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Enhancement in mechanical properties of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid
Materials Science & Engineering A 607 (2014) 505–510
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Materials Science & Engineering A journal homepage: www.elsevier.com/locate/msea
Enhancement in mechanical properties of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid Isao Matsui n,1, Hiroki Mori, Tomo Kawakatsu, Yorinobu Takigawa, Tokuteru Uesugi, Kenji Higashi Department of Materials Science, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 1 March 2014 Received in revised form 8 April 2014 Accepted 10 April 2014 Available online 18 April 2014
A method for enhancement of the mechanical properties of electrodeposited bulk nanocrystalline Fe–Ni alloys was explored. Bulk nanocrystalline Fe–Ni alloys were prepared using electrolytes that primarily consisted of iron sulfate and nickel sulfamate with propionic acid. Varying the concentration of propionic acid in the deposition bath produced no significant change in the C, S, or Ni content or grain sizes of the electrodeposited alloys. In contrast, the hardness of bulk nanocrystalline Fe–Ni alloys increased from 4.0 to 5.0 GPa with the increase of propionic acid concentration from 0 to 3.0 g/L. In addition, the tensile strength also increased from 1.6 to 1.7 GPa while maintaining a good tensile ductility of 10%. These increases for electrodeposited alloys can be explained by grain boundary relaxation strengthening. After annealing at relatively mild temperatures, the alloys electrodeposited without propionic acid exhibited higher strength than at the as-deposited state, while the strength of the alloys electrodeposited using 3.0 g/L propionic acid remained unchanged. The results of this study indicate that the addition of propionic acid to the deposition bath could remove the excess grain boundary defects of Fe–Ni alloys in as-deposited states, requiring no additional thermal treatments and enhancing the mechanical strength to high levels. & 2014 Elsevier B.V. All rights reserved.
Key words: Nanocrystalline metals Electrodeposition Fe–Ni alloys Mechanical properties Grain boundary relaxation
1. Introduction Electrodeposition processes for Fe–Ni alloys have the potential to improve and facilitate understanding of the mechanical behavior of steel and other ferrous alloys with grain sizes less than 100 nm [1]. There are several studies that have investigated the phase transitions [2–5], microstructures [6], and mechanical properties [7–10] of nanocrystalline Fe–Ni alloys. With a Ni content greater than 40 wt%, the electrodeposited alloys show a single-phase face centered cubic (fcc) structure [2]. The electrodeposited bulk nanocrystalline Fe–Ni alloys with an fcc structure exhibit high tensile ductility of 410% [10]. However, they have lower mechanical strength compared with that of the alloys with a body centered cubic (bcc) structure. The tensile strength of nanocrystalline Fe alloys with an fcc structure is 1.6 GPa, even when the grain size decreases to 10–20 nm [10], while those with a bcc structure exhibit a higher strength of 2.1 GPa [11]. Further improvement of n
Corresponding author. Tel.: þ 81 72 254 9313; fax: þ 81 72 254 9912. E-mail address: [email protected] (I. Matsui). 1 Present address: Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology, 2266-98 Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan. http://dx.doi.org/10.1016/j.msea.2014.04.042 0921-5093/& 2014 Elsevier B.V. All rights reserved.
the strength in electrodeposited bulk nanocrystalline Fe–Ni alloys by grain refinement is limited because the alloys show an inverse Hall–Petch behavior as the grain size decreases to 15 nm [10]. In addition to grain size refinement, alloying elements and second phase particles can affect the strength of nanocrystalline materials [12]. Addition of interstitial carbon up to 2% is known to effectively increase the mechanical strength of coarse-grained steels. This phenomenon can be primarily corroborated by the dislocation theory through experimental and/or theoretical evidence that interstitial carbon in the Fe matrix produces a large misfit strain [13–16]. As the grain size reaches the nanometer range, traditional intragranular dislocation mechanisms for plasticity are suppressed, and deformation is dominated by grain boundary processes [17–19]. Some studies [20–22] performed using first-principle calculations indicated that the grain boundary embrittlement is governed by the change in the grain boundary cohesive energy. They also revealed that carbon is a strengthening element for Fe grain boundaries. In either case, addition of carbon as interstitial solute atoms to Fe and its alloys is an effective way to improve the mechanical properties. In the case of electrodeposition processes, Izaki et al. [23–25] demonstrated a simple method of adding carboxylic acids to iron sulfate solutions to produce Fe–C alloys with C content of 4 wt%.
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The electrodeposited Fe–C alloys had a hardness of 8 GPa. Further improvement in the mechanical strength of bulk nanocrystalline Fe–Ni alloys with an fcc structure may be achieved by electrodeposition using a carboxylic acid. However, the current application of increasing strength through the use of carboxylic acids has been confined to Fe-based metals with a bcc structure [23–25]. Therefore, in this study, we prepared a set of bulk nanocrystalline Fe–Ni alloys by electrodeposition using various concentrations of propionic acid. Mechanical measurements of these alloys demonstrated an unexpected strengthening behavior that is considerably more pronounced than predicted on the basis of solid solution strengthening from carbon. The strengthening resulting from the addition of propionic acid is discussed on the basis of grain boundary relaxation.
