating has a better compatibility with the HDPE. However, the impact tests showed that the fatigue cracks and the coating chipping occurred on the TiN coating but not on the DLC coating. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Biomaterials used for load-bearing applications including orthopedic implants, pacemakers, surgical instruments, orthodontic appliances and dental instruments, usually have to withstand some aggressive biomedical conditions. Those biomaterials are normally used in a physiological environment with a pH level of 7.4 and a temperature of 37 °C (98.6 °F). The physiological solution is oxygenated and contains organic components in addition to various salts [1]. The biomaterials are also required to have an excellent mechanical strength and wear resistance [1]. Metals are the most commonly used for the load-bearing biomaterials, among which, the most widely used metallic biomaterials for implants devices are 316L stainless steels, cobalt alloys, commercially pure titanium and Ti–6Al–4V alloys [2–6]. However, these materials suffer from some drawbacks, in case of sustained and long-term use, such as cytotoxicity due to releasing of metallic ions, corrosion and wear. Additionally, in many designs of biomaterial structure, a metal-polyethylene (PE) bearing couple is frequently involved. The wear debris generated during applications of polyethylene may cause substantial negative biological effects such as chronic inflammation, when it is transported to the soft tissue surrounding the implant. Thus, besides corrosion and wear protection
⁎ Corresponding author. E-mail address: [email protected] (X. Nie). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.07.111
properties, the compatibility of biomaterials with the polyethylene material is another important issue to be concerned. PVD and CVD hard ceramic coatings are expected to be the emerging biomaterials for load-bearing medical devices due to their excellent corrosion and wear protection performance. The ceramic coatings TiN, DLC, TiAlN, TiN/TiAlN, TaN and ZrN [7–15] prepared by the cathodic arc method, reactive magnetron sputtering, etc. have been studied on their corrosion resistance, biocompatible characteristics and mechanical properties. Until now, the TiN and diamond-like carbon (DLC) coatings are still considered as the most promising coatings used for load-bearing biomaterials and have been used in orthopaedic prostheses, cardiac valves and dental prostheses [16–18]. Both TiN and a-H:C DLC are found to be biocompatible and have been reported to achieve corrosion protection under most of the biomedical environments [10–12,19–26]. However, the test results in wear and compatibility performances of those coatings against different counter contacting surfaces are rather controversial probably due to different research groups using different experimental setups (pinon-disk, hip or knee simulator, different surface roughness) and different liquids as lubricants. In addition, few works were conducted to investigate the fatigue behavior of coatings under a load condition simulating some special activities such as climbing, stumbling, and jumping. In those cases, an impact load can be involved, and the impact fatigue can be one of the most likely failure mechanisms of the coated-biomaterials. Bearing this in mind, in this study, the corrosion performances of TiN and DLC coatings were evaluated in a simulated body fluid by
1600
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
electrochemical methods. Pin-on-disc sliding wear tests (under a fixed static load) and impact fatigue tests were also conducted. The results of those coatings tested under the simulated biomedical environment and load condition were discussed.
observed using scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) (SEM JOEL 2100) at a 15 kV operating voltage. 2.3. Tribological tests
2. Experimental details 2.1. Preparation of substrates and coatings TiN [27] and a-H:DLC (Diamolith®) coatings [27,28] were prepared using standard commercial processes at Tecvac Ltd. DLC coating was prepared by plasma-assisted chemical vapour deposition (PACVD). Samples were sputter cleaned in an Ar–H2 discharge prior to DLC coating and a thin Si bond layer was first deposited at a thickness of 0.4–0.5 μm. A total pressure of 0.8 Pa was used during deposition and the substrates were R.F. biased to a total power of 500–550 W. The maximum coating temperature did not exceed 300 °C. TiN coating was deposited by electron beam plasma-assisted physical vapour deposition (PAPVD) using a Tecvac IP70 coater. The coating temperature did not exceed 450 °C [27]. AISI 316L stainless steel discs of 30 mm in diameter and 3 mm in thickness with mirror surface finish (Ra b 0.1 μm) were used as the coating substrates. The hardness and reduced elastic modulus measured by nano-indentation tests are 25.5 GPa and 355.1 GPa for the TiN coating [29,30] and 20.5 GPa and 180.0 GPa for the DLC coating, respectively. The thickness of TiN coating is 2 μm, and the thickness of DLC coating is 3 μm. Uncoated AISI 316L stainless steel discs were also polished and cleaned for use as a reference material. 2.2. Corrosion tests The corrosion properties of the uncoated and coated samples were evaluated by two electrochemical methods: the potentiodynamic polarization corrosion test and the corrosion potential monitoring. The potentiodynamic polarization corrosion tests were performed to determine the corrosion rate, which is relevant to the ion releasing rate of the tested material. After the tests, the polarization corrosion resistance (Rp) was calculated using the Tafel-extrapolation method and Stern–Geary equation [31]: Rp =
βa βc 2:3:Icorr ðβa + βc Þ
where βa and βc are the anodic and cathodic Tafel slopes, respectively and Icorr is the corrosion current. Since changes in corrosion potential (Ecorr) can also give an indication of forming and dissolving of passive layer on the top surface of samples, corrosion potential monitoring was also conducted. The corrosion tests were carried out in a three-electrode system test unit with a platinum counter electrode of 1 cm2 and an Ag/AgCl, 3 M KCl electrode as the reference electrode using a SP-150 Potentiostat (Biologic Science Instruments) controlled by a computer. All the electrochemical characterizations were performed at 37 °C in the Hanks’ solution to simulate the human body fluid environment. The solution was prepared using the commercial Hanks’ Balanced Salt (Sigma-Aldrich®). The pH of the solution was carefully adjusted to be at 7.4. Freshly prepared solution was used for each experiment. The composition of the Hanks’ solution used in this study was (in g/l) 8 NaCl, 0.4 KCl, 0.185 CaCl2.2H2O, 0.09767 MgSO4, 0.35 NaHCO3, 1.00 Glucose, 0.06 KH2PO4 and 0.04788 NaH2PO4. In the potentiodynamic polarization corrosion tests, the initial potential was −1.5 V vs. open circuit potential (OCP), and the final potential was 1.5 V vs. Ag/AgCl electrode. The scan rate was 1 mV/s. The corrosion potential monitoring was maintained up to 10 h using the corrosion test unit at an OCP operating condition. The surface morphologies and compositions of samples after corrosion tests were
Tribological behaviors of coatings were characterized by a pin-ondisc tribometer against high density polyethylene (HDPE) balls as pins (5.5 mm in diameter) under boundary lubricated conditions with either distilled water or Hanks’ solution dripping on the coating surface (0.5 ml/2000 revolutions). The sliding distance was 500 m (i.e., 40,000 revolutions), and the normal load was 10 N. The details of material transfer phenomena between coatings and counterface balls and morphologies of wear scars were observed using Fei Quanta 200F SEM with EDX. Since the polyethylene balls are not electrically conductive, the low vacuum (70 Pa) mode was used to observe the worn HDPE ball surface. 2.4. Impact fatigue tests A ball-on-plate impact tester was used for impact fatigue tests of the coatings. The test concept is shown in Fig. 1. The impact ball (AISI 52100 steel ball with the diameter of 10 mm) is driven by a two-way stroke piston with compressed air and the quasi-static driving force was constant (static load, FS) for a given air pressure. The driving force (FS) and dynamic impact force (FI) can be changed by adjusting air pressure and the distance between the impact ball and sample surface, respectively. The frequency of the impacting was 5 Hz. A 700 N static and 700 N dynamic impact load was selected to simulate the impact processes on the load-bearing biomaterials when an average adult (70 kg in weight) was in some relatively intense activities such as climbing, stumbling, jumping etc. 104 cycles of impacts were conducted on each sample. The load calibrations before and after the impact tests were performed using an OMEGA LCKD-500 load cell. 3. Results and discussion 3.1. Electrochemical corrosion properties Fig. 2 shows the potentiodynamic polarization curves of uncoated and coated stainless steel 316 L samples in the SBF solution at 37 °C. The
Fig. 1. Schematic of the impact tester.
