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Nanocrystalline Ni–W coatings on copper
Materials Science and Engineering B 176 (2011) 477–479
Contents lists available at ScienceDirect
Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb
Nanocrystalline Ni–W coatings on copper C.N. Panagopoulos ∗ , G.D. Plainakis, D.A. Lagaris Laboratory of Physical Metallurgy, National Technical University of Athens, Zografos, 15780, Athens, Greece
a r t i c l e
i n f o
Article history: Received 4 September 2009 Received in revised form 3 February 2010 Accepted 23 March 2010 Keywords: Nickel Tungsten Coating Adhesion
a b s t r a c t Nanocrystalline Ni–W coatings were produced on copper substrates with the aid of electrodeposition technique. The morphology, chemical composition and structure of the produced coatings were examined with the aid of scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The microhardness of alloy Ni–W coatings on copper substrate was also studied. The adhesion between the Ni–W coating, having W content 50 wt%, and the copper substrate, was also studied with a scratch testing apparatus. The scratch tests resulted in the coatings suffering an intensive brittle fracture and minor delamination. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Electrodeposited Ni–W alloy coatings are bright and exhibit high hardness and high thermal stability. Yamasaki et al. [1,2] prepared amorphous Ni–W coatings which, with increasing temperature of heat treatment, became nanocrystalline. Donten et al. [3] compared the Fe–Ni–W coatings to the Fe–W and Ni–W alloy coatings and they found that the introduction of iron in the Ni–W coatings eliminates the microcracks and reduces the tensile stress in the electrodeposited layers. Gileadi and co-workers [4–6], investigated the mechanism of the electrodeposited high tungsten content nickel alloys and reported the influence of the ammonia, the complex agent in the bath, the temperature, the current density on the current efficiency of the electrodeposition process. Cesiulis et al. [7] investigated the effect of the nickel concentration and the rate of deposition on the grain size of the nanocrystalline Ni–W coatings. Panagopoulos et al. [8] investigated the structure of Ni–P–W electrodeposited multilayer amorphous coatings on copper, with a grain size of about 5 nm. In the present work the microhardness of electrodeposited Ni–W coatings is given as a function of the grain size. Moreover, the adhesion between the nanocrystalline Ni–W coatings and the copper substrate have been studied and presented for the first time. 2. Experimental The substrate material used in this study was a commercial purity copper sheet. From this sheet, parallelepiped specimens
∗ Corresponding author. Tel.: +30 210 7722171; fax: +30 210 7722119. E-mail address: [email protected] (C.N. Panagopoulos). 0921-5107/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2010.03.058
of 5 cm × 2 cm × 0.1 cm dimensions were prepared. Prior to the electrodeposition, all copper substrate specimens were mechanically polished with SiC abrasive papers with increasing finishes i.e. decreasing roughness, cleaned with distilled water and activated by immersion in 10% (w/v) hydrochloric acid solution for 10 s and finally rinsed again with distilled water. The chemical composition of the plating bath is presented in Table 1. The other experimental electrodeposition parameters were: temperature 65 ◦ C, pH ≈ 7.5, intense agitation (300 rpm), current density 50, 100, 150, 200 mA/cm2 and deposition time 60 min. A two electrodes cell was used. A copper sheet with an exposed area of 1 cm2 was used as the cathode-working electrode. A platinum sheet with the same exposed area was used as anode, being placed at about 15 mm away from the cathode. The surface morphology of the produced Ni–W coatings was examined with the aid of a Jeol 6100 scanning electron microscope (SEM), which was connected with a Noran TS 5500 energy dispersive spectrometer (EDS) and an Image Pro Image Analysis System. Thickness was measured on the cross section of the Ni–W coated copper, using an optical microscope and with the aid of an image analysis program. The structure of the coating was investigated using a Siemens D 5000 X-ray diffractometer (XRD) with Cu K␣ radiation and a graphite monochromator. Microhardness testing was performed using a Shimadzu Vickers HMV 2000 indenter, imposing 0.15 N for 15 s. The adhesion strength between the Ni–W coatings and the copper substrate was studied with the aid of a CSEM Revetest scratch testing technique. The scratch tester was equipped with a Rockwell C conical diamond indenter, having a tip angle of 120◦ and a tip radius of 200 m. During the tests, an acoustic emission detector
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C.N. Panagopoulos et al. / Materials Science and Engineering B 176 (2011) 477–479
Table 1 Plating bath composition. Solution for electrodeposition
NiSO4 *7H2 O Na2 WO4 *2H2 O Na3 C6 H5 O7 *2H2 O NH4 Cl H3 BO3 NaBr
Agent
C (mol/L)
Property
Nickel sulfate heptahydrate Sodium tungstate dihydrate Trisodium citrate dihydrate Ammonium chloride Boric acid Sodium bromide
0.06 0.15 0.30 0.50 1.00 0.15
Ni source W source Complexer Efficiency Buffer Conductivity
Fig. 4. The microhardness of Ni–W coatings as a function of grain size.