2. Experimental procedure Fe–Ni alloys were prepared using an electrodeposition system with varying concentrations of propionic acid in the deposition bath. The details of the bath compositions used in this study are described in Table 1. Prior to deposition for bulk samples, thick foils with dimensions 40 mm 30 mm 0.3 mm were deposited by electrodeposition for 48 h in a 1 L bath; these are referred to as “thick” samples. The bulk alloys with dimensions 50 mm 40 mm 0.8 mm for tensile tests were deposited by electrodeposition for 168 h in a 5 L bath; these are referred to as “bulk” samples. The only difference between the 1 L and 5 L baths was their capacity; the construction of the electrodeposition system is given in Ref. [26]. We have confirmed that the alloys electrodeposited using both 1 L and 5 L baths with the same conditions had nearly identical characteristics. All samples were deposited on Cu substrates of commercial purity using two counter electrodes of titanium baskets with Fe plates (99.8%) and Ni plates (99.98%). All the electrodeposition processes were run at a current density of 10 mA/cm2, bath temperature of 50.0 70.5 1C, and pH of 2.2 7 0.1. The bath temperature was strictly maintained by a heater using a proportional–integral–derivative controller. The pH of the solutions was maintained by adding drops of either 1.0 mol/L sulfamic acid or 5.0 mol/L sodium hydroxide. The Ni content of the electrodeposits was determined by energy-dispersive X-ray spectrometry (EDS) analysis using a scanning electron microscope (HITACHI S-4800). The carbon and sulfur contents of the electrodeposits were quantified by an IR absorption method after combustion in a high-frequency induction furnace. Transmission electron microscopy (TEM) specimens were prepared. Thin foil specimens with a diameter of 3 mm were fabricated by a twin-jet polishing technique using a nitric acid– methanol solution (20% by volume of HNO3) at 30 1C and 15 V. The TEM specimens were examined using a JEOL JEM-2100F system operated at 200 kV. X-ray diffraction (XRD, RIGAKU Ultimate IV) analysis was performed using Cu Kα radiation to confirm structures and estimate grain sizes. To evaluate the hardness of the electrodeposits, micro-Vickers hardness tests were conducted on Table 1 Bath composition for bulk nanocrystalline Fe–Ni alloys. Chemicals
Amount (g/L)
Purpose
Iron sulfate Nickel sulfamate Propionic acid Nickel chloride Boric acid Saccharin sodium Sodium lauryl sulfate
105.0 175.0 0–3.0 20.0 40.0 5.0 0.3
Fe source Ni source C source Passivation inhibitor Complexing agent Stress reliever Surface acting agent
thick samples using a load of 500 g for 10 s. Each reported data point represents the average of at least 12 indentations. Using the bulk samples, dog-bone specimens with a gauge length of 12 mm, width of 4.0 mm, and thickness of 0.7 mm were machined by electrical discharge machining for tensile tests. It is noted that the copper substrate was removed by mechanical polishing. Tensile tests were performed at a strain rate of 1 10 3 s 1 at room temperature, and the strain was measured using a strain gauge with a maximum measured value of 5.0%. The plastic deformation of the tensile specimen after fracture was measured by the change in the gauge length.
3. Results and discussion In total, six thick samples were electrodeposited by varying the concentration of propionic acid (0, 0.1, 0.5, 1.0, 2.0, and 3.0 g/L). Fig. 1a shows the current efficiency of the deposition bath with propionic acid concentration of 0–3.0 g/L. All deposition baths exhibited a current efficiency of 61%. Propionic acid did not have an effect on the current efficiency. Fig. 1b, c and d shows, respectively, the Ni, C, and S contents of thick samples electrodeposited with varying concentrations of propionic acid in the deposition bath. The Ni and S contents of the thick samples were constant at 42 at% and 0.11 at%, respectively, and they were independent of the propionic acid concentration (Fig. 1b and d). The C content of the thick samples approximately increased from 0.01 to 0.09 at% with propionic acid concentration (Fig. 1c). The average values presented in Fig. 1 have error values corresponding to the standard deviation. Fig. 2 shows the bright-field TEM images from selected samples across the range of propionic acid concentrations. The alloys electrodeposited without propionic acid (Fig. 2a) exhibit microstructures with a grain size of 15 nm. Furthermore, the same microstructure is observed in the TEM images from Fe–Ni alloys electrodeposited using 1.0 and 3.0 g/L, as shown in Fig. 2b and c, respectively. No defined precipitate was observed in the TEM microstructure. The XRD pattern from the thick samples shows a single fcc structure (Fig. 3). The grain sizes of these nanocrystalline Fe–Ni alloys were estimated from the (111) diffraction peak width using Scherrer's equation, and the results are presented in Fig. 3. The calculated grain sizes ranged from 13 to 14 nm, which are comparable with the sizes observed in TEM images. The results from the TEM observations and estimation from the XRD peak width indicate that the grain size of electrodeposited alloys was independent of the C content. In summary, the varying concentration of propionic acid in the deposition bath changed the C content of electrodeposited alloys. The concentration adjustments did not have an effect on the current efficiency of the deposition bath, Ni and S contents, or grain sizes. Apparently, we could produce idealized samples for investigating the effect of C content on the mechanical properties of electrodeposits. On the other hand, the C content of the Fe–Ni alloys for this study ( 0.02 wt%) was much lower than that of the Fe–C alloys electrodeposited using propionic acid ( 0.60 wt%) [23]. This difference is related to the structures of the electrodeposits. To confirm the effect of structure, we conducted electrodeposition with decreasing Ni/Fe molar ratio in the deposition bath from 1.66 to 1.54. The C content of the Fe–Ni alloys electrodeposited using 1.5 g/L propionic acid increased to 0.54 wt% with a decrease in the Ni content, and the structure changed from fcc to bcc. This result indicates that the addition of a carboxylic acid to the deposition bath has poor efficacy for increasing C content, particularly in the case of electrodeposition of Fe–Ni alloys with an fcc structure. The mechanical behavior of the thick samples was investigated by performing a micro-Vickers hardness test. Fig. 4a shows the test
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Fig. 1. (a) Current efficiency of the deposition bath and (b) Ni content, (c) C content, and (d) S content of electrodeposited alloys as a function of the concentration of propionic acid in the deposition bath.
Fig. 2. Bright-field TEM images of bulk Fe–Ni alloys electrodeposited using propionic acid concentrations of (a) 0, (b) 1.0, and (c) 3.0 g/L.