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
1601
1.5 TiN 1.1
Potential, V
0.7 DLC 0.3
SS
-0.1 -0.5 -0.9 -1.3 -1.7 1.E-10
1.E-08
1.E-06
1.E-04
1.E-02
Current density, A.cm-2 Fig. 2. Potentiodynamic polarization curves of uncoated and coated SS316L in the simulated body fluid at 37 °C.
polarization data are listed in Table 1. The corrosion test results showed that higher Rp and lower Icorr values were measured for the TiN- and DLC-coated samples than the uncoated SS316L (Rp = 7.63 kΩ cm2 and Icorr = 5.36 μA/cm2). The DLC coating exhibited the highest Rp (1543 kΩ cm2) and lowest Icorr (0.055 μA/cm2) among all the three samples. Since the corrosion rate of a tested sample is inversely and directly proportional to its corrosion polarization resistance (Rp) and corrosion current density (Icorr), respectively, the DLC coating has the lowest calculated corrosion rate based on the potentiodynamic polarization tests. A biomaterial is required to have a low ion release rate in biomedical environments. It may not be easy to exactly measure the ion content released into the body fluid environment, but the electrochemical test can conveniently be conducted to study the corrosion rate through the measurement of corrosion current (Icorr) of a biomaterial. The corrosion rate is relevant to the ion releasing rate of the tested biomaterial. The lower corrosion rate of the sample, the less severe invasion to human body due to reduced metallic ions released from the biomaterial. Therefore, the smaller corrosion currents (Icorr) of the TiN and DLC coatings indicate that the coatings would have a better biocompatibility than the uncoated SS316L. Fig. 3 shows the curves of corrosion potential (Ecorr) vs. testing time for various uncoated and coated samples in the simulated body fluids. The Ecorr of the uncoated SS316L varied during the testing time. The Ecorr was less than −0.1 V at the first 2 h-testing time, then increased gradually to a positive value. After that, the curve fluctuated progressively with the testing time within a range from −0.03 V to +0.03 V. For the TiN coating, in the first half hour of the Ecorr vs. time curve, the Ecorr increased gradually to +0.085 V, then the curve was relatively stable compared to that of the uncoated SS316L. At the beginning stage of the corrosion test, the DLC coating had a Ecorr of +0.1 V then the average Ecorr increased very slowly during the test process and finally reached up to +0.14 V at the end of the corrosion test. However, unlike the curve for the uncoated SS316L, which has broad peaks and valleys (Fig. 3), the curve for the DLC coating presents a spike-like pattern with abrupt peaks and valleys. The SEM observation on the corrosion-tested area indicated
Table 1 Potentiodynamic polarization corrosion data of uncoated and coated samples in a simulated body fluid.
SS TiN DLC
Ecorr (mV)
Icorr (μA/cm2)
βa (mV/dec)
βc (mV/dec)
Rp (kΩ cm2)
−929.6 −158.6 + 4.4
5.359 0.256 0.055
275.4 176.0 334.6
142.8 155.9 469.2
7.63 140.40 1543.99
Fig. 3. 10-hours Ecorr monitoring curves in the simulated body fluid at 37 °C.
that no visible corrosion damages occurred. The EDX analysis showed oxygen (O) element was detected on the uncoated and TiN-coated sample surfaces but no exotic elements could be detected on the DLC coating surface. It can be believed that the fluctuation of Ecorr vs. time curves (Fig. 3) is related to the forming and dissolving of the passive oxide film on the stainless steel surface. When the oxide film forming process is faster than the dissolving process, the Ecorr increases, otherwise, it drops. The oxide forming and dissolving process leads to release metal ions, such as Fe and Cr, which have negative effects on the performance of stainless steel in the biomedical application. In the SBF environment, the TiN coating could however form a stable passive Ti–O layer as indicated by the EDX analysis (not shown here) and the stable Ecorr curve in Fig. 3, and thus reduce the ion release compared to the uncoated stainless steel. To explain the behavior of the Ecorr curve of the DLC coating in Fig. 3 is rather difficult or speculative. The DLC coating was known to comprise sp3 and sp2 hybridized bonds. More diamond-like sp3 bonds in the coating would cause a higher electrode potential. The coating in this work was an H-contained DLC. A loss of H atoms would make the coating have more sp2 bonds, due to the sp3 to sp2 transitions, and thus a lower electrode potential. This appeared as a drop of the voltage on the corrosion potential monitoring curve of the DLC coating in Fig. 3. The H atoms could release as H2 gases or enter into the solution as a form of H+ ions after the electrochemical reaction occurred on the coating surface and at the same time generate electrons. Adjacent to the surface, the concentration of H+ ions being the oxidizing agent would increase as a result of the electrochemical reaction, and thus the overpotential (i.e., the voltage spike) was shown on the curve based on the Nernst equation [32]. The increased H+ ions could reversely receive the electrons from the DLC coating surfaces and perform H2 gas evolutions and thus reduce the ion concentration (and the overpotential). These phenomena would be a dynamic process. However, this significant release of H atoms from the DLC coating surface should be started as a localized and discrete manner, since the voltage variation spikes were apart as shown in the curve. Careful examination of the spikes on the curve for the DLC coating by magnifying its each spike (Fig. 3) found that every spike contained a number of ups and downs but it always started with down. This fact may support the speculation described above. The chemical element release phenomena were also observed in a reference [33] where the nitrogen release from amorphous carbon nitride (a-CNx) films was reported after the electrochemical pretreatment. 3.2. Pin-on-disc tribotests Fig. 4 shows the dynamic coefficient of frictions (cofs) of the uncoated and coated samples during the tests. Fig. 5 and its corresponding insets are the SEM micrographs of the wear tracks and HDPE balls after sliding tests under the two lubricant conditions. With distilled water (DW), the cof curve (Fig. 4(a)) of uncoated
1602
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
Fig. 4. Dynamic COF curves of (a, b) uncoated, (c, d) TiN- and (e, f) DLC-coated SS316L against HDPE balls with either (a, c, e) distilled water or (b, d, f) SBF.