using a scanning electron microscope. It should be noted that each experiment of this study was performed four times and the mean values are given in the graphs. 3. Results and discussion
Fig. 1. SEM micrograph of a Ni–W coating electrodeposited with ICD = 150 mA/cm2 , T = 65 ◦ C, t = 60 min.
Fig. 2. Thickness of the Ni–W alloy coating as a function of current density for deposition time 60 min and plating temperature 65 ◦ C.
recorded the signals from the alloy coating specimens. All scratch tests were conducted under increasing load, with a load rate of 10 N/mm. The minimum load was 0 and the maximum load was 100 N. The tracks from the adhesion experiments, were observed
Surface metallographic examination of the Ni–W alloy coatings shows a typical pattern with globular crystallites (Fig. 1). EDS technique shows that the mean composition of the alloy coating is: Ni (50 wt%)–W (50 wt%). Taking into account the composition of the produced Ni–W coatings and examining the phase diagram of Ni–W system [9], it can be suggested that two phases co-exist in the coatings: solid solution of Ni with W and an intermetallic compound NiW. Thickness values of the produced Ni–W alloy coatings show to be dependent on the current density, time and temperature during the electrodeposition process. A typical coating thickness dependence on applied current density is given in Fig. 2. Similar relationship was also found for the coatings thickness dependence on the time and temperature. Fig. 3 shows the X-ray diffraction peaks from two electrodeposited Ni–W coatings. These diffraction peaks are indicative of nanocrystalline structure Ni–W coatings, as correspond to the solid solution of Ni (1 1 1) with W. By using the Debye–Scherrer equation the grain size of the coatings was found to be approximately: (a) 10 nm, (b) 15 nm. The fact that only a few experimental points are obtained in the present analysis, renders insecure the deduction of a positive correlation between the resulting grain size and the working current. More experimental data points are needed to demonstrate the relation between these two quantities. Fig. 4 shows the microhardness of the examined nanocrystalline Ni–W coatings versus the grain size. For grain size above the value of 10 nm the results are in full agreement with the Hall–Petch effect.
Fig. 3. (a) The XRD pattern of an electrodeposited Ni–W coating on copper with ICD = 100 mA/cm2 , T = 65 ◦ C, t = 60 min. (b) The XRD pattern of an electrodeposited Ni–W coating on copper with ICD = 200 mA/cm2 , T = 65 ◦ C, t = 60 min.
C.N. Panagopoulos et al. / Materials Science and Engineering B 176 (2011) 477–479
479
4. Conclusions From the previous experimental investigation the following deductions could be made: • Ni–W coatings were electrodeposited on copper substrate. The produced coatings were uniform in thickness and nanocrystalline with some very few cracks. • The tungsten wt% content in the alloy was found to be approximately 50. • The microhardness of the Ni–W coatings, was found to be in the range of 460–740 HVN. • The scratch test applied in the Ni–W coatings sowed that the coatings suffer brittle fracture and minor delamination. Fig. 5. SEM micrograph indicating enlarged area of the scar of a Ni–W coating at a distance of about 2 mm (Load 15–20 N) from the start of the indentation.