Fig. 3. XRD patterns of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid of 0–3.0 g/L. P stands for the concentration of propionic acid in the deposition bath and d stands for the grain size calculated from XRD determination of the (111) peak width.
results plotted against the concentration of propionic acid. A homogeneous hardness was observed in all samples. The standard deviation in the hardness values was less than 0.04 GPa. The
hardness values increased from 4.0 to 5.0 GPa as the concentration of propionic acid increased from 0 to 3.0 g/L. However, the grain sizes of all the samples were almost equal at d 13 nm. The change in hardness for bulk nanocrystalline Fe–Ni alloys is plotted against C content in Fig. 4b. This shows that the increase in the hardness is independent of the C content. Moreover, the strengthening due to propionic acid addition is considerably more pronounced than the predicted solid solution strengthening arising from octahedralinterstitial carbon for Ni–C binary alloys [27], as shown by the comparison in Fig. 4b. For further investigation of the effect of propionic acid addition to the deposition bath on mechanical properties, two bulk samples were prepared by electrodeposition with propionic acid concentrations of 0 and 3.0 g/L. The representative stress–strain curves of both bulk samples are shown in Fig. 5. The tensile strength and plastic elongation after fracture determined from these tests are summarized in Table 2. The tensile strengths of bulk samples prepared using propionic acid at 0 and 3.0 g/L were 1.63 and 1.73 GPa, respectively. Tensile strength increase for bulk nanocrystalline Fe–Ni alloys with propionic acid addition was observed as well as seen from the hardness tests (Fig. 4a). In addition to good tensile strength, the bulk samples exhibited high tensile ductility of 10%. The inset image in Fig. 5 shows actual specimens of the alloys electrodeposited using 3.0 g/L
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Fig. 4. (a) Hardness of bulk nanocrystalline Fe–Ni alloys as a function of the concentration of propionic acid in the deposition bath. (b) Change in hardness for bulk nanocrystalline Fe–Ni alloys as a function of the C content. The solid line shows a prediction based on solid solute strengthening arising from octahedral-interstitial carbon for Ni–C binary alloys [27].
Fig. 5. Representative stress–strain curves of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid concentrations of 0 and 3.0 g/L. The strain was measured using a strain gauge with a maximum measured value of 5.0%. The elongation after fracture was obtained experimentally by comparing the gauge length before and after the tensile test. The inset image shows the actual specimen of the alloys electrodeposited using 3.0 g/L propionic acid after fracture.
Table 2 Mechanical properties of electrodeposited bulk nanocrystalline Fe–Ni alloys in the as-deposited state and after grain boundary relaxation by propionic acid addition and thermal treatments. Propionic acid (g/L)
Annealing at 200 1C
Hardness (GPa)
Strength (GPa)
Elongation (%)
0 3.0 0
– – Applied
4.0 7 0.02 5.0 7 0.04 5.0 7 0.01
1.63 7 0.02 1.737 0.03 1.75 7 0.03
12.7 7 1.4 10.7 7 0.6 4.2 7 0.4
propionic acid after the tensile fracture; here plastic deformation can be seen. A number of studies have reported that in their as-deposited or as-prepared state, nanocrystalline metals often contain nonequilibrium grain boundaries with excess dislocation, misfit regions, or excess free volume [28–30]. A low-temperature annealing process is also shown to release excess defects without any measurable change in grain size or texture; this is termed as grain boundary relaxation. In fact, Jang and Atzmon [29] suggested,
based on high resolution TEM observations, that grain boundaries evolve gradually during low temperature annealing from an initial discontinuous structure into more equilibrium structures. In addition, several studies reported that low-temperature treatments can increase hardness and tensile strength [31,32]. Grain boundary relaxation is expected to reduce the dislocation sources and result in higher hardness for the same or similar grain size [33]. As grain sizes reach nanometer range, the grain boundary state has a key role in the mechanical properties in addition to the grain sizes [34]. The results of mechanical measurements in this study show a 25% increase in the hardness of electrodeposited bulk nanocrystalline Fe–Ni alloys upon addition of propionic acid to the deposition bath, and the addition rarely produces a change in the grain sizes or Ni, S, and C contents of the electrodeposits. There is a probability that the addition of propionic acid results in grain boundary relaxation, even in the as-deposited state, without requiring additional thermal treatments. To explore the potency, additional three thick samples were electrodeposited using propionic acid concentrations of 0, 1.0, and 3.0 g/L, and all samples were annealed at 200 1C for a total of 2 h. Grain boundary relaxation occurs at approximately 400 1C or lower for Fe-based alloys [33,35]. XRD analysis and micro-Vickers hardness tests were also conducted at each interval. Fig. 6 shows the XRD patterns of the samples in the as-deposited state and after the 200 1C treatment. This shows that the thermal treatments applied in this study did not cause any obvious changes to the microstructure of the samples. The grain sizes remained unchanged after annealing. Hardness values are plotted against annealing time in Fig. 7. Thermal treatments resulted in an increase in the hardness, and the hardening behavior varied with the propionic acid concentration. The hardness of the nanocrystalline Fe–Ni alloys electrodeposited without propionic acid drastically increased from 4.3 GPa to 5.1 GPa, an increase of 20%. The alloys electrodeposited using 1.0 and 3.0 g/L propionic acid after annealing had a higher hardness in the as-deposited state with 10% and 4% increases in the hardness, respectively. Moreover, Rupert et al. [34] reported a 20% increase in the hardness for Ni–W alloys due to grain boundary relaxation. There is a slight strengthening of the grain boundary relaxation for the sample electrodeposited using propionic acid compared to the reported behavior and the sample electrodeposited without propionic acid. Moreover, the magnitude of the hardness plateau for the annealed alloys is comparable to that of the alloys electrodeposited using 3.0 g/L propionic acid in the asdeposited state. This agreement indicates that addition of propionic acid to the deposition bath can result in equilibrium structures in electrodeposited Fe–Ni alloys even in the as-deposited state,
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Fig. 6. XRD patterns for bulk nanocrystalline Fe–Ni alloys electrodeposited using (a) 0 and (b) 3.0 g/L propionic acid upon annealing at 200 1C for 2 h. P stands for the concentration of propionic acid in the deposition bath and d stands for the grain size calculated from XRD determination of the (111) peak width.