SS316L presents a slip-stick behavior and the average cof is about 0.16. The average cof of the SS316L under the SBF lubrication is about 0.14, but the cof curve (Fig. 4(b)) fluctuates more severely than that with DW and the up and down range is ±0.15. On the wear track of the uncoated SS316L after the wear test with DW (Fig. 5(a)), no surface wear or material transferring can be observed. In the wear track of the SS316L after the sliding test with SBF (Fig. 5(b)), there is a large amount of accumulated materials. The main elements of these materials are C, O and some elements from the steel alloy and SBF, which were detected by the EDX. When sliding in the SBF, more corrosion likely occurred at the steel surface compared to the test condition with DW. The accumulated materials were the corrosion products with some polymer material transferred from the counterface ball, which accelerated the wear of counterface ball and therefore the ball had more wear loss after sliding against the SS316L with SBF (inset in Fig. 5(b)) than with DW (inset in Fig. 5(a)). Fig. 4(c, d) shows the dynamic cofs of TiN-coated SS316L samples during the sliding wear tests against HDPE counterface balls under DW and SBF. With DW and SBF, both cof curves showed slip-stick behavior and the average cof values were similar which is about 0.1. The SEM observation of wear tracks on the TiN coating after sliding tests with DW and SBF (Fig. 5(c, d), respectively) indicated that both wear tracks had a similar morphology and under both conditions, no obvious wear but some HDPE material smears existed on the wear tracks. The balls under DW and SBF (insets in Fig. 5(c, d), respectively) had a similar wear loss which again suggests that the TiN coating was relatively stable in SBF and besides the lubricating/cooling effect of water, the electrochemical effect of SBF on the TiN coating's tribological properties was limited. The curves of dynamic cofs of DLC-coated SS316L samples (Fig. 4 (e, f)) showed that the average cofs under the two conditions were
similar, i.e., ~ 0.35. SEM micrographs of wear tracks on DLC coatings (Fig. 5(e, f)) showed that both wear tracks were very smooth without visible wear but some loosen polymer particles were transferred from the balls. The obvious imprints on the SEM micrographs were due to the uniform and thin transferring layer from the counterface ball. The wear losses of the balls after the tests with DW and SBF were similar (insets in Fig. 5(e, f)). The cof curves and SEM morphology observations indicate that the DLC coating was stable in SBF and the effect of body fluid solution on the tribological properties was also trivial. Based on the observations above, under the SBF environment, the uncoated steel was corroded to some extent and the corrosion products caused the accelerated wear of counterface balls, compared to the coated ones. For the case of coatings, the ball wear loss was larger after the tests on the DLC coating than on the TiN coating, which suggests that the carbon-based HDPE polymer against the carbonbased DLC coating may not be a good combinative coupling for the sliding contact. The particles released from the counter ball would also cause acute or chronic adverse biological reactions in human body. Hence, the HDPE may be suitable to be used as a contact surface biomaterial for the TiN coating. However, for the DLC coating, it may be more appropriate for a non-polymer-based material to be selected as the counterface material. 3.3. Impact tests Fig. 6(a) shows the load curve during one impact cycle under 700 N FS and 700 N FI, which depicts that the process of each impact cycle has three stages, i.e., impact loading stage, vibrating stage and static loading stage. When the ball indenter hits the coating surface for the first time,
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
1603
Fig. 5. SEM micrographs of wear tracks on (a, b) uncoated, (c, d) TiN-coated and (e, f) DLC-coated SS316L. The insets in each micrograph show the corresponding counterface HDPE balls after sliding wear tests with (a, c, e) distilled water and (b, d, f) SBF.
the highest peak of the load arises which is the effective impact load (FI). After the ball completed the first impact against the coating surface, a few times of the rebounding and impacting occurred, which can be detected by the load cell and recorded as a series of vibrating signal in the load vs. time curve (Fig. 6(a)). Each rebound process is actually an impact process with decreasing impact energy between the two contact surfaces. After the rebound stops, the load continues to reach up to the set-up static load (FS), then the unload process follows. Fig. 6(b–e) shows the micrographs of coatings after impact tests. The impact crater on the TiN coating was presented in Fig. 6(b, c). In the peripheral zone, a large amount of circular cracks were observed which indicated the cohesive failure had occurred. In the central and intermediate zones (Fig. 6(c)) of the crater, localized delaminations of the TiN coating (adhesive failure) occurred likely due to the shear stress that arose from the plastic strain of the substrate underneath the crater regions. The DLC coating presented a different morphology after the impact test (Fig. 6(d, e)). After 104 impacts, no cohesive or adhesive failure can be observed, but some material has transferred from the counterface steel ball and attached onto the crater surface (Fig. 6(e)).
Thus, the impact test results showed that the DLC had a higher impact fatigue resistance than the TiN coating. This finding is significant because DLC coatings have an upward trend to be used as biomaterials that need to withstand impact forces during the applications. 4. Conclusions The results of potentiodynamic polarization tests and corrosion potential vs. testing time (10 h) indicated that TiN and DLC coatings could achieve a higher corrosion polarization resistance and relatively stable corrosion potential in the SBF environment than the uncoated SS316L. Therefore, the coated samples would have a lower corrosion and metallic ion releasing rate. The superior corrosion protection performance of TiN was due to formation of the Ti–O passive layer on the coating surface, which protects the coating from further corrosion. The excellent anticorrosion property of DLC coating was attributed to its chemical inertness in the SBF environment. The pin-on-disc tribotests indicated that the uncoated SS316 could achieve a good compatibility with the HDPE material at the DW
1604
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
Fig. 6. (a) Load vs. time during one impact under FS = 700 N, FI = 700 N. (b-e) are SEM micrographs of surfaces on coatings (b, c) TiN and (d, e) DLC after impact tests, respectively and (c, e) are the corresponding magnified images of (b, d).
condition. However, when sliding in the SBF media, the uncoated steel was corroded to some extent, and the corrosion products accelerated the wear of counterface balls and caused the material transferring. The HDPE ball against the SS316L sample in the SBF test condition had the highest wear loss. The TiN and DLC coatings improved the compatibility with the HDPE material and reduced the ball material loss. The electrochemical effects of the SBF media on the tribological properties of the TiN and DLC coatings were limited. After the 104 cycles’ impact test with a 700 N impact and 700 N static load for each cycle, impact fatigue occurred on the TiN coating. However, no impact fatigue damage exhibited on the DLC coating except for a small amount of material transferring from the impact steel ball.