References
This effect support the opinion for the theoretical and experimental points of view that the decrease of the grain size of metallic materials leads to the increase of the microhardness of these materials [10]. Fig. 5 shows a part of scratch scar of a Ni–W coating at a distance of two mm from the start of the indentation. It can be observed that the coating scar contains several brittle cracks perpendicular to the direction of the indentation. In the same figure, a small degree of coating delamination can be observed. From the early stages of scratch test, the coating suffers intensive brittle fracture and minor delamination.
[1] T. Yamasaki, P. Schlossmacher, K. Ehrlich, Y. Ogino, Nanostruct. Mater. 10 (1998) 375. [2] T. Yamasaki, Scripta Mater. 44 (2001) 1497–1502. [3] M. Donten, H. Cesiulis, Z. Stojek, Electrochim. Acta 45 (2000) 3389–3396. [4] L. Zhu, O. Younes, N. Ashkenasy, Y. Shacham-Diamand, E. Gileadi, J. Appl. Surf. Sci. 200 (2002) 1. [5] O. Younes, E. Gileadi, J. Electrochem. Soc. 149 (2002) C100. [6] O. Younes-Metzler, L. Zhu, E. Gileadi, Electrochim. Acta 48 (2003) 2551–2562. [7] H. Cesiulis, A. Baltutiene, M. Donten, M.L. Donten, Z. Stojek, Solid State Electrochem. 6 (2002) 237–244. [8] C.N. Panagopoulos, V.D. Papachristos, U. Wahlstrom, P. Leisner, L.W. Christoffersen, Scripta Mater. 43 (2000) 677–683. [9] M. Hansen, Constitution of Binary Alloys, McGraw-Hill, New York, 1958, p. 1058. [10] C. Schuh, T.G. Nieh, H. Iwasaki, Acta Mater. 51 (2003) 431–443.
Contents lists available at ScienceDirect
Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb
Nanocrystalline Ni–W coatings on copper C.N. Panagopoulos ∗ , G.D. Plainakis, D.A. Lagaris Laboratory of Physical Metallurgy, National Technical University of Athens, Zografos, 15780, Athens, Greece
a r t i c l e
i n f o
Article history: Received 4 September 2009 Received in revised form 3 February 2010 Accepted 23 March 2010 Keywords: Nickel Tungsten Coating Adhesion
a b s t r a c t Nanocrystalline Ni–W coatings were produced on copper substrates with the aid of electrodeposition technique. The morphology, chemical composition and structure of the produced coatings were examined with the aid of scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The microhardness of alloy Ni–W coatings on copper substrate was also studied. The adhesion between the Ni–W coating, having W content 50 wt%, and the copper substrate, was also studied with a scratch testing apparatus. The scratch tests resulted in the coatings suffering an intensive brittle fracture and minor delamination. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Electrodeposited Ni–W alloy coatings are bright and exhibit high hardness and high thermal stability. Yamasaki et al. [1,2] prepared amorphous Ni–W coatings which, with increasing temperature of heat treatment, became nanocrystalline. Donten et al. [3] compared the Fe–Ni–W coatings to the Fe–W and Ni–W alloy coatings and they found that the introduction of iron in the Ni–W coatings eliminates the microcracks and reduces the tensile stress in the electrodeposited layers. Gileadi and co-workers [4–6], investigated the mechanism of the electrodeposited high tungsten content nickel alloys and reported the influence of the ammonia, the complex agent in the bath, the temperature, the current density on the current efficiency of the electrodeposition process. Cesiulis et al. [7] investigated the effect of the nickel concentration and the rate of deposition on the grain size of the nanocrystalline Ni–W