Fig. 7. Hardness versus annealing time for bulk nanocrystalline Fe–Ni alloys electrodeposited using 0, 1.0, and 3.0 g/L propionic acid for annealing temperatures at 200 1C. P stands for concentration of propionic acid in the deposition bath.
and the reduction excess grain boundary defects cause higher hardness. We applied annealing to bulk nanocrystalline Fe–Ni alloys electrodeposited without propionic acid and evaluated the tensile properties to compare the effect of grain boundary relaxation by thermal treatments and propionic acid addition on the tensile behavior. The thermal treatments resulted in an increase in the hardness to 5.0 GPa; this corresponded to the addition of 3.0 g/L propionic acid (Table 2). The representative stress–strain curves of the alloys electrodeposited without propionic acid upon the thermal treatments at 200 1C are shown in Fig. 8, and the results are given in Table 2 and Fig. 9. Fig. 9 shows that the thermal treatments increased the tensile strength to 1.76 GPa, and this value is comparable to that of the alloys electrodeposited using 3.0 g/L propionic acid. This indicates that the increases of the tensile strength for bulk nanocrystalline Fe–Ni alloys with propionic acid addition were also resulted from the reduction of excess grain boundary defects. On the other hand, the tensile strength of the electrodeposited alloys rises only by 6% with the addition of propionic acid, while the hardness rises by 25%. The difference of the strengthening effect would be caused by a different deformation mechanism for tensile and compression. The annealed bulk nanocrystalline Fe–Ni alloys exhibited lower tensile ductility than the alloys electrodeposited using propionic acid (Fig. 9). The Fe–Ni alloys after annealing showed a tensile ductility of 4%, while the alloys electrodeposited using 3.0 g/L propionic acid showed ductility of 11%. Impurity segregation is often detrimental to ductility. Grain boundary fracture on
Fig. 8. Representative tensile behaviors of bulk nanocrystalline Fe–Ni alloys electrodeposited using no propionic acid in the as-deposited state and after annealing at 200 1C. The strain was measured using a strain gauge with a maximum measured value of 5.0%. The thermal treatment was applied to increase the hardness to values that correspond with those of the alloys electrodeposited using propionic acid of 3.0 g/L in the as-deposited state.
Fig. 9. Comparison of the effect of grain boundary relaxation by thermal treatments and propionic acid addition on the tensile properties.
coarse-grained Fe–Ni alloys is caused by segregation of sulfur, which weakens the grain boundary cohesion [22,36]. Moreover, Fe–Ni alloys show more sulfur-induced embrittlement than
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Fe-based alloys and steels [37]. A very low sulfur concentration of 10 ppm is enough to cause ductility loss in the Fe–Ni alloys [38,39]. In addition, Klement et al. [40] and Wang et al. [32] investigated using EDS and electron energy-loss spectroscopy techniques the segregation of impurities in grain boundaries by annealing in electrodeposited nanocrystalline Ni. Both studies detected sulfur segregation in the grain boundaries on nanocrystalline Ni annealed at 200–250 1C. On the other hand, both studies did not detect any obvious segregation of carbon, which is the grain boundary cohesion enhancer, in the grain boundaries [22,36]. It is possible that the sulfur segregation happens by annealing for grain boundary relaxation in electrodeposited bulk nanocrystalline Fe–Ni alloys and results in the reduction of tensile ductility. In contrast, propionic acid addition for grain boundary relaxation is at low risk for segregation of sulfur in the grain boundaries, and it could increase the tensile strength while maintaining a high tensile ductility of 10%. 4. Conclusions 1. In electrodeposition for Fe–Ni alloys with an fcc structure, addition of propionic acid to the deposition bath slightly affected the C content of the electrodeposits compared with Fe–Ni alloys with a bcc structure. Moreover, the addition of propionic acid had no effect on the current efficiency of the deposition bath, grain sizes, or Ni or S contents of the electrodeposited alloys. 2. Addition of propionic acid to the deposition bath can significantly increase the hardness of electrodeposited nanocrystalline Fe–Ni alloys. An increase in the hardness of 25%, amounting to 1.0 GPa, was observed as the concentration of propionic acid increased to 3.0 g/L. The strengthening is much larger than expected for solid solution strengthening arising from octahedral-interstitial carbon for Ni–C binary alloys. 3. The results of tensile tests showed an enhanced tensile strength of 1.7 GPa in bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid compared to those electrodeposited without propionic acid. In addition to the high tensile strength, the bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid exhibited a high tensile ductility of 10%. 4. Low temperature annealing at 200 1C can increase the hardness of Fe–Ni alloys deposited without propionic acid from 4.3 to 5.1 GPa, but the treatments rarely influence the hardness of the alloys deposited with propionic acid. The hardness values after annealing are comparable to that of alloys deposited with 3.0 g/L propionic acid in the as-deposited state. 5. The results of thermal treatments in this study and discussion based on the grain boundary relaxation strengthening indicate that the addition of propionic acid produced more equilibrium structures on the electrodeposited alloys. The relaxation of excess grain boundary defects by propionic acid addition could result in higher hardness and tensile strength, along with a high ductility of 10%, in electrodeposited bulk nanocrystalline Ni–Fe alloys.
Acknowledgments This study was supported by a Grant-in-Aid for Scientific Research from (C) (25390031) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan and a Grant-in-Aid for JSPS Fellows.