Under the conditions of this study, the TiN- and DLC-coated SS316L samples showed a great improvement in corrosion and wear protection properties. Moreover, the coated samples have a better compatibility with the HDPE material compared with the uncoated one, which reduces the HDPE particle debris and therefore reduce the negative effects caused by the particles. While the TiN coating can achieve a better compatibility with the HDPE material than the DLC coating, the DLC coating has a much better impact fatigue resistance than the TiN coating. Both TiN and DLC coatings can be used as an excellent biomaterial although their performances were different to some extent. In terms of a counterface material, the HDPE seems suitable for the TiN coating. However, for the DLC coating, it may be more appropriate for a non-polymer-based material to be selected as the counterface material.
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
Acknowledgements L. Wang would like to acknowledge NSERC for the award of a Canada Graduate Scholarship. The authors also would like to thank the Tecvac Ltd. for the provision of PVD and CVD coatings. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
J.R. Davis, ASM International, 2003, p. 12. C.M. Agrawal, JOM-J. Min. Met. Mater. Soc. 50 (1998) 31. M. Niinomi, J. Artif. Organs 11 (2008) 105. C.V. Vidal, A.I. Munoz, Corros. Sci. 50 (2008) 1954. D. Bombac, M. Brojan, P. Fajfar, F. Kosel, R. Turk, RMZ—Mater. Geoenviron. 54 (2007) 471. M. Niinomi, Metall. Mater. Trans. A—Phys. Metall. Mater. Sci. 33 (2002) 477. R. Hubler, Surf. Coat. Technol. 116 (1999) 1111. J. Park, D.J. Kim, Y.K. Kim, K.H. Lee, H. Lee, S. Ahn, Thin Solid Films 435 (2003) 102. A. Grill, Diamond Relat. Mater. 12 (2003) 166. R.K. Roy, K.R. Lee, J. Biomed. Mater. Res. B—Appl. Biomater. 83B (2007) 72. G. Dearnaley, J.H. Arps, Surf. Coat. Technol. 200 (2005) 2518. R. Hauert, Diamond Relat. Mater. 12 (2003) 583. M. Braic, M. Balaceanu, V. Braic, A. Vladescu, G. Pavelescu, M. Albulescu, Surf. Coat. Technol. 200 (2005) 1014. R. Hubler, A. Cozza, T.L. Marcondes, R.B. Souza, F.F. Fiori, Surf. Coat. Technol. 142– 144 (2001) 1078. Y.X. Leng, H. Sun, P. Yang, J.Y. Chen, J. Wang, G.J. Wan, N. Huang, X.B. Tian, L.P. Wang, P.K. Chu, Thin Solid Films 398–399 (2001) 471. A. Wisbey, P.J. Gregson, M. Tuke, Biomaterials 8 (1987) 477.
1605
[17] O. Knotek, F. Loffler, K. Weitkamp, Surf. Coat. Technol. 55 (1992) 536. [18] P.V. Kola, S. Daniels, D.C. Cameron, M.S.J. Hashmi, J. Mater. Process. Technol. 56 (1996) 422. [19] H. Behrndt, A. Lunk, Mater. Sci. Eng. A—Struct. Mater. Prop. Microstruc. Proc. 139 (1991) 58. [20] J. Zhao, L. Li, D.J. Li, H.Q. Gu, J. Adhes. Sci. Technol. 18 (2004) 1003. [21] A. Kamali, R. Farrar, P. Hatto, M. Stone, J. Fisher, Proc. Inst. Mech. Eng. Part J J. Eng. Tribol. 219 (2005) 41. [22] M. Hoseini, A. Jedenmalm, A. Boldizar, Wear 264 (2008) 958. [23] F.Z. Cui, D.J. Li, Surf. Coat. Technol. 131 (2000) 481. [24] M. Vojs, E. Zdravecka, M. Marton, P. Bohac, L. Franta, M. Vesely, Microelectron. J. 40 (2009) 650. [25] D. Sheeja, B.K. Tay, X. Shi, S.P. Lau, C. Daniel, S.M. Krishnan, L.N. Nung, Diamond Relat. Mater. 10 (2001) 1043. [26] D. Sheeja, B.K. Tay, S.P. Lau, L.N. Nung, Surf. Coat. Technol. 146–147 (2001) 410. [27] J.C. Avelar-Batista, E. Spain, G.G. Fuentes, A. Sola, R. Rodriguez, J. Housden, Surf. Coat. Technol. 201 (2006) 4335. [28] S.D.A. Lawes, M.E. Fitzpatrick, S.V. Hainsworth, J. Phys. D-Appl. Phys. 40 (2007) 5427. [29] L. Wang, X. Nie, J. Housden, E. Spain, J.C. Jiang, E.I. Meletis, A. Leyland, A. Matthews, Surf. Coat. Technol. 203 (2008) 816. [30] L. Wang, D.O. Northwood, X. Nie, J. Housden, E. Spain, A. Leyland, A. Mathews, J. Power Sources 195 (2010) 3814. [31] H.S. Khatak, B. Raj (Eds.), Corrosion of Austenitic Stainless Steels, Woodhead Publishing Limited, Cambridge, 2002, p. 43. [32] J.C. Kotz, P.M. Treichel, G.C. Weaver, Chemistry and chemical reactivity, Thomson Leaming Inc., Belmont, 2006, p. 975. [33] H. Cachet, C. Debiemme-Chouvy, C. Deslouis, A. Lagrini, V. Vivier, Surf. Interface Anal. 38 (2006) 719.
