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Characteristics of Ni–P alloy electrodeposited from a sulfamate bath
Surface and Coatings Technology 176 (2004) 135–140
Characteristics of Ni–P alloy electrodeposited from a sulfamate bath Moo Hong Seoa,*, Joung Soo Kimb, Woon Suk Hwangc, Dong Jin Kimb, Seong Sik Hwangb, Byung Sun Chuna a
Department of Metallurgy, Chungnam National University, Taejon, South Korea b Korea Atomic Energy Research Institute, Taejeon, South Korea c Department of Metallurgy, Inha University, Inchon, South Korea Received 28 June 2002; accepted in revised form 24 March 2003
Abstract The effect of H3PO3 concentration on Ni–P electrodeposition from sulfamate bath and the material properties of the deposit with heat treatment were investigated. With increasing H3 PO3 concentration in the bath, the phosphorus content in the deposit increased, while the current efficiency slowly decreased and stress in the deposit increased. This result seems to be related to the increase of hydrogen evolution and absorption reactions accompanied by the increase of phosphorus content in the deposit. The size of the grains and the precipitates in Ni–1.52 wt.% P deposit rapidly increased during heat treatment at temperatures equal to or higher than approximately 490 8C, fairly consistent with the results of Vickers hardness tests. The microstructural and mechanical property variation of the deposits with heat treatment were explained by precipitation of Ni3 P at 310 8C and recrystallization at 575 8C with the supplemental help of DSC (differential scanning calorimetry) results. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Electrodeposition; Ni–P alloy; Sulfamate; Current efficiency; Residual stress
1. Introduction Ni–P alloy obtained by electrolytic deposition has been highlighted due to its good physical and chemical properties, such as high corrosion resistance, good magnetic and thermal properties, etc. w1–4x. However, most research on the electrodeposition of Ni–P alloys have been restricted to Watts or sulfate baths w5–8x rather than a sulfamate bath, in spite of its several advantages, such as, high solubility in an aqueous solution, enabling high current density applications and excellent stability for pH values ranging from 1 to 4 and for temperatures up to 60 8C w9,10x. In addition, the stress values of electrodeposits made from sulfamate, sulfate and Watts nickel baths without the addition of an agent are reported to be approximately 30, 180 and 250 MPa, respectively w11x. Owing to the advantages of a sulfamate bath, a concentrated nickel sulfamate solution without organic *Corresponding author. Korea Atomic Energy Research Institute, Nuclear Material Technology Development Team, P.O. Box 105, Dukjin-dong, Yusong-gu, Taejeon, Republic of Korea. Tel.: q82-42868-2759; fax: q82-42-868-8549. E-mail address: [email protected] (M.H. Seo).
stress reducers has been recommended for thick deposition. Nevertheless, most research on Ni electrodeposition from the sulfamate bath was focused on pure Ni rather than Ni alloy w12–15x. The main objective of this work is to develop a Ni– P electrodeposition technology from a sulfamate bath for application to the repair of fault steam generator tubing in nuclear power plants w16,17x. The electrodeposits need to have high process efficiency and superior material properties, especially residual stress of the deposit. In this preliminary study, the effect of H3PO3 concentration on Ni–P electrodeposition from the sulfamate bath and the properties of the deposited layer with heat treatment were investigated. The results of this study show that current efficiency and residual stress of the deposits obtained from a sulfamate bath are higher and lower, respectively, than those from the sulfate bath. These results are unique, because no such data have yet been reported. Moreover, previous research on the microstructure of Ni–P alloys obtained by electroless and electrolytic deposition are mainly focused on the structural change from the amorphous phase to the crystalline one at a relatively high phosphorus content
0257-8972/04/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972Ž03.00661-3
M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
136 Table 1 Bath compositions Sulfamate bath Ni(SO3NH2)2 H3BO3 H3PO3
Sulfate bath 1.39 M 0.65 M 0–0.18 M
NiSO4 H3BO3 H3PO3
1.43 M 0.65 M 0–0.18 M
over several weight percent w18–21x, and the effects of various anions in electrodeposited nickel on the submicrostructure of the deposits w22x. This study on Ni–1.5 wt.% P electrodeposits from a sulfamate bath shows that the microstructure of the deposit consists of dislocation cells with grains surrounded by highly dense dislocations, and the concentration profile of the cross section in the deposit with the thickness is uniform as confirmed by EPMA rather than changed regularly as reported by Despic and Jovic w23x. This is the first report showing the needle shaped precipitation of Ni3P in the microstructure of the deposited layer. 2. Experimental 2.1. Process Ni sulfamate or sulfate as a Ni source, phosphorus acid as a P source, Pt plated Ti with a surface area of 5=6 cm2 as an anode and alloy 600 plate with a surface area of 2=2 cm2 as a cathode were used in Ni–P alloy electrodeposition, respectively. Table 1 shows bath compositions used in this study. Conventional sulfamate bath contains small content of nickel chloride, increasing internal stress in the deposits, but it was not used in this experiment. Ni–P alloy electrodepositions were performed in sulfamate and sulfate baths with the same electrolysis condition as follows: temperature 50 8C, current density 10 Aydm2, pH 1, deposition time 60 min and agitation speed 70 rpm using a stirrer bar. pH was adjusted by sulfamic and sulfuric acids in sulfamate and sulfate baths, respectively. The cathode was polished to 噛1500 emery paper and ultrasonically cleaned in alkaline solution, followed by activation treatment in a 10 wt.% H2SO4 solution for 10 s at 60 8C. The deposit could be separated easily from the substrate due to the weak adhesion between the deposit and the oxide layer already existing in the surface of substrate.