References [1] C. Cheung, F. Djuanda, U. Erb, G. Palumbo, Nanostructured Mater. 5 (1995) 513–523. [2] D.L. Grimmett, M. Schwartz, K. Nobe, J. Electrochem. Soc. 140 (1993) 973–979. [3] S.D. Leith, S. Ramli, D.T. Schwartz, J. Electrochem. Soc. 146 (1999) 1431–1435. [4] A. Sanaty-Zadeh, K. Raeissi, A. Saidi, J. Alloys Compd. 485 (2009) 402–407. [5] C. Rousse, P. Fricoteaux, J. Mater. Sci. 46 (2011) 6046–6053. [6] F. Czerwinski, Electrochim. Acta 44 (1998) 667–675. [7] H. Li, F. Ebrahimi, Mater. Sci. Eng. A 347 (2003) 93–101. [8] Y.M. Yeh, G.C. Tu, T.H. Fang, J. Alloys Compd. 372 (2004) 224–230. [9] H. Li, F. Ebrahimi, Acta Mater. 54 (2006) 2877–2886. [10] I. Matsui, T. Kawakatsu, Y. Takigawa, T. Uesugi, K. Higashi, Mater. Lett. 116 (2014) 71–74. [11] B. Srinivasarao, K. Oh-ishi, T. Ohkubo, K. Hono, Acta Mater. 57 (2009) 3277–3286. [12] R.K. Guduru, R.O. Scattergood, C.C. Koch, K.L. Murty, S. Guruswamy, M. K. McCarter, Scr. Mater. 54 (2006) 1879–1883. [13] V.G. Gavriljuk, V.N. Shivanyuk, B.D. Shanina, Acta Mater. 53 (2005) 5017–5024. [14] L. Cheng, A. Bö ttger, T.H. de Keijser, E.J. Mittemeijer, Scr. Metall. Mater. 24 (1990) 509–514. [15] C.P. Scott, J. Drillet, Scr. Mater. 56 (2007) 489–492. [16] D.J. Hepburn, D. Ferguson, S. Gardner, G.J. Ackland, Phys. Rev. B 88 (2013) 024115. [17] Z. Budrovic, H. Van Swygenhoven, P.M. Derlet, S. Van Petegem, B. Schmitt, Science 304 (2004) 273–276. [18] H. Van Swygenhoven, P.M. Derlet, Phys. Rev. B 64 (2001) 2241051–2241059. [19] J.W. Cahn, Y. Mishin, A. Suzuki, Acta Mater. 54 (2006) 4953–4975. [20] R. Wu, A.J. Freeman, G.B. Olson, Phys. Rev. B 53 (1996) 7504–7509. [21] R. Wu, A.J. Freeman, G.B. Olson, Science 265 (1994) 376–380. [22] M. Yamaguchi, Metall. Mater. Trans. A 42 (2011) 319–329. [23] Y. Fujiwara, T. Nagayama, A. Nakae, M. Izaki, H. Enomoto, E. Yamauchi, J. Electrochem. Soc. 143 (1996) 2584–2590. [24] M. Izaki, T. Omi, Metall. Mater. Trans. A 27 (1996) 483–486. [25] Y. Fujiwara, M. Izaki, H. Enomoto, T. Nagayama, E. Yamauchi, A. Nakae, J. Appl. Electrochem. 28 (1998) 855–862. [26] I. Matsui, Y. Takigawa, T. Uesugi, K. Higashi, Mater. Sci. Eng. A 578 (2013) 318–322. [27] I. Matsui, T. Uesugi, Y. Takigawa, K. Higashi, Acta Mater. 61 (2013) 3360–3369. [28] X.L. Wu, Y.T. Zhu, Appl. Phys. Lett. 89 (2006) 031922. [29] D. Jang, M. Atzmon, J. Appl. Phys. 99 (2006) 083504. [30] S. Ranganathan, R. Divakar, V.S. Raghunathan, Scr. Mater. 44 (2001) 1169–1174. [31] A.J. Detor, C.A. Schuh, J. Mater. Res. 22 (2007) 3233–3248. [32] Y.M. Wang, S. Cheng, Q.M. Wei, E. Ma, T.G. Nieh, A. Hamza, Scr. Mater. 51 (2004) 1023–1028. [33] H. Kotan, K.A. Darling, M. Saber, R.O. Scattergood, C.C. Koch, J. Mater. Sci. 48 (2013) 1–10. [34] T.J. Rupert, J.R. Trelewicz, C.A. Schuh, J. Mater. Res. 27 (2012) 1285–1294. [35] H. Kotan, M. Saber, C.C. Koch, R.O. Scattergood, Mater. Sci. Eng. A 552 (2012) 310–315. [36] M. Yamaguchi, M. Shiga, H. Kaburaki, J. Phys.: Condens. Matter 16 (2004) 3933–3956. [37] T. Tanaka, H. Sawada, ISIJ Int. 53 (2013) 1289–1291. [38] L. Ben Mostefa, G. Saindrenan, M.P. Solignac, J.P. Colin, Acta Metall. Mater. 39 (1991) 3111–3118. [39] M.T. Perrot-Simonetta, A. Kobylanski, J. Phys. IV 05 (1995) C7-323–C7-334. [40] U. Klement, U. Erb, A.M. El-Sherik, K.T. Aust, Mater. Sci. Eng. A 203 (1995) 177–186.
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Enhancement in mechanical properties of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid Isao Matsui n,1, Hiroki Mori, Tomo Kawakatsu, Yorinobu Takigawa, Tokuteru Uesugi, Kenji Higashi Department of Materials Science, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 1 March 2014 Received in revised form 8 April 2014 Accepted 10 April 2014 Available online 18 April 2014
A method for enhancement of the mechanical properties of electrodeposited bulk nanocrystalline Fe–Ni alloys was explored. Bulk nanocrystalline Fe–Ni alloys were prepared using electrolytes that primarily consisted of iron sulfate and nickel sulfamate with propionic acid. Varying the concentration of propionic acid in the deposition bath produced no significant change in the C, S, or Ni content or grain sizes of the electrodeposited alloys. In contrast, the hardness of bulk nanocrystalline Fe–Ni alloys increased from 4.0 to 5.0 GPa with the increase of propionic acid concentration from 0 to 3.0 g/L. In addition, the tensile strength also increased from 1.6 to 1.7 GPa while maintaining a good tensile ductility of 10%. These increases for electrodeposited alloys can be explained by grain boundary relaxation strengthening. After annealing at relatively mild temperatures, the alloys electrodeposited without propionic acid exhibited higher strength than at the as-deposited state, while the strength of the alloys electrodeposited using 3.0 g/L propionic acid remained unchanged. The results of this study indicate that the addition of propionic acid to the deposition bath could remove the excess grain boundary defects of Fe–Ni alloys in as-deposited states, requiring no additional thermal treatments and enhancing the mechanical strength to high levels. & 2014 Elsevier B.V. All rights reserved.
Key words: Nanocrystalline metals Electrodeposition Fe–Ni alloys Mechanical properties Grain boundary relaxation
1. Introduction Electrodeposition processes for Fe–Ni alloys have the potential to improve and facilitate understanding of the mechanical behavior of steel and other ferrous alloys with grain sizes less than 100 nm [1]. There are several studies that have investigated the phase transitions [2–5], microstructures [6], and mechanical properties [7–10] of nanocrystalline Fe–Ni alloys. With a Ni content greater than 40 wt%, the electrodeposited alloys show a single-phase face centered cubic (fcc) structure [2]. The electrodeposited bulk nanocrystalline Fe–Ni alloys with an fcc structure exhibit high tensile ductility of 410% [10]. However, they have lower mechanical strength compared with that of the alloys with a body centered cubic (bcc) structure. The tensile strength of nanocrystalline Fe alloys with an fcc structure is 1.6 GPa, even when the grain size decreases to 10–20 nm [10], while those with a bcc structure exhibit a higher strength of 2.1 GPa [11]. Further improvement of n
Corresponding author. Tel.: þ 81 72 254 9313; fax: þ 81 72 254 9912. E-mail address: [email protected] (I. Matsui). 1 Present address: Materials Research Institute for Sustainable Development, National Institute of Advanced Industrial Science and Technology, 2266-98 Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan. http://dx.doi.org/10.1016/j.msea.2014.04.042 0921-5093/& 2014 Elsevier B.V. All rights reserved.