coatings. Panagopoulos et al. [8] investigated the structure of Ni–P–W electrodeposited multilayer amorphous coatings on copper, with a grain size of about 5 nm. In the present work the microhardness of electrodeposited Ni–W coatings is given as a function of the grain size. Moreover, the adhesion between the nanocrystalline Ni–W coatings and the copper substrate have been studied and presented for the first time. 2. Experimental The substrate material used in this study was a commercial purity copper sheet. From this sheet, parallelepiped specimens
∗ Corresponding author. Tel.: +30 210 7722171; fax: +30 210 7722119. E-mail address: [email protected] (C.N. Panagopoulos). 0921-5107/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2010.03.058
of 5 cm × 2 cm × 0.1 cm dimensions were prepared. Prior to the electrodeposition, all copper substrate specimens were mechanically polished with SiC abrasive papers with increasing finishes i.e. decreasing roughness, cleaned with distilled water and activated by immersion in 10% (w/v) hydrochloric acid solution for 10 s and finally rinsed again with distilled water. The chemical composition of the plating bath is presented in Table 1. The other experimental electrodeposition parameters were: temperature 65 ◦ C, pH ≈ 7.5, intense agitation (300 rpm), current density 50, 100, 150, 200 mA/cm2 and deposition time 60 min. A two electrodes cell was used. A copper sheet with an exposed area of 1 cm2 was used as the cathode-working electrode. A platinum sheet with the same exposed area was used as anode, being placed at about 15 mm away from the cathode. The surface morphology of the produced Ni–W coatings was examined with the aid of a Jeol 6100 scanning electron microscope (SEM), which was connected with a Noran TS 5500 energy dispersive spectrometer (EDS) and an Image Pro Image Analysis System. Thickness was measured on the cross section of the Ni–W coated copper, using an optical microscope and with the aid of an image analysis program. The structure of the coating was investigated using a Siemens D 5000 X-ray diffractometer (XRD) with Cu K␣ radiation and a graphite monochromator. Microhardness testing was performed using a Shimadzu Vickers HMV 2000 indenter, imposing 0.15 N for 15 s. The adhesion strength between the Ni–W coatings and the copper substrate was studied with the aid of a CSEM Revetest scratch testing technique. The scratch tester was equipped with a Rockwell C conical diamond indenter, having a tip angle of 120◦ and a tip radius of 200 m. During the tests, an acoustic emission detector
478
C.N. Panagopoulos et al. / Materials Science and Engineering B 176 (2011) 477–479
Table 1 Plating bath composition. Solution for electrodeposition
NiSO4 *7H2 O Na2 WO4 *2H2 O Na3 C6 H5 O7 *2H2 O NH4 Cl H3 BO3 NaBr
Agent
C (mol/L)
Property
Nickel sulfate heptahydrate Sodium tungstate dihydrate Trisodium citrate dihydrate Ammonium chloride Boric acid Sodium bromide
0.06 0.15 0.30 0.50 1.00 0.15
Ni source W source Complexer Efficiency Buffer Conductivity
Fig. 4. The microhardness of Ni–W coatings as a function of grain size.
using a scanning electron microscope. It should be noted that each experiment of this study was performed four times and the mean values are given in the graphs. 3. Results and discussion
Fig. 1. SEM micrograph of a Ni–W coating electrodeposited with ICD = 150 mA/cm2 , T = 65 ◦ C, t = 60 min.
Fig. 2. Thickness of the Ni–W alloy coating as a function of current density for deposition time 60 min and plating temperature 65 ◦ C.