(electron probe micro analyzer, Model SX-50 (CAMECA)). The deposit from sulfamate bath was heat-treated at a temperature in the range of 20–850 8C for 1 h under vacuum of 10y3 torr and was cooled in air. TEM microstructure of the specimen was investigated using Jeol 2000FX equipped with Oxford Link (Model ISIS5947) EDX. Thin foil was prepared by jet polishing using 60% methanolq35% n-butyl alcoholq5% perchloric acid solution at y30 8C, and DC 20 V. A carbon replica was manufactured as follows. Firstly, the sample was electrochemically etched into the 98% methanolq 2% hydrochloric acid solution at DC 6 V for 15 s. Secondly, the etched sample was coated by carbon, and thirdly the carbon coated layer was separated from the substrate. The hardness was measured with a load of 100 gf using the Vickers Hardness Tester (MXT-CX (Matssuzawa)). Thermal analysis was performed by DSC-50 (Matssuzawa) under the condition of Ar 30 mlymin and heating rate 20 8Cymin. 3. Results and discussion 3.1. Phosphorus content Fig. 1 shows variation of phosphorus content in the deposit with H3PO3 concentration in electrolytic solutions. Phosphorus content in both deposits from sulfamate and sulfate baths increased with increasing H3PO3 concentration, consistent with the results reported elsewhere w24,25x. For deposition from sulfamate bath, phosphorus content in the deposit increased from 0.2 to 0.9 wt.% P with increasing H3PO3 concentration from 0.007 to 0.018 M. For deposition from sulfate bath, the phosphorus content in the deposit was higher than that in the deposit from sulfamate bath. From the results of alloy compositions in the deposit, it was found that phosphorus was more readily incorporated during the electrodeposition from the sulfate bath than the sulfamate bath.
2.2. Analysis Alloy composition analysis of the deposit was performed using ICP analyzer (Model JY80C (Jobin Yvon)). Stress in the deposit was measured in-situ using a spiral contractometer (QCI). Line analysis of alloy composition with thickness from the interface of the depositysubstrate to surface of the deposit at cross section of the deposit was performed using EPMA
Fig. 1. Phosphorus content in the deposit with H3PO3 concentration from sulfamate and sulfate baths.
M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
Fig. 2. Current efficiency with H3PO3 concentration from sulfamate and sulfate baths.
3.2. Current efficiency Cathodic current efficiencies of Ni–P deposition in sulfamate and sulfate baths are shown in Fig. 2. The current efficiency could be calculated from Faraday’s law using the measured weight change and the known composition of the deposit. Current efficiencies decreased with the increasing H3PO3 concentration in the baths, irrespective of the bath. It has been reported that current efficiencies decreased with increasing H3PO3 concentration in chloride and citrate baths, consistent with the results of this work w26,27x. The current efficiency in sulfamate baths was higher than that in sulfate baths and the difference in current efficiency between two baths increased with increasing H3PO3 concentration. Vitkova et al. w28x reported that the decrease of the current efficiency with increasing NaH2PO2 concentration during Ni–Fe–P alloy electrodeposition was caused by a change of hydrogen overvoltage upon the alloys having various compositions. Karayannis et al. w29x reported that the current efficiency in a chloride bath was higher than that in a sulfate bath, while the sulfate ion in the sulfate bath affects the hydrogen evolution more strongly than the chloride ion in the chloride bath. Accordingly, it can be expected that H3PO3 concentration in the baths affected hydrogen over-voltage by change of the Ni–P alloy composition in the deposit during electrodeposition and the sulfate anion rather than sulfamate anion can assist effectively side reaction such as the hydrogen evolution.