the strength in electrodeposited bulk nanocrystalline Fe–Ni alloys by grain refinement is limited because the alloys show an inverse Hall–Petch behavior as the grain size decreases to 15 nm [10]. In addition to grain size refinement, alloying elements and second phase particles can affect the strength of nanocrystalline materials [12]. Addition of interstitial carbon up to 2% is known to effectively increase the mechanical strength of coarse-grained steels. This phenomenon can be primarily corroborated by the dislocation theory through experimental and/or theoretical evidence that interstitial carbon in the Fe matrix produces a large misfit strain [13–16]. As the grain size reaches the nanometer range, traditional intragranular dislocation mechanisms for plasticity are suppressed, and deformation is dominated by grain boundary processes [17–19]. Some studies [20–22] performed using first-principle calculations indicated that the grain boundary embrittlement is governed by the change in the grain boundary cohesive energy. They also revealed that carbon is a strengthening element for Fe grain boundaries. In either case, addition of carbon as interstitial solute atoms to Fe and its alloys is an effective way to improve the mechanical properties. In the case of electrodeposition processes, Izaki et al. [23–25] demonstrated a simple method of adding carboxylic acids to iron sulfate solutions to produce Fe–C alloys with C content of 4 wt%.
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The electrodeposited Fe–C alloys had a hardness of 8 GPa. Further improvement in the mechanical strength of bulk nanocrystalline Fe–Ni alloys with an fcc structure may be achieved by electrodeposition using a carboxylic acid. However, the current application of increasing strength through the use of carboxylic acids has been confined to Fe-based metals with a bcc structure [23–25]. Therefore, in this study, we prepared a set of bulk nanocrystalline Fe–Ni alloys by electrodeposition using various concentrations of propionic acid. Mechanical measurements of these alloys demonstrated an unexpected strengthening behavior that is considerably more pronounced than predicted on the basis of solid solution strengthening from carbon. The strengthening resulting from the addition of propionic acid is discussed on the basis of grain boundary relaxation.
2. Experimental procedure Fe–Ni alloys were prepared using an electrodeposition system with varying concentrations of propionic acid in the deposition bath. The details of the bath compositions used in this study are described in Table 1. Prior to deposition for bulk samples, thick foils with dimensions 40 mm 30 mm 0.3 mm were deposited by electrodeposition for 48 h in a 1 L bath; these are referred to as “thick” samples. The bulk alloys with dimensions 50 mm 40 mm 0.8 mm for tensile tests were deposited by electrodeposition for 168 h in a 5 L bath; these are referred to as “bulk” samples. The only difference between the 1 L and 5 L baths was their capacity; the construction of the electrodeposition system is given in Ref. [26]. We have confirmed that the alloys electrodeposited using both 1 L and 5 L baths with the same conditions had nearly identical characteristics. All samples were deposited on Cu substrates of commercial purity using two counter electrodes of titanium baskets with Fe plates (99.8%) and Ni plates (99.98%). All the electrodeposition processes were run at a current density of 10 mA/cm2, bath temperature of 50.0 70.5 1C, and pH of 2.2 7 0.1. The bath temperature was strictly maintained by a heater using a proportional–integral–derivative controller. The pH of the solutions was maintained by adding drops of either 1.0 mol/L sulfamic acid or 5.0 mol/L sodium hydroxide. The Ni content of the electrodeposits was determined by energy-dispersive X-ray spectrometry (EDS) analysis using a scanning electron microscope (HITACHI S-4800). The carbon and sulfur contents of the electrodeposits were quantified by an IR absorption method after combustion in a high-frequency induction furnace. Transmission electron microscopy (TEM) specimens were prepared. Thin foil specimens with a diameter of 3 mm were fabricated by a twin-jet polishing technique using a nitric acid– methanol solution (20% by volume of HNO3) at 30 1C and 15 V. The TEM specimens were examined using a JEOL JEM-2100F system operated at 200 kV. X-ray diffraction (XRD, RIGAKU Ultimate IV) analysis was performed using Cu Kα radiation to confirm structures and estimate grain sizes. To evaluate the hardness of the electrodeposits, micro-Vickers hardness tests were conducted on Table 1 Bath composition for bulk nanocrystalline Fe–Ni alloys. Chemicals
Amount (g/L)
Purpose
Iron sulfate Nickel sulfamate Propionic acid Nickel chloride Boric acid Saccharin sodium Sodium lauryl sulfate
105.0 175.0 0–3.0 20.0 40.0 5.0 0.3
Fe source Ni source C source Passivation inhibitor Complexing agent Stress reliever Surface acting agent
thick samples using a load of 500 g for 10 s. Each reported data point represents the average of at least 12 indentations. Using the bulk samples, dog-bone specimens with a gauge length of 12 mm, width of 4.0 mm, and thickness of 0.7 mm were machined by electrical discharge machining for tensile tests. It is noted that the copper substrate was removed by mechanical polishing. Tensile tests were performed at a strain rate of 1 10 3 s 1 at room temperature, and the strain was measured using a strain gauge with a maximum measured value of 5.0%. The plastic deformation of the tensile specimen after fracture was measured by the change in the gauge length.