recorded the signals from the alloy coating specimens. All scratch tests were conducted under increasing load, with a load rate of 10 N/mm. The minimum load was 0 and the maximum load was 100 N. The tracks from the adhesion experiments, were observed
Surface metallographic examination of the Ni–W alloy coatings shows a typical pattern with globular crystallites (Fig. 1). EDS technique shows that the mean composition of the alloy coating is: Ni (50 wt%)–W (50 wt%). Taking into account the composition of the produced Ni–W coatings and examining the phase diagram of Ni–W system [9], it can be suggested that two phases co-exist in the coatings: solid solution of Ni with W and an intermetallic compound NiW. Thickness values of the produced Ni–W alloy coatings show to be dependent on the current density, time and temperature during the electrodeposition process. A typical coating thickness dependence on applied current density is given in Fig. 2. Similar relationship was also found for the coatings thickness dependence on the time and temperature. Fig. 3 shows the X-ray diffraction peaks from two electrodeposited Ni–W coatings. These diffraction peaks are indicative of nanocrystalline structure Ni–W coatings, as correspond to the solid solution of Ni (1 1 1) with W. By using the Debye–Scherrer equation the grain size of the coatings was found to be approximately: (a) 10 nm, (b) 15 nm. The fact that only a few experimental points are obtained in the present analysis, renders insecure the deduction of a positive correlation between the resulting grain size and the working current. More experimental data points are needed to demonstrate the relation between these two quantities. Fig. 4 shows the microhardness of the examined nanocrystalline Ni–W coatings versus the grain size. For grain size above the value of 10 nm the results are in full agreement with the Hall–Petch effect.
Fig. 3. (a) The XRD pattern of an electrodeposited Ni–W coating on copper with ICD = 100 mA/cm2 , T = 65 ◦ C, t = 60 min. (b) The XRD pattern of an electrodeposited Ni–W coating on copper with ICD = 200 mA/cm2 , T = 65 ◦ C, t = 60 min.
C.N. Panagopoulos et al. / Materials Science and Engineering B 176 (2011) 477–479
479
4. Conclusions From the previous experimental investigation the following deductions could be made: • Ni–W coatings were electrodeposited on copper substrate. The produced coatings were uniform in thickness and nanocrystalline with some very few cracks. • The tungsten wt% content in the alloy was found to be approximately 50. • The microhardness of the Ni–W coatings, was found to be in the range of 460–740 HVN. • The scratch test applied in the Ni–W coatings sowed that the coatings suffer brittle fracture and minor delamination. Fig. 5. SEM micrograph indicating enlarged area of the scar of a Ni–W coating at a distance of about 2 mm (Load 15–20 N) from the start of the indentation.
References
This effect support the opinion for the theoretical and experimental points of view that the decrease of the grain size of metallic materials leads to the increase of the microhardness of these materials [10]. Fig. 5 shows a part of scratch scar of a Ni–W coating at a distance of two mm from the start of the indentation. It can be observed that the coating scar contains several brittle cracks perpendicular to the direction of the indentation. In the same figure, a small degree of coating delamination can be observed. From the early stages of scratch test, the coating suffers intensive brittle fracture and minor delamination.
[1] T. Yamasaki, P. Schlossmacher, K. Ehrlich, Y. Ogino, Nanostruct. Mater. 10 (1998) 375. [2] T. Yamasaki, Scripta Mater. 44 (2001) 1497–1502. [3] M. Donten, H. Cesiulis, Z. Stojek, Electrochim. Acta 45 (2000) 3389–3396. [4] L. Zhu, O. Younes, N. Ashkenasy, Y. Shacham-Diamand, E. Gileadi, J. Appl. Surf. Sci. 200 (2002) 1. [5] O. Younes, E. Gileadi, J. Electrochem. Soc. 149 (2002) C100. [6] O. Younes-Metzler, L. Zhu, E. Gileadi, Electrochim. Acta 48 (2003) 2551–2562. [7] H. Cesiulis, A. Baltutiene, M. Donten, M.L. Donten, Z. Stojek, Solid State Electrochem. 6 (2002) 237–244. [8] C.N. Panagopoulos, V.D. Papachristos, U. Wahlstrom, P. Leisner, L.W. Christoffersen, Scripta Mater. 43 (2000) 677–683. [9] M. Hansen, Constitution of Binary Alloys, McGraw-Hill, New York, 1958, p. 1058. [10] C. Schuh, T.G. Nieh, H. Iwasaki, Acta Mater. 51 (2003) 431–443.