137
sulfamate bath showed about a half lower stress than that from sulfate bath. Stress in the deposit originates from the co-deposition of hydrogen and metal during electrodeposition w30,31x. Burchardt w32x reported that the rate of the hydrogen evolution reaction was expressed as a function of the phosphorus content in the NiPx alloy (-6.7 wt.% P) and hydrogen adsorption in the deposit was proportional to hydrogen evolution during electrodeposition from a sulfate bath containing NaH2PO2. Under these circumstances, it can be presumed that hydrogen absorption and evolution reactions increased leading to an increase of the stress in the deposit as the H3PO3 concentration in the baths increased, i.e. the phosphorus content in the deposits increased. Consistently, the stress in the deposit from the sulfate bath, where the phosphorus could be more readily incorporated was higher than that from the sulfamate bath. 3.4. Cross-section Fig. 4a is an optical micrograph for cross section of the deposit showing laminar structure. Numerous laminar lines were observed over the whole deposit. Laminar lines in the overdeposited region are shown in Fig. 4b at the edge of the deposit. These laminar lines seem to be formed along the equipotential line during electrodeposition. Dini w33x and Chassaing et al. w34x reported that laminar structure was shown in the alloy such as electrodeposited Au–Cu, Co–P, Co–W and Ni–Mo. Despic and Jovic w23x claimed that laminar structure was formed by repeating the process in which the partial current of one species increases as the partial current of the other species decreases during the electrodeposition of Cu–Pb binary alloy applying the direct current and was thereby composed of multilayers with two kinds of compositions in binary alloy electrodeposition system. Fig. 5 is the result of a line analysis by EPMA. Unlike the model proposed by Despic and Jovic w23x, a variation in the composition of Ni–P alloy with thick-
3.3. Stress Fig. 3 shows stress in the deposit with H3PO3 concentration in the sulfamate and sulfate baths. Stress in the deposit linearly increased from 45.9 to 74.8 MPa and from 106 to 144.8 MPa, respectively, as the H3PO3 concentration in the sulfamate and sulfate baths increased. The measured stress for the deposit from
Fig. 3. Stress in the deposit with H3PO3 concentration from sulfamate and sulfate baths.
M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
138
Fig. 4. Optical photographs showing cross-section (a) in the center and (b) at the edge of the Ni–P electrodeposit.
ness from interface of the depositysubstrate to the surface of the deposit was so small that it could be ignored indicating the composition of the alloy with a uniform thickness. Thus, nickel must be involved in electrodeposition of Ni–P alloys, because phosphorus cannot be directly electrodeposited in aqueous solution w35x. 3.5. Microstructure Fig. 6 shows the microstructure of Ni–1.52 wt.% P deposit from sulfamate bath with heat treatment temperature in the range of 20–850 8C for 1 h. Fig. 7 shows the mean size of grain and precipitate shown in Fig. 6. The deposit had dislocation cell structure with grain surrounded by highly dense dislocations as shown in Fig. 6a. Twins were not shown in this study as observed by others w36x. The mean size of grains at 20 8C was 123 nm. After heat treatment at 343 8C, Ni3P precipitates (identified by EDX and electron diffractions) appeared mainly at grain boundary and only a few precipitates smaller in size were observed in the grain interior,
Fig. 5. Depth profiles of Ni and P concentrations obtained from EPMA result of the electrodeposited Ni–P alloy.
Fig. 6. TEM micrographs with heat treatment at temperature of (a) 20; (b) 343; (c), (d) 490; (e), (f) 580; (g) 700; (h) 850 8C, respectively. Fig. 6 (e) micrograph was prepared by carbon replica method.
M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
139
increasing heat treatment temperature. Precipitates along grain boundary and in grains resembled polyhedral and circle shapes, respectively, as shown in Fig. 6h. 3.6. Hardness
Fig. 7. The mean size of the grain and precipitate as a function of heat treatment temperature in the range of 20–850 8C.
whereas the mean size of grain was nearly invariant compared to the grain size at 20 8C as shown in Fig. 6b. The retardation of grain growth during heat treatment at 343 8C seems to be due to a Zener drag effect w37x. Rapid grain growth at a temperature of 490 8C occurred and hence the mean size of grain at 490 8C reached 620 nm as shown in Fig. 6c and Fig. 7. Rapid grain growth was concerned with the coarsening of Ni3P precipitates leading to the reduction in the grain boundary pinning force. After heat treatment at 490 8C, needle-like Ni3P precipitates (identified by EDX) were observed as shown in Fig. 6d unlike the round shaped precipitates of Fig. 6c. According to the analysis of carbon replicas as shown Fig. 6e, it was found that the needle type precipitates were accumulated over the deposit nonuniformly and their sizes were much smaller than those of the round type. Therefore, it can be presumed that Ni3P precipitate of needle type precipitated after precipitation of Ni3P precipitates of the round type is already shown above. The deposit was recrystallized after heat treatment at 580 8C for 1 h as shown in Fig. 6f. Dubois et al. w38x reported that temperature of recrystallization of high pure Ni and commercial Ni was 230 and 600 8C, respectively. The precipitates formed at grain boundary could be used as the dislocation accumulation, nucleation and recrystallization sites for the highly cold worked materials, which lowers the activation energies for the transformations w39,40x. Therefore, it seems that the Ni– P electrodeposit could be recrystallized at a lower temperature than that of commercial Ni due to the precipitates existing along grain boundary. Ni3P precipitates within the grain interior increased in size and density during heat treatment at 700 8C as shown in Fig. 6g, compared with the results at 343 8C of Fig. 6b. This seems to be due to the increase of diffusion rate of phosphorus in grain interiors with
Fig. 8 shows the microhardness of Ni–1.52 wt.% P deposit with heat treatment temperature in the range from 20–850 8C for 1 h. Microhardness of the deposit increased from Hv450 to Hv550 until the heat treatment temperature increased to approximately 450 8C. However, microhardness decreased to approximately Hv200 after heat treatment at the higher temperature than 450 8C as the heat treatment temperature increased. Considering the microstructural and microhardness results, it is conceivable to think that the amount of Ni3P precipitate increased and hence the microhardness increased with increasing heat treatment temperature to approximately 450 8C. However, the rapid decrease of microhardness caused by the precipitate coarsening, grain growth and recrystallization appeared as the heat treatment temperature increased to a higher temperature. Muscra et al. w41x reported that hardness of the electro-
Fig. 8. Plot of hardness against heat treatment temperature for 1 h.