Contents lists available at ScienceDirect
Surface & Coatings Technology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s u r f c o a t
Corrosion and tribological properties and impact fatigue behaviors of TiN- and DLC-coated stainless steels in a simulated body fluid environment L. Wang a,b, J.F. Su a, X. Nie a,⁎ a b
Department of Mechanical, Automotive, & Materials Engineering, University of Windsor, Windsor, Ontario, Canada N9B 3P4 College of Engineering, Zhejiang Normal University, Jinhua, Zhejiang 321004, PR China
a r t i c l e
i n f o
Available online 3 August 2010 Keywords: Coatings Corrosion Tribological property Impact fatigue test Biomedical application
a b s t r a c t In this study, the corrosion and tribological properties of TiN and DLC coatings were investigated in a simulated body fluid (SBF) environment. The ball-on-plate impact tests were conducted on the coatings under a combined force of a 700 N static load and a 700 N dynamic impact load for 10,000 impacting cycles. The results indicated that the TiN and DLC coatings could achieve a higher corrosion polarization resistance and a more stable corrosion potential in the SBF environment than the uncoated stainless steel substrate SS316L. The good corrosion protection performance of TiN could be due to the formation of a Ti–O passive layer on the coating surface, which protected the coating from further corrosion. The superior corrosion property of the DLC coating was likely attributed to its chemical inertness under the SBF condition. The TiN and DLC coatings also exhibited an excellent wear resistance and chemical stability during the sliding tests against a high density polyethylene (HDPE) biomaterial. Compared to the DLC coating, the TiN coating has a better compatibility with the HDPE. However, the impact tests showed that the fatigue cracks and the coating chipping occurred on the TiN coating but not on the DLC coating. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Biomaterials used for load-bearing applications including orthopedic implants, pacemakers, surgical instruments, orthodontic appliances and dental instruments, usually have to withstand some aggressive biomedical conditions. Those biomaterials are normally used in a physiological environment with a pH level of 7.4 and a temperature of 37 °C (98.6 °F). The physiological solution is oxygenated and contains organic components in addition to various salts [1]. The biomaterials are also required to have an excellent mechanical strength and wear resistance [1]. Metals are the most commonly used for the load-bearing biomaterials, among which, the most widely used metallic biomaterials for implants devices are 316L stainless steels, cobalt alloys, commercially pure titanium and Ti–6Al–4V alloys [2–6]. However, these materials suffer from some drawbacks, in case of sustained and long-term use, such as cytotoxicity due to releasing of metallic ions, corrosion and wear. Additionally, in many designs of biomaterial structure, a metal-polyethylene (PE) bearing couple is frequently involved. The wear debris generated during applications of polyethylene may cause substantial negative biological effects such as chronic inflammation, when it is transported to the soft tissue surrounding the implant. Thus, besides corrosion and wear protection
⁎ Corresponding author. E-mail address: [email protected] (X. Nie). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.07.111
properties, the compatibility of biomaterials with the polyethylene material is another important issue to be concerned. PVD and CVD hard ceramic coatings are expected to be the emerging biomaterials for load-bearing medical devices due to their excellent corrosion and wear protection performance. The ceramic coatings TiN, DLC, TiAlN, TiN/TiAlN, TaN and ZrN [7–15] prepared by the cathodic arc method, reactive magnetron sputtering, etc. have been studied on their corrosion resistance, biocompatible characteristics and mechanical properties. Until now, the TiN and diamond-like carbon (DLC) coatings are still considered as the most promising coatings used for load-bearing biomaterials and have been used in orthopaedic prostheses, cardiac valves and dental prostheses [16–18]. Both TiN and a-H:C DLC are found to be biocompatible and have been reported to achieve corrosion protection under most of the biomedical environments [10–12,19–26]. However, the test results in wear and compatibility performances of those coatings against different counter contacting surfaces are rather controversial probably due to different research groups using different experimental setups (pinon-disk, hip or knee simulator, different surface roughness) and different liquids as lubricants. In addition, few works were conducted to investigate the fatigue behavior of coatings under a load condition simulating some special activities such as climbing, stumbling, and jumping. In those cases, an impact load can be involved, and the impact fatigue can be one of the most likely failure mechanisms of the coated-biomaterials. Bearing this in mind, in this study, the corrosion performances of TiN and DLC coatings were evaluated in a simulated body fluid by
1600
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
electrochemical methods. Pin-on-disc sliding wear tests (under a fixed static load) and impact fatigue tests were also conducted. The results of those coatings tested under the simulated biomedical environment and load condition were discussed.
observed using scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX) (SEM JOEL 2100) at a 15 kV operating voltage. 2.3. Tribological tests
2. Experimental details 2.1. Preparation of substrates and coatings TiN [27] and a-H:DLC (Diamolith®) coatings [27,28] were prepared using standard commercial processes at Tecvac Ltd. DLC coating was prepared by plasma-assisted chemical vapour deposition (PACVD). Samples were sputter cleaned in an Ar–H2 discharge prior to DLC coating and a thin Si bond layer was first deposited at a thickness of 0.4–0.5 μm. A total pressure of 0.8 Pa was used during deposition and the substrates were R.F. biased to a total power of 500–550 W. The maximum coating temperature did not exceed 300 °C. TiN coating was deposited by electron beam plasma-assisted physical vapour deposition (PAPVD) using a Tecvac IP70 coater. The coating temperature did not exceed 450 °C [27]. AISI 316L stainless steel discs of 30 mm in diameter and 3 mm in thickness with mirror surface finish (Ra b 0.1 μm) were used as the coating substrates. The hardness and reduced elastic modulus measured by nano-indentation tests are 25.5 GPa and 355.1 GPa for the TiN coating [29,30] and 20.5 GPa and 180.0 GPa for the DLC coating, respectively. The thickness of TiN coating is 2 μm, and the thickness of DLC coating is 3 μm. Uncoated AISI 316L stainless steel discs were also polished and cleaned for use as a reference material. 2.2. Corrosion tests The corrosion properties of the uncoated and coated samples were evaluated by two electrochemical methods: the potentiodynamic polarization corrosion test and the corrosion potential monitoring. The potentiodynamic polarization corrosion tests were performed to determine the corrosion rate, which is relevant to the ion releasing rate of the tested material. After the tests, the polarization corrosion resistance (Rp) was calculated using the Tafel-extrapolation method and Stern–Geary equation [31]: Rp =
βa βc 2:3:Icorr ðβa + βc Þ
where βa and βc are the anodic and cathodic Tafel slopes, respectively and Icorr is the corrosion current. Since changes in corrosion potential (Ecorr) can also give an indication of forming and dissolving of passive layer on the top surface of samples, corrosion potential monitoring was also conducted. The corrosion tests were carried out in a three-electrode system test unit with a platinum counter electrode of 1 cm2 and an Ag/AgCl, 3 M KCl electrode as the reference electrode using a SP-150 Potentiostat (Biologic Science Instruments) controlled by a computer. All the electrochemical characterizations were performed at 37 °C in the Hanks’ solution to simulate the human body fluid environment. The solution was prepared using the commercial Hanks’ Balanced Salt (Sigma-Aldrich®). The pH of the solution was carefully adjusted to be at 7.4. Freshly prepared solution was used for each experiment. The composition of the Hanks’ solution used in this study was (in g/l) 8 NaCl, 0.4 KCl, 0.185 CaCl2.2H2O, 0.09767 MgSO4, 0.35 NaHCO3, 1.00 Glucose, 0.06 KH2PO4 and 0.04788 NaH2PO4. In the potentiodynamic polarization corrosion tests, the initial potential was −1.5 V vs. open circuit potential (OCP), and the final potential was 1.5 V vs. Ag/AgCl electrode. The scan rate was 1 mV/s. The corrosion potential monitoring was maintained up to 10 h using the corrosion test unit at an OCP operating condition. The surface morphologies and compositions of samples after corrosion tests were