3. Results and discussion In total, six thick samples were electrodeposited by varying the concentration of propionic acid (0, 0.1, 0.5, 1.0, 2.0, and 3.0 g/L). Fig. 1a shows the current efficiency of the deposition bath with propionic acid concentration of 0–3.0 g/L. All deposition baths exhibited a current efficiency of 61%. Propionic acid did not have an effect on the current efficiency. Fig. 1b, c and d shows, respectively, the Ni, C, and S contents of thick samples electrodeposited with varying concentrations of propionic acid in the deposition bath. The Ni and S contents of the thick samples were constant at 42 at% and 0.11 at%, respectively, and they were independent of the propionic acid concentration (Fig. 1b and d). The C content of the thick samples approximately increased from 0.01 to 0.09 at% with propionic acid concentration (Fig. 1c). The average values presented in Fig. 1 have error values corresponding to the standard deviation. Fig. 2 shows the bright-field TEM images from selected samples across the range of propionic acid concentrations. The alloys electrodeposited without propionic acid (Fig. 2a) exhibit microstructures with a grain size of 15 nm. Furthermore, the same microstructure is observed in the TEM images from Fe–Ni alloys electrodeposited using 1.0 and 3.0 g/L, as shown in Fig. 2b and c, respectively. No defined precipitate was observed in the TEM microstructure. The XRD pattern from the thick samples shows a single fcc structure (Fig. 3). The grain sizes of these nanocrystalline Fe–Ni alloys were estimated from the (111) diffraction peak width using Scherrer's equation, and the results are presented in Fig. 3. The calculated grain sizes ranged from 13 to 14 nm, which are comparable with the sizes observed in TEM images. The results from the TEM observations and estimation from the XRD peak width indicate that the grain size of electrodeposited alloys was independent of the C content. In summary, the varying concentration of propionic acid in the deposition bath changed the C content of electrodeposited alloys. The concentration adjustments did not have an effect on the current efficiency of the deposition bath, Ni and S contents, or grain sizes. Apparently, we could produce idealized samples for investigating the effect of C content on the mechanical properties of electrodeposits. On the other hand, the C content of the Fe–Ni alloys for this study ( 0.02 wt%) was much lower than that of the Fe–C alloys electrodeposited using propionic acid ( 0.60 wt%) [23]. This difference is related to the structures of the electrodeposits. To confirm the effect of structure, we conducted electrodeposition with decreasing Ni/Fe molar ratio in the deposition bath from 1.66 to 1.54. The C content of the Fe–Ni alloys electrodeposited using 1.5 g/L propionic acid increased to 0.54 wt% with a decrease in the Ni content, and the structure changed from fcc to bcc. This result indicates that the addition of a carboxylic acid to the deposition bath has poor efficacy for increasing C content, particularly in the case of electrodeposition of Fe–Ni alloys with an fcc structure. The mechanical behavior of the thick samples was investigated by performing a micro-Vickers hardness test. Fig. 4a shows the test
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Fig. 1. (a) Current efficiency of the deposition bath and (b) Ni content, (c) C content, and (d) S content of electrodeposited alloys as a function of the concentration of propionic acid in the deposition bath.
Fig. 2. Bright-field TEM images of bulk Fe–Ni alloys electrodeposited using propionic acid concentrations of (a) 0, (b) 1.0, and (c) 3.0 g/L.
Fig. 3. XRD patterns of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid of 0–3.0 g/L. P stands for the concentration of propionic acid in the deposition bath and d stands for the grain size calculated from XRD determination of the (111) peak width.
results plotted against the concentration of propionic acid. A homogeneous hardness was observed in all samples. The standard deviation in the hardness values was less than 0.04 GPa. The
hardness values increased from 4.0 to 5.0 GPa as the concentration of propionic acid increased from 0 to 3.0 g/L. However, the grain sizes of all the samples were almost equal at d 13 nm. The change in hardness for bulk nanocrystalline Fe–Ni alloys is plotted against C content in Fig. 4b. This shows that the increase in the hardness is independent of the C content. Moreover, the strengthening due to propionic acid addition is considerably more pronounced than the predicted solid solution strengthening arising from octahedralinterstitial carbon for Ni–C binary alloys [27], as shown by the comparison in Fig. 4b. For further investigation of the effect of propionic acid addition to the deposition bath on mechanical properties, two bulk samples were prepared by electrodeposition with propionic acid concentrations of 0 and 3.0 g/L. The representative stress–strain curves of both bulk samples are shown in Fig. 5. The tensile strength and plastic elongation after fracture determined from these tests are summarized in Table 2. The tensile strengths of bulk samples prepared using propionic acid at 0 and 3.0 g/L were 1.63 and 1.73 GPa, respectively. Tensile strength increase for bulk nanocrystalline Fe–Ni alloys with propionic acid addition was observed as well as seen from the hardness tests (Fig. 4a). In addition to good tensile strength, the bulk samples exhibited high tensile ductility of 10%. The inset image in Fig. 5 shows actual specimens of the alloys electrodeposited using 3.0 g/L
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Fig. 4. (a) Hardness of bulk nanocrystalline Fe–Ni alloys as a function of the concentration of propionic acid in the deposition bath. (b) Change in hardness for bulk nanocrystalline Fe–Ni alloys as a function of the C content. The solid line shows a prediction based on solid solute strengthening arising from octahedral-interstitial carbon for Ni–C binary alloys [27].
Fig. 5. Representative stress–strain curves of bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid concentrations of 0 and 3.0 g/L. The strain was measured using a strain gauge with a maximum measured value of 5.0%. The elongation after fracture was obtained experimentally by comparing the gauge length before and after the tensile test. The inset image shows the actual specimen of the alloys electrodeposited using 3.0 g/L propionic acid after fracture.