Fig. 9. DSC result of Ni-1.52 wt.% P deposit.
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M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
sleeve material with time under isothermal aging at temperature of 600 8C rapidly decreased after 10 min. 3.7. Thermal analysis Fig. 9 shows the result of DSC analysis on a Ni– 1.52 wt.% P deposit. Two exothermic peaks at approximately 310 and 575 8C were observed. The first one at approximately 310 8C seems to be concerned with formation of Ni3P precipitates and the second one at approximately 575 8C is due to recrystallization, respectively, as demonstrated in Fig. 6. 4. Conclusions The effect of H3PO3 concentration on Ni–P electrodeposition from sulfamate and sulfate baths and material properties of the deposit from sulfamate bath with heat treatment in the range of 20–850 8C for 1 h were investigated: 1. As the phosphorus content in the deposit increased, current efficiency slowly decreased, but the stress in the deposit increased. This occurrence appeared more clearly from the sulfate bath where the phosphorus can be readily incorporated than the sulfamate bath. This was explained by the increase of hydrogen evolution and absorption reactions induced by the increase of phosphorus content in the deposit. 2. The size of the grain and precipitate in Ni–1.52 wt.% P deposit from sulfamate bath rapidly increased during heat treatment at temperature above 490 8C, leading to the decrease of microhardness. The microstructural and mechanical properties of the deposit from sulfamate bath with heat treatment were explained by precipitation of Ni3P at 310 8C and recrystallization at 575 8C with the supplemental help of DSC results. References w1x M.G. Fontana, Corrosion Engineering, 3, B and Jo Enterprise, Singapore, 1986, 243. w2x J.E. Williams, C. Davison, J. Electrochem. Soc. 137 (1990) 3260. w3x D. Osmola, P. Nolan, U. Erb, G. Palumbo, K.T. Aust, Phys. Stat. Sol. (a) 131 (1992) 569. w4x A. Robertson, U. Erb, G. Palumbo, Nanostruct. Mater. 12 (1999) 1035. w5x A. Brenner, Electrodeposition of Alloys II, Academic Press, New York, 1963. w6x K. Masui, S. Maruno, T. Yamada, J. Surf. Finish. Soc. Jpn. 41 (11) (1977) 1130. w7x P. Peeters, G. Hoorn, T. Daenen, A. Kurowski, G. Staikov, Electrochim. Acta 47 (2001) 161.
w8x C.C. Hu, A. Bai, Surf. Coat. Technol. 137 (2001) 181. w9x S.A. Watson, Addition to Sulfamate Nickel Solutions, NiDI Technical Series (1989) Nr.10053. w10x H. Zhang, S.M. Park, J. Appl. Electrochem. 24 (1994) 1182. w11x D. Baudrand, Met. Finish. 94 (7) (1996) 15. w12x B.B. Knapp, Plating 58 (1971) 1187. w13x F. Ebrahimi, G.R. Bourne, M.S. Kelly, T.E. Matthew, Nanostruct. Mater. 11 (3) (1999) 343. w14x G.A. DiBari, Met. Finish. 97 (1) (1999) 276. w15x Chiba, T. Gotou, K. Kobayashi, W.C. Wu, Met. Finish. 98 (9) (2000) 66. w16x F. Gonzalez, A.M. Brennenstuhl, G. Palumbo, U. Erb, P.C. Lichtenberger, Mater. Sci. Forum 225–227 (1996) 831. w17x A. Robertson, U. Erb, G. Palumbo, Nanostruct. Mater. 12 (1999) 1035. w18x B.G. Bagley, D. Turnbull, Acta Metall. 18 (1970) 857. w19x M.W. Mahoney, P.J. Dynes, Scr. Metall. 19 (1985) 539. w20x E. Bredael, B. Blanpain, J.P. Celis, J.R. Roos, J. Electrochem. Soc. 141 (1) (1994) 294. w21x K.G. Keong, W. Sha, S. Malinov, J. Mater. Sci. 37 (20) (2002) 4445. w22x V. Landa, M. Cermak, J. Vitek, Surf. Technol. 8 (4) (1979) 363. w23x A.R. Despic, V.D. Jovic, Modern Aspects of Electrochemistry, 27, Plenum Press, New York, 1995, p. 183. w24x K. Kuruma, K. Yamada, K. Sato, H. Kagechika, J. Surf. Finish. Soc. Jpn. 42 (10) (1991) 1013. w25x G.W. Marshall, D.B. Lewis, D. Clayton, K. Blake, B. Dodds, Surf. Coat. Technol. 