Tribological behaviors of coatings were characterized by a pin-ondisc tribometer against high density polyethylene (HDPE) balls as pins (5.5 mm in diameter) under boundary lubricated conditions with either distilled water or Hanks’ solution dripping on the coating surface (0.5 ml/2000 revolutions). The sliding distance was 500 m (i.e., 40,000 revolutions), and the normal load was 10 N. The details of material transfer phenomena between coatings and counterface balls and morphologies of wear scars were observed using Fei Quanta 200F SEM with EDX. Since the polyethylene balls are not electrically conductive, the low vacuum (70 Pa) mode was used to observe the worn HDPE ball surface. 2.4. Impact fatigue tests A ball-on-plate impact tester was used for impact fatigue tests of the coatings. The test concept is shown in Fig. 1. The impact ball (AISI 52100 steel ball with the diameter of 10 mm) is driven by a two-way stroke piston with compressed air and the quasi-static driving force was constant (static load, FS) for a given air pressure. The driving force (FS) and dynamic impact force (FI) can be changed by adjusting air pressure and the distance between the impact ball and sample surface, respectively. The frequency of the impacting was 5 Hz. A 700 N static and 700 N dynamic impact load was selected to simulate the impact processes on the load-bearing biomaterials when an average adult (70 kg in weight) was in some relatively intense activities such as climbing, stumbling, jumping etc. 104 cycles of impacts were conducted on each sample. The load calibrations before and after the impact tests were performed using an OMEGA LCKD-500 load cell. 3. Results and discussion 3.1. Electrochemical corrosion properties Fig. 2 shows the potentiodynamic polarization curves of uncoated and coated stainless steel 316 L samples in the SBF solution at 37 °C. The
Fig. 1. Schematic of the impact tester.
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
1601
1.5 TiN 1.1
Potential, V
0.7 DLC 0.3
SS
-0.1 -0.5 -0.9 -1.3 -1.7 1.E-10
1.E-08
1.E-06
1.E-04
1.E-02
Current density, A.cm-2 Fig. 2. Potentiodynamic polarization curves of uncoated and coated SS316L in the simulated body fluid at 37 °C.
polarization data are listed in Table 1. The corrosion test results showed that higher Rp and lower Icorr values were measured for the TiN- and DLC-coated samples than the uncoated SS316L (Rp = 7.63 kΩ cm2 and Icorr = 5.36 μA/cm2). The DLC coating exhibited the highest Rp (1543 kΩ cm2) and lowest Icorr (0.055 μA/cm2) among all the three samples. Since the corrosion rate of a tested sample is inversely and directly proportional to its corrosion polarization resistance (Rp) and corrosion current density (Icorr), respectively, the DLC coating has the lowest calculated corrosion rate based on the potentiodynamic polarization tests. A biomaterial is required to have a low ion release rate in biomedical environments. It may not be easy to exactly measure the ion content released into the body fluid environment, but the electrochemical test can conveniently be conducted to study the corrosion rate through the measurement of corrosion current (Icorr) of a biomaterial. The corrosion rate is relevant to the ion releasing rate of the tested biomaterial. The lower corrosion rate of the sample, the less severe invasion to human body due to reduced metallic ions released from the biomaterial. Therefore, the smaller corrosion currents (Icorr) of the TiN and DLC coatings indicate that the coatings would have a better biocompatibility than the uncoated SS316L. Fig. 3 shows the curves of corrosion potential (Ecorr) vs. testing time for various uncoated and coated samples in the simulated body fluids. The Ecorr of the uncoated SS316L varied during the testing time. The Ecorr was less than −0.1 V at the first 2 h-testing time, then increased gradually to a positive value. After that, the curve fluctuated progressively with the testing time within a range from −0.03 V to +0.03 V. For the TiN coating, in the first half hour of the Ecorr vs. time curve, the Ecorr increased gradually to +0.085 V, then the curve was relatively stable compared to that of the uncoated SS316L. At the beginning stage of the corrosion test, the DLC coating had a Ecorr of +0.1 V then the average Ecorr increased very slowly during the test process and finally reached up to +0.14 V at the end of the corrosion test. However, unlike the curve for the uncoated SS316L, which has broad peaks and valleys (Fig. 3), the curve for the DLC coating presents a spike-like pattern with abrupt peaks and valleys. The SEM observation on the corrosion-tested area indicated
Table 1 Potentiodynamic polarization corrosion data of uncoated and coated samples in a simulated body fluid.
SS TiN DLC
Ecorr (mV)
Icorr (μA/cm2)
βa (mV/dec)
βc (mV/dec)
Rp (kΩ cm2)
−929.6 −158.6 + 4.4
5.359 0.256 0.055
275.4 176.0 334.6
142.8 155.9 469.2
7.63 140.40 1543.99
Fig. 3. 10-hours Ecorr monitoring curves in the simulated body fluid at 37 °C.
that no visible corrosion damages occurred. The EDX analysis showed oxygen (O) element was detected on the uncoated and TiN-coated sample surfaces but no exotic elements could be detected on the DLC coating surface. It can be believed that the fluctuation of Ecorr vs. time curves (Fig. 3) is related to the forming and dissolving of the passive oxide film on the stainless steel surface. When the oxide film forming process is faster than the dissolving process, the Ecorr increases, otherwise, it drops. The oxide forming and dissolving process leads to release metal ions, such as Fe and Cr, which have negative effects on the performance of stainless steel in the biomedical application. In the SBF environment, the TiN coating could however form a stable passive Ti–O layer as indicated by the EDX analysis (not shown here) and the stable Ecorr curve in Fig. 3, and thus reduce the ion release compared to the uncoated stainless steel. To explain the behavior of the Ecorr curve of the DLC coating in Fig. 3 is rather difficult or speculative. The DLC coating was known to comprise sp3 and sp2 hybridized bonds. More diamond-like sp3 bonds in the coating would cause a higher electrode potential. The coating in this work was an H-contained DLC. A loss of H atoms would make the coating have more sp2 bonds, due to the sp3 to sp2 transitions, and thus a lower electrode potential. This appeared as a drop of the voltage on the corrosion potential monitoring curve of the DLC coating in Fig. 3. The H atoms could release as H2 gases or enter into the solution as a form of H+ ions after the electrochemical reaction occurred on the coating surface and at the same time generate electrons. Adjacent to the surface, the concentration of H+ ions being the oxidizing agent would increase as a result of the electrochemical reaction, and thus the overpotential (i.e., the voltage spike) was shown on the curve based on the Nernst equation [32]. The increased H+ ions could reversely receive the electrons from the DLC coating surfaces and perform H2 gas evolutions and thus reduce the ion concentration (and the overpotential). These phenomena would be a dynamic process. However, this significant release of H atoms from the DLC coating surface should be started as a localized and discrete manner, since the voltage variation spikes were apart as shown in the curve. Careful examination of the spikes on the curve for the DLC coating by magnifying its each spike (Fig. 3) found that every spike contained a number of ups and downs but it always started with down. This fact may support the speculation described above. The chemical element release phenomena were also observed in a reference [33] where the nitrogen release from amorphous carbon nitride (a-CNx) films was reported after the electrochemical pretreatment. 3.2. Pin-on-disc tribotests Fig. 4 shows the dynamic coefficient of frictions (cofs) of the uncoated and coated samples during the tests. Fig. 5 and its corresponding insets are the SEM micrographs of the wear tracks and HDPE balls after sliding tests under the two lubricant conditions. With distilled water (DW), the cof curve (Fig. 4(a)) of uncoated
1602
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
Fig. 4. Dynamic COF curves of (a, b) uncoated, (c, d) TiN- and (e, f) DLC-coated SS316L against HDPE balls with either (a, c, e) distilled water or (b, d, f) SBF.