96 (1997) 353. w26x K. Masui, T. Nomura, S. Kwon, D.Y. Chang, J. Surf. Finish. Soc. Jpn. 43 (3) (1992) 195. w27x T. Morikawa, T. Nakade, M. Yokoi, Y. Fukumoto, C. Iwakura, Electrochim. Acta 42 (1) (1997) 115. w28x S. Vitkova, Y. Gancheva, G. Raichevsky, Galvanotech Symp. 7 (1985) 381, (Vortr) 7th. w29x H.S. Karayannis, G. Patermarakis, Electrochim. Acta 40 (9) (1995) 1079. w30x I. Paseka, Electrochim. Acta 47 (2001) 921. w31x M. Ya. Popereka, Internal Stresses in Electrolytically Deposited Metals, transl. from Russian, Indian Nation Scientific Documentation Center, New Delhi, Nation Bureau of Standards and the Nation Science Foundation, Washington, DC (1970). w32x T. Burchardt, Int. J. Hydrogen Energy 26 (2001) 1193. w33x J.W. Dini, Electrodeposition, Noyes Publications, New Jersey, 1992, p. 145. w34x E. Chassaing, K.V. Quang, M.E. Baumgartner, M. Funk, C.J. Raub, Plating Surf. Finish. 1 (August 1990) 60. w35x T. Burchardt, Int. J. Hydrogen Energy 27 (2002) 323. w36x S.C. Mehta, D.A. Smith, U. Erb, Mater. Sci. Eng. A204 (1995) 227. w37x K. Boylan, D. Ostrander, U. Erb, G. Palumbo, K.T. Aust, Scr. Metall. et Materialia 25 (1991) 2711. w38x B. Dubois, A. Wache, C.R. Acad. Sci., Paris 256 (1963) 1302. w39x W.C. Leslie, J.T. Michalak, F.W. Aul, Iron and its Dilute Solid Solutions, Interscience, New York, 1963, p. 119. w40x R.W. Chan, Recrystallization, Grain Growth and Textures, Papers presented at a Seminar of the American Society for Metals, October, 1965, p. 116. w41x J. Muscra, ARGONNE National Laboratory Report, August, 1999.
Characteristics of Ni–P alloy electrodeposited from a sulfamate bath Moo Hong Seoa,*, Joung Soo Kimb, Woon Suk Hwangc, Dong Jin Kimb, Seong Sik Hwangb, Byung Sun Chuna a
Department of Metallurgy, Chungnam National University, Taejon, South Korea b Korea Atomic Energy Research Institute, Taejeon, South Korea c Department of Metallurgy, Inha University, Inchon, South Korea Received 28 June 2002; accepted in revised form 24 March 2003
Abstract The effect of H3PO3 concentration on Ni–P electrodeposition from sulfamate bath and the material properties of the deposit with heat treatment were investigated. With increasing H3 PO3 concentration in the bath, the phosphorus content in the deposit increased, while the current efficiency slowly decreased and stress in the deposit increased. This result seems to be related to the increase of hydrogen evolution and absorption reactions accompanied by the increase of phosphorus content in the deposit. The size of the grains and the precipitates in Ni–1.52 wt.% P deposit rapidly increased during heat treatment at temperatures equal to or higher than approximately 490 8C, fairly consistent with the results of Vickers hardness tests. The microstructural and mechanical property variation of the deposits with heat treatment were explained by precipitation of Ni3 P at 310 8C and recrystallization at 575 8C with the supplemental help of DSC (differential scanning calorimetry) results. 䊚 2003 Elsevier Science B.V. All rights reserved. Keywords: Electrodeposition; Ni–P alloy; Sulfamate; Current efficiency; Residual stress
1. Introduction Ni–P alloy obtained by electrolytic deposition has been highlighted due to its good physical and chemical properties, such as high corrosion resistance, good magnetic and thermal properties, etc. w1–4x. However, most research on the electrodeposition of Ni–P alloys have been restricted to Watts or sulfate baths w5–8x rather than a sulfamate bath, in spite of its several advantages, such as, high solubility in an aqueous solution, enabling high current density applications and excellent stability for pH values ranging from 1 to 4 and for temperatures up to 60 8C w9,10x. In addition, the stress values of electrodeposits made from sulfamate, sulfate and Watts nickel baths without the addition of an agent are reported to be approximately 30, 180 and 250 MPa, respectively w11x. Owing to the advantages of a sulfamate bath, a concentrated nickel sulfamate solution without organic *Corresponding author. Korea Atomic Energy Research Institute, Nuclear Material Technology Development Team, P.O. Box 105, Dukjin-dong, Yusong-gu, Taejeon, Republic of Korea. Tel.: q82-42868-2759; fax: q82-42-868-8549. E-mail address: [email protected] (M.H. Seo).
stress reducers has been recommended for thick deposition. Nevertheless, most research on Ni electrodeposition from the sulfamate bath was focused on pure Ni rather than Ni alloy w12–15x. The main objective of this work is to develop a Ni– P electrodeposition technology from a sulfamate bath for application to the repair of fault steam generator tubing in nuclear power plants w16,17x. The electrodeposits need to have high process efficiency and superior material properties, especially residual stress of the deposit. In this preliminary study, the effect of H3PO3 concentration on Ni–P electrodeposition from the sulfamate bath and the properties of the deposited layer with heat treatment were investigated. The results of this study show that current efficiency and residual stress of the deposits obtained from a sulfamate bath are higher and lower, respectively, than those from the sulfate bath. These results are unique, because no such data have yet been reported. Moreover, previous research on the microstructure of Ni–P alloys obtained by electroless and electrolytic deposition are mainly focused on the structural change from the amorphous phase to the crystalline one at a relatively high phosphorus content
0257-8972/04/$ - see front matter 䊚 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972Ž03.00661-3
M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
136 Table 1 Bath compositions Sulfamate bath Ni(SO3NH2)2 H3BO3 H3PO3
Sulfate bath 1.39 M 0.65 M 0–0.18 M
NiSO4 H3BO3 H3PO3
1.43 M 0.65 M 0–0.18 M
over several weight percent w18–21x, and the effects of various anions in electrodeposited nickel on the submicrostructure of the deposits w22x. This study on Ni–1.5 wt.% P electrodeposits from a sulfamate bath shows that the microstructure of the deposit consists of dislocation cells with grains surrounded by highly dense dislocations, and the concentration profile of the cross section in the deposit with the thickness is uniform as confirmed by EPMA rather than changed regularly as reported by Despic and Jovic w23x. This is the first report showing the needle shaped precipitation of Ni3P in the microstructure of the deposited layer. 2. Experimental 2.1. Process Ni sulfamate or sulfate as a Ni source, phosphorus acid as a P source, Pt plated Ti with a surface area of 5=6 cm2 as an anode and alloy 600 plate with a surface area of 2=2 cm2 as a cathode were used in Ni–P alloy electrodeposition, respectively. Table 1 shows bath compositions used in this study. Conventional sulfamate bath contains small content of nickel chloride, increasing internal stress in the deposits, but it was not used in this experiment. Ni–P alloy electrodepositions were performed in sulfamate and sulfate baths with the same electrolysis condition as follows: temperature 50 8C, current density 10 Aydm2, pH 1, deposition time 60 min and agitation speed 70 rpm using a stirrer bar. pH was adjusted by sulfamic and sulfuric acids in sulfamate and sulfate baths, respectively. The cathode was polished to 噛1500 emery paper and ultrasonically cleaned in alkaline solution, followed by activation treatment in a 10 wt.% H2SO4 solution for 10 s at 60 8C. The deposit could be separated easily from the substrate due to the weak adhesion between the deposit and the oxide layer already existing in the surface of substrate.
(electron probe micro analyzer, Model SX-50 (CAMECA)). The deposit from sulfamate bath was heat-treated at a temperature in the range of 20–850 8C for 1 h under vacuum of 10y3 torr and was cooled in air. TEM microstructure of the specimen was investigated using Jeol 2000FX equipped with Oxford Link (Model ISIS5947) EDX. Thin foil was prepared by jet polishing using 60% methanolq35% n-butyl alcoholq5% perchloric acid solution at y30 8C, and DC 20 V. A carbon replica was manufactured as follows. Firstly, the sample was electrochemically etched into the 98% methanolq 2% hydrochloric acid solution at DC 6 V for 15 s. Secondly, the etched sample was coated by carbon, and thirdly the carbon coated layer was separated from the substrate. The hardness was measured with a load of 100 gf using the Vickers Hardness Tester (MXT-CX (Matssuzawa)). Thermal analysis was performed by DSC-50 (Matssuzawa) under the condition of Ar 30 mlymin and heating rate 20 8Cymin. 3. Results and discussion 3.1. Phosphorus content Fig. 1 shows variation of phosphorus content in the deposit with H3PO3 concentration in electrolytic solutions. Phosphorus content in both deposits from sulfamate and sulfate baths increased with increasing H3PO3 concentration, consistent with the results reported elsewhere w24,25x. For deposition from sulfamate bath, phosphorus content in the deposit increased from 0.2 to 0.9 wt.% P with increasing H3PO3 concentration from 0.007 to 0.018 M. For deposition from sulfate bath, the phosphorus content in the deposit was higher than that in the deposit from sulfamate bath. From the results of alloy compositions in the deposit, it was found that phosphorus was more readily incorporated during the electrodeposition from the sulfate bath than the sulfamate bath.
2.2. Analysis Alloy composition analysis of the deposit was performed using ICP analyzer (Model JY80C (Jobin Yvon)). Stress in the deposit was measured in-situ using a spiral contractometer (QCI). Line analysis of alloy composition with thickness from the interface of the depositysubstrate to surface of the deposit at cross section of the deposit was performed using EPMA
Fig. 1. Phosphorus content in the deposit with H3PO3 concentration from sulfamate and sulfate baths.
M.H. Seo et al. / Surface and Coatings Technology 176 (2004) 135–140
Fig. 2. Current efficiency with H3PO3 concentration from sulfamate and sulfate baths.