SS316L presents a slip-stick behavior and the average cof is about 0.16. The average cof of the SS316L under the SBF lubrication is about 0.14, but the cof curve (Fig. 4(b)) fluctuates more severely than that with DW and the up and down range is ±0.15. On the wear track of the uncoated SS316L after the wear test with DW (Fig. 5(a)), no surface wear or material transferring can be observed. In the wear track of the SS316L after the sliding test with SBF (Fig. 5(b)), there is a large amount of accumulated materials. The main elements of these materials are C, O and some elements from the steel alloy and SBF, which were detected by the EDX. When sliding in the SBF, more corrosion likely occurred at the steel surface compared to the test condition with DW. The accumulated materials were the corrosion products with some polymer material transferred from the counterface ball, which accelerated the wear of counterface ball and therefore the ball had more wear loss after sliding against the SS316L with SBF (inset in Fig. 5(b)) than with DW (inset in Fig. 5(a)). Fig. 4(c, d) shows the dynamic cofs of TiN-coated SS316L samples during the sliding wear tests against HDPE counterface balls under DW and SBF. With DW and SBF, both cof curves showed slip-stick behavior and the average cof values were similar which is about 0.1. The SEM observation of wear tracks on the TiN coating after sliding tests with DW and SBF (Fig. 5(c, d), respectively) indicated that both wear tracks had a similar morphology and under both conditions, no obvious wear but some HDPE material smears existed on the wear tracks. The balls under DW and SBF (insets in Fig. 5(c, d), respectively) had a similar wear loss which again suggests that the TiN coating was relatively stable in SBF and besides the lubricating/cooling effect of water, the electrochemical effect of SBF on the TiN coating's tribological properties was limited. The curves of dynamic cofs of DLC-coated SS316L samples (Fig. 4 (e, f)) showed that the average cofs under the two conditions were
similar, i.e., ~ 0.35. SEM micrographs of wear tracks on DLC coatings (Fig. 5(e, f)) showed that both wear tracks were very smooth without visible wear but some loosen polymer particles were transferred from the balls. The obvious imprints on the SEM micrographs were due to the uniform and thin transferring layer from the counterface ball. The wear losses of the balls after the tests with DW and SBF were similar (insets in Fig. 5(e, f)). The cof curves and SEM morphology observations indicate that the DLC coating was stable in SBF and the effect of body fluid solution on the tribological properties was also trivial. Based on the observations above, under the SBF environment, the uncoated steel was corroded to some extent and the corrosion products caused the accelerated wear of counterface balls, compared to the coated ones. For the case of coatings, the ball wear loss was larger after the tests on the DLC coating than on the TiN coating, which suggests that the carbon-based HDPE polymer against the carbonbased DLC coating may not be a good combinative coupling for the sliding contact. The particles released from the counter ball would also cause acute or chronic adverse biological reactions in human body. Hence, the HDPE may be suitable to be used as a contact surface biomaterial for the TiN coating. However, for the DLC coating, it may be more appropriate for a non-polymer-based material to be selected as the counterface material. 3.3. Impact tests Fig. 6(a) shows the load curve during one impact cycle under 700 N FS and 700 N FI, which depicts that the process of each impact cycle has three stages, i.e., impact loading stage, vibrating stage and static loading stage. When the ball indenter hits the coating surface for the first time,
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
1603
Fig. 5. SEM micrographs of wear tracks on (a, b) uncoated, (c, d) TiN-coated and (e, f) DLC-coated SS316L. The insets in each micrograph show the corresponding counterface HDPE balls after sliding wear tests with (a, c, e) distilled water and (b, d, f) SBF.
the highest peak of the load arises which is the effective impact load (FI). After the ball completed the first impact against the coating surface, a few times of the rebounding and impacting occurred, which can be detected by the load cell and recorded as a series of vibrating signal in the load vs. time curve (Fig. 6(a)). Each rebound process is actually an impact process with decreasing impact energy between the two contact surfaces. After the rebound stops, the load continues to reach up to the set-up static load (FS), then the unload process follows. Fig. 6(b–e) shows the micrographs of coatings after impact tests. The impact crater on the TiN coating was presented in Fig. 6(b, c). In the peripheral zone, a large amount of circular cracks were observed which indicated the cohesive failure had occurred. In the central and intermediate zones (Fig. 6(c)) of the crater, localized delaminations of the TiN coating (adhesive failure) occurred likely due to the shear stress that arose from the plastic strain of the substrate underneath the crater regions. The DLC coating presented a different morphology after the impact test (Fig. 6(d, e)). After 104 impacts, no cohesive or adhesive failure can be observed, but some material has transferred from the counterface steel ball and attached onto the crater surface (Fig. 6(e)).