3.2. Current efficiency Cathodic current efficiencies of Ni–P deposition in sulfamate and sulfate baths are shown in Fig. 2. The current efficiency could be calculated from Faraday’s law using the measured weight change and the known composition of the deposit. Current efficiencies decreased with the increasing H3PO3 concentration in the baths, irrespective of the bath. It has been reported that current efficiencies decreased with increasing H3PO3 concentration in chloride and citrate baths, consistent with the results of this work w26,27x. The current efficiency in sulfamate baths was higher than that in sulfate baths and the difference in current efficiency between two baths increased with increasing H3PO3 concentration. Vitkova et al. w28x reported that the decrease of the current efficiency with increasing NaH2PO2 concentration during Ni–Fe–P alloy electrodeposition was caused by a change of hydrogen overvoltage upon the alloys having various compositions. Karayannis et al. w29x reported that the current efficiency in a chloride bath was higher than that in a sulfate bath, while the sulfate ion in the sulfate bath affects the hydrogen evolution more strongly than the chloride ion in the chloride bath. Accordingly, it can be expected that H3PO3 concentration in the baths affected hydrogen over-voltage by change of the Ni–P alloy composition in the deposit during electrodeposition and the sulfate anion rather than sulfamate anion can assist effectively side reaction such as the hydrogen evolution.
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sulfamate bath showed about a half lower stress than that from sulfate bath. Stress in the deposit originates from the co-deposition of hydrogen and metal during electrodeposition w30,31x. Burchardt w32x reported that the rate of the hydrogen evolution reaction was expressed as a function of the phosphorus content in the NiPx alloy (-6.7 wt.% P) and hydrogen adsorption in the deposit was proportional to hydrogen evolution during electrodeposition from a sulfate bath containing NaH2PO2. Under these circumstances, it can be presumed that hydrogen absorption and evolution reactions increased leading to an increase of the stress in the deposit as the H3PO3 concentration in the baths increased, i.e. the phosphorus content in the deposits increased. Consistently, the stress in the deposit from the sulfate bath, where the phosphorus could be more readily incorporated was higher than that from the sulfamate bath. 3.4. Cross-section Fig. 4a is an optical micrograph for cross section of the deposit showing laminar structure. Numerous laminar lines were observed over the whole deposit. Laminar lines in the overdeposited region are shown in Fig. 4b at the edge of the deposit. These laminar lines seem to be formed along the equipotential line during electrodeposition. Dini w33x and Chassaing et al. w34x reported that laminar structure was shown in the alloy such as electrodeposited Au–Cu, Co–P, Co–W and Ni–Mo. Despic and Jovic w23x claimed that laminar structure was formed by repeating the process in which the partial current of one species increases as the partial current of the other species decreases during the electrodeposition of Cu–Pb binary alloy applying the direct current and was thereby composed of multilayers with two kinds of compositions in binary alloy electrodeposition system. Fig. 5 is the result of a line analysis by EPMA. Unlike the model proposed by Despic and Jovic w23x, a variation in the composition of Ni–P alloy with thick-
3.3. Stress Fig. 3 shows stress in the deposit with H3PO3 concentration in the sulfamate and sulfate baths. Stress in the deposit linearly increased from 45.9 to 74.8 MPa and from 106 to 144.8 MPa, respectively, as the H3PO3 concentration in the sulfamate and sulfate baths increased. The measured stress for the deposit from
Fig. 3. Stress in the deposit with H3PO3 concentration from sulfamate and sulfate baths.
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Fig. 4. Optical photographs showing cross-section (a) in the center and (b) at the edge of the Ni–P electrodeposit.
ness from interface of the depositysubstrate to the surface of the deposit was so small that it could be ignored indicating the composition of the alloy with a uniform thickness. Thus, nickel must be involved in electrodeposition of Ni–P alloys, because phosphorus cannot be directly electrodeposited in aqueous solution w35x. 3.5. Microstructure Fig. 6 shows the microstructure of Ni–1.52 wt.% P deposit from sulfamate bath with heat treatment temperature in the range of 20–850 8C for 1 h. Fig. 7 shows the mean size of grain and precipitate shown in Fig. 6. The deposit had dislocation cell structure with grain surrounded by highly dense dislocations as shown in Fig. 6a. Twins were not shown in this study as observed by others w36x. The mean size of grains at 20 8C was 123 nm. After heat treatment at 343 8C, Ni3P precipitates (identified by EDX and electron diffractions) appeared mainly at grain boundary and only a few precipitates smaller in size were observed in the grain interior,
Fig. 5. Depth profiles of Ni and P concentrations obtained from EPMA result of the electrodeposited Ni–P alloy.
Fig. 6. TEM micrographs with heat treatment at temperature of (a) 20; (b) 343; (c), (d) 490; (e), (f) 580; (g) 700; (h) 850 8C, respectively. Fig. 6 (e) micrograph was prepared by carbon replica method.