Thus, the impact test results showed that the DLC had a higher impact fatigue resistance than the TiN coating. This finding is significant because DLC coatings have an upward trend to be used as biomaterials that need to withstand impact forces during the applications. 4. Conclusions The results of potentiodynamic polarization tests and corrosion potential vs. testing time (10 h) indicated that TiN and DLC coatings could achieve a higher corrosion polarization resistance and relatively stable corrosion potential in the SBF environment than the uncoated SS316L. Therefore, the coated samples would have a lower corrosion and metallic ion releasing rate. The superior corrosion protection performance of TiN was due to formation of the Ti–O passive layer on the coating surface, which protects the coating from further corrosion. The excellent anticorrosion property of DLC coating was attributed to its chemical inertness in the SBF environment. The pin-on-disc tribotests indicated that the uncoated SS316 could achieve a good compatibility with the HDPE material at the DW
1604
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
Fig. 6. (a) Load vs. time during one impact under FS = 700 N, FI = 700 N. (b-e) are SEM micrographs of surfaces on coatings (b, c) TiN and (d, e) DLC after impact tests, respectively and (c, e) are the corresponding magnified images of (b, d).
condition. However, when sliding in the SBF media, the uncoated steel was corroded to some extent, and the corrosion products accelerated the wear of counterface balls and caused the material transferring. The HDPE ball against the SS316L sample in the SBF test condition had the highest wear loss. The TiN and DLC coatings improved the compatibility with the HDPE material and reduced the ball material loss. The electrochemical effects of the SBF media on the tribological properties of the TiN and DLC coatings were limited. After the 104 cycles’ impact test with a 700 N impact and 700 N static load for each cycle, impact fatigue occurred on the TiN coating. However, no impact fatigue damage exhibited on the DLC coating except for a small amount of material transferring from the impact steel ball.
Under the conditions of this study, the TiN- and DLC-coated SS316L samples showed a great improvement in corrosion and wear protection properties. Moreover, the coated samples have a better compatibility with the HDPE material compared with the uncoated one, which reduces the HDPE particle debris and therefore reduce the negative effects caused by the particles. While the TiN coating can achieve a better compatibility with the HDPE material than the DLC coating, the DLC coating has a much better impact fatigue resistance than the TiN coating. Both TiN and DLC coatings can be used as an excellent biomaterial although their performances were different to some extent. In terms of a counterface material, the HDPE seems suitable for the TiN coating. However, for the DLC coating, it may be more appropriate for a non-polymer-based material to be selected as the counterface material.
L. Wang et al. / Surface & Coatings Technology 205 (2010) 1599–1605
Acknowledgements L. Wang would like to acknowledge NSERC for the award of a Canada Graduate Scholarship. The authors also would like to thank the Tecvac Ltd. for the provision of PVD and CVD coatings. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
J.R. Davis, ASM International, 2003, p. 12. C.M. Agrawal, JOM-J. Min. Met. Mater. Soc. 50 (1998) 31. M. Niinomi, J. Artif. Organs 11 (2008) 105. C.V. Vidal, A.I. Munoz, Corros. Sci. 50 (2008) 1954. D. Bombac, M. Brojan, P. Fajfar, F. Kosel, R. Turk, RMZ—Mater. Geoenviron. 54 (2007) 471. M. Niinomi, Metall. Mater. Trans. A—Phys. Metall. Mater. Sci. 33 (2002) 477. R. Hubler, Surf. Coat. Technol. 116 (1999) 1111. J. Park, D.J. Kim, Y.K. Kim, K.H. Lee, H. Lee, S. Ahn, Thin Solid Films 435 (2003) 102. A. Grill, Diamond Relat. Mater. 12 (2003) 166. R.K. Roy, K.R. Lee, J. Biomed. Mater. Res. B—Appl. Biomater. 83B (2007) 72. G. Dearnaley, J.H. Arps, Surf. Coat. Technol. 200 (2005) 2518. R. Hauert, Diamond Relat. Mater. 12 (2003) 583. M. Braic, M. Balaceanu, V. Braic, A. Vladescu, G. Pavelescu, M. Albulescu, Surf. Coat. Technol. 200 (2005) 1014. R. Hubler, A. Cozza, T.L. Marcondes, R.B. Souza, F.F. Fiori, Surf. Coat. Technol. 142– 144 (2001) 1078. Y.X. Leng, H. Sun, P. Yang, J.Y. Chen, J. Wang, G.J. Wan, N. Huang, X.B. Tian, L.P. Wang, P.K. Chu, Thin Solid Films 398–399 (2001) 471. A. Wisbey, P.J. Gregson, M. Tuke, Biomaterials 8 (1987) 477.
1605
[17] O. Knotek, F. Loffler, K. Weitkamp, Surf. Coat. Technol. 55 (1992) 536. [18] P.V. Kola, S. Daniels, D.C. Cameron, M.S.J. Hashmi, J. Mater. Process. Technol. 56 (1996) 422. [19] H. Behrndt, A. Lunk, Mater. Sci. Eng. A—Struct. Mater. Prop. Microstruc. Proc. 139 (1991) 58. [20] J. Zhao, L. Li, D.J. Li, H.Q. Gu, J. Adhes. Sci. Technol. 18 (2004) 1003. [21] A. Kamali, R. Farrar, P. Hatto, M. Stone, J. Fisher, Proc. Inst. Mech. Eng. Part J J. Eng. Tribol. 219 (2005) 41. [22] M. Hoseini, A. Jedenmalm, A. Boldizar, Wear 264 (2008) 958. [23] F.Z. Cui, D.J. Li, Surf. Coat. Technol. 131 (2000) 481. [24] M. Vojs, E. Zdravecka, M. Marton, P. Bohac, L. Franta, M. Vesely, Microelectron. J. 40 (2009) 650. [25] D. Sheeja, B.K. Tay, X. Shi, S.P. Lau, C. Daniel, S.M. Krishnan, L.N. Nung, Diamond Relat. Mater. 10 (2001) 1043. [26] D. Sheeja, B.K. Tay, S.P. Lau, L.N. Nung, Surf. Coat. Technol. 146–147 (2001) 410. [27] J.C. Avelar-Batista, E. Spain, G.G. Fuentes, A. Sola, R. Rodriguez, J. Housden, Surf. Coat. Technol. 201 (2006) 4335. [28] S.D.A. Lawes, M.E. Fitzpatrick, S.V. Hainsworth, J. Phys. D-Appl. Phys. 40 (2007) 5427. [29] L. Wang, X. Nie, J. Housden, E. Spain, J.C. Jiang, E.I. Meletis, A. Leyland, A. Matthews, Surf. Coat. Technol. 203 (2008) 816. [30] L. Wang, D.O. Northwood, X. Nie, J. Housden, E. Spain, A. Leyland, A. Mathews, J. Power Sources 195 (2010) 3814. [31] H.S. Khatak, B. Raj (Eds.), Corrosion of Austenitic Stainless Steels, Woodhead Publishing Limited, Cambridge, 2002, p. 43. [32] J.C. Kotz, P.M. Treichel, G.C. Weaver, Chemistry and chemical reactivity, Thomson Leaming Inc., Belmont, 2006, p. 975. [33] H. Cachet, C. Debiemme-Chouvy, C. Deslouis, A. Lagrini, V. Vivier, Surf. Interface Anal. 38 (2006) 719.