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increasing heat treatment temperature. Precipitates along grain boundary and in grains resembled polyhedral and circle shapes, respectively, as shown in Fig. 6h. 3.6. Hardness
Fig. 7. The mean size of the grain and precipitate as a function of heat treatment temperature in the range of 20–850 8C.
whereas the mean size of grain was nearly invariant compared to the grain size at 20 8C as shown in Fig. 6b. The retardation of grain growth during heat treatment at 343 8C seems to be due to a Zener drag effect w37x. Rapid grain growth at a temperature of 490 8C occurred and hence the mean size of grain at 490 8C reached 620 nm as shown in Fig. 6c and Fig. 7. Rapid grain growth was concerned with the coarsening of Ni3P precipitates leading to the reduction in the grain boundary pinning force. After heat treatment at 490 8C, needle-like Ni3P precipitates (identified by EDX) were observed as shown in Fig. 6d unlike the round shaped precipitates of Fig. 6c. According to the analysis of carbon replicas as shown Fig. 6e, it was found that the needle type precipitates were accumulated over the deposit nonuniformly and their sizes were much smaller than those of the round type. Therefore, it can be presumed that Ni3P precipitate of needle type precipitated after precipitation of Ni3P precipitates of the round type is already shown above. The deposit was recrystallized after heat treatment at 580 8C for 1 h as shown in Fig. 6f. Dubois et al. w38x reported that temperature of recrystallization of high pure Ni and commercial Ni was 230 and 600 8C, respectively. The precipitates formed at grain boundary could be used as the dislocation accumulation, nucleation and recrystallization sites for the highly cold worked materials, which lowers the activation energies for the transformations w39,40x. Therefore, it seems that the Ni– P electrodeposit could be recrystallized at a lower temperature than that of commercial Ni due to the precipitates existing along grain boundary. Ni3P precipitates within the grain interior increased in size and density during heat treatment at 700 8C as shown in Fig. 6g, compared with the results at 343 8C of Fig. 6b. This seems to be due to the increase of diffusion rate of phosphorus in grain interiors with
Fig. 8 shows the microhardness of Ni–1.52 wt.% P deposit with heat treatment temperature in the range from 20–850 8C for 1 h. Microhardness of the deposit increased from Hv450 to Hv550 until the heat treatment temperature increased to approximately 450 8C. However, microhardness decreased to approximately Hv200 after heat treatment at the higher temperature than 450 8C as the heat treatment temperature increased. Considering the microstructural and microhardness results, it is conceivable to think that the amount of Ni3P precipitate increased and hence the microhardness increased with increasing heat treatment temperature to approximately 450 8C. However, the rapid decrease of microhardness caused by the precipitate coarsening, grain growth and recrystallization appeared as the heat treatment temperature increased to a higher temperature. Muscra et al. w41x reported that hardness of the electro-
Fig. 8. Plot of hardness against heat treatment temperature for 1 h.
Fig. 9. DSC result of Ni-1.52 wt.% P deposit.
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sleeve material with time under isothermal aging at temperature of 600 8C rapidly decreased after 10 min. 3.7. Thermal analysis Fig. 9 shows the result of DSC analysis on a Ni– 1.52 wt.% P deposit. Two exothermic peaks at approximately 310 and 575 8C were observed. The first one at approximately 310 8C seems to be concerned with formation of Ni3P precipitates and the second one at approximately 575 8C is due to recrystallization, respectively, as demonstrated in Fig. 6. 4. Conclusions The effect of H3PO3 concentration on Ni–P electrodeposition from sulfamate and sulfate baths and material properties of the deposit from sulfamate bath with heat treatment in the range of 20–850 8C for 1 h were investigated: 1. As the phosphorus content in the deposit increased, current efficiency slowly decreased, but the stress in the deposit increased. This occurrence appeared more clearly from the sulfate bath where the phosphorus can be readily incorporated than the sulfamate bath. This was explained by the increase of hydrogen evolution and absorption reactions induced by the increase of phosphorus content in the deposit. 2. The size of the grain and precipitate in Ni–1.52 wt.% P deposit from sulfamate bath rapidly increased during heat treatment at temperature above 490 8C, leading to the decrease of microhardness. The microstructural and mechanical properties of the deposit from sulfamate bath with heat treatment were explained by precipitation of Ni3P at 310 8C and recrystallization at 575 8C with the supplemental help of DSC results. References w1x M.G. Fontana, Corrosion Engineering, 3, B and Jo Enterprise, Singapore, 1986, 243. w2x J.E. Williams, C. Davison, J. Electrochem. Soc. 137 (1990) 3260. w3x D. Osmola, P. Nolan, U. Erb, G. Palumbo, K.T. Aust, Phys. Stat. Sol. (a) 131 (1992) 569. w4x A. Robertson, U. Erb, G. Palumbo, Nanostruct. Mater. 12 (1999) 1035. w5x A. Brenner, Electrodeposition of Alloys II, Academic Press, New York, 1963. w6x K. Masui, S. Maruno, T. Yamada, J. Surf. Finish. Soc. Jpn. 41 (11) (1977) 1130. w7x P. Peeters, G. Hoorn, T. Daenen, A. Kurowski, G. Staikov, Electrochim. Acta 47 (2001) 161.
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