Table 2 Mechanical properties of electrodeposited bulk nanocrystalline Fe–Ni alloys in the as-deposited state and after grain boundary relaxation by propionic acid addition and thermal treatments. Propionic acid (g/L)
Annealing at 200 1C
Hardness (GPa)
Strength (GPa)
Elongation (%)
0 3.0 0
– – Applied
4.0 7 0.02 5.0 7 0.04 5.0 7 0.01
1.63 7 0.02 1.737 0.03 1.75 7 0.03
12.7 7 1.4 10.7 7 0.6 4.2 7 0.4
propionic acid after the tensile fracture; here plastic deformation can be seen. A number of studies have reported that in their as-deposited or as-prepared state, nanocrystalline metals often contain nonequilibrium grain boundaries with excess dislocation, misfit regions, or excess free volume [28–30]. A low-temperature annealing process is also shown to release excess defects without any measurable change in grain size or texture; this is termed as grain boundary relaxation. In fact, Jang and Atzmon [29] suggested,
based on high resolution TEM observations, that grain boundaries evolve gradually during low temperature annealing from an initial discontinuous structure into more equilibrium structures. In addition, several studies reported that low-temperature treatments can increase hardness and tensile strength [31,32]. Grain boundary relaxation is expected to reduce the dislocation sources and result in higher hardness for the same or similar grain size [33]. As grain sizes reach nanometer range, the grain boundary state has a key role in the mechanical properties in addition to the grain sizes [34]. The results of mechanical measurements in this study show a 25% increase in the hardness of electrodeposited bulk nanocrystalline Fe–Ni alloys upon addition of propionic acid to the deposition bath, and the addition rarely produces a change in the grain sizes or Ni, S, and C contents of the electrodeposits. There is a probability that the addition of propionic acid results in grain boundary relaxation, even in the as-deposited state, without requiring additional thermal treatments. To explore the potency, additional three thick samples were electrodeposited using propionic acid concentrations of 0, 1.0, and 3.0 g/L, and all samples were annealed at 200 1C for a total of 2 h. Grain boundary relaxation occurs at approximately 400 1C or lower for Fe-based alloys [33,35]. XRD analysis and micro-Vickers hardness tests were also conducted at each interval. Fig. 6 shows the XRD patterns of the samples in the as-deposited state and after the 200 1C treatment. This shows that the thermal treatments applied in this study did not cause any obvious changes to the microstructure of the samples. The grain sizes remained unchanged after annealing. Hardness values are plotted against annealing time in Fig. 7. Thermal treatments resulted in an increase in the hardness, and the hardening behavior varied with the propionic acid concentration. The hardness of the nanocrystalline Fe–Ni alloys electrodeposited without propionic acid drastically increased from 4.3 GPa to 5.1 GPa, an increase of 20%. The alloys electrodeposited using 1.0 and 3.0 g/L propionic acid after annealing had a higher hardness in the as-deposited state with 10% and 4% increases in the hardness, respectively. Moreover, Rupert et al. [34] reported a 20% increase in the hardness for Ni–W alloys due to grain boundary relaxation. There is a slight strengthening of the grain boundary relaxation for the sample electrodeposited using propionic acid compared to the reported behavior and the sample electrodeposited without propionic acid. Moreover, the magnitude of the hardness plateau for the annealed alloys is comparable to that of the alloys electrodeposited using 3.0 g/L propionic acid in the asdeposited state. This agreement indicates that addition of propionic acid to the deposition bath can result in equilibrium structures in electrodeposited Fe–Ni alloys even in the as-deposited state,
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Fig. 6. XRD patterns for bulk nanocrystalline Fe–Ni alloys electrodeposited using (a) 0 and (b) 3.0 g/L propionic acid upon annealing at 200 1C for 2 h. P stands for the concentration of propionic acid in the deposition bath and d stands for the grain size calculated from XRD determination of the (111) peak width.
Fig. 7. Hardness versus annealing time for bulk nanocrystalline Fe–Ni alloys electrodeposited using 0, 1.0, and 3.0 g/L propionic acid for annealing temperatures at 200 1C. P stands for concentration of propionic acid in the deposition bath.
and the reduction excess grain boundary defects cause higher hardness. We applied annealing to bulk nanocrystalline Fe–Ni alloys electrodeposited without propionic acid and evaluated the tensile properties to compare the effect of grain boundary relaxation by thermal treatments and propionic acid addition on the tensile behavior. The thermal treatments resulted in an increase in the hardness to 5.0 GPa; this corresponded to the addition of 3.0 g/L propionic acid (Table 2). The representative stress–strain curves of the alloys electrodeposited without propionic acid upon the thermal treatments at 200 1C are shown in Fig. 8, and the results are given in Table 2 and Fig. 9. Fig. 9 shows that the thermal treatments increased the tensile strength to 1.76 GPa, and this value is comparable to that of the alloys electrodeposited using 3.0 g/L propionic acid. This indicates that the increases of the tensile strength for bulk nanocrystalline Fe–Ni alloys with propionic acid addition were also resulted from the reduction of excess grain boundary defects. On the other hand, the tensile strength of the electrodeposited alloys rises only by 6% with the addition of propionic acid, while the hardness rises by 25%. The difference of the strengthening effect would be caused by a different deformation mechanism for tensile and compression. The annealed bulk nanocrystalline Fe–Ni alloys exhibited lower tensile ductility than the alloys electrodeposited using propionic acid (Fig. 9). The Fe–Ni alloys after annealing showed a tensile ductility of 4%, while the alloys electrodeposited using 3.0 g/L propionic acid showed ductility of 11%. Impurity segregation is often detrimental to ductility. Grain boundary fracture on
Fig. 8. Representative tensile behaviors of bulk nanocrystalline Fe–Ni alloys electrodeposited using no propionic acid in the as-deposited state and after annealing at 200 1C. The strain was measured using a strain gauge with a maximum measured value of 5.0%. The thermal treatment was applied to increase the hardness to values that correspond with those of the alloys electrodeposited using propionic acid of 3.0 g/L in the as-deposited state.
Fig. 9. Comparison of the effect of grain boundary relaxation by thermal treatments and propionic acid addition on the tensile properties.
coarse-grained Fe–Ni alloys is caused by segregation of sulfur, which weakens the grain boundary cohesion [22,36]. Moreover, Fe–Ni alloys show more sulfur-induced embrittlement than
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Fe-based alloys and steels [37]. A very low sulfur concentration of 10 ppm is enough to cause ductility loss in the Fe–Ni alloys [38,39]. In addition, Klement et al. [40] and Wang et al. [32] investigated using EDS and electron energy-loss spectroscopy techniques the segregation of impurities in grain boundaries by annealing in electrodeposited nanocrystalline Ni. Both studies detected sulfur segregation in the grain boundaries on nanocrystalline Ni annealed at 200–250 1C. On the other hand, both studies did not detect any obvious segregation of carbon, which is the grain boundary cohesion enhancer, in the grain boundaries [22,36]. It is possible that the sulfur segregation happens by annealing for grain boundary relaxation in electrodeposited bulk nanocrystalline Fe–Ni alloys and results in the reduction of tensile ductility. In contrast, propionic acid addition for grain boundary relaxation is at low risk for segregation of sulfur in the grain boundaries, and it could increase the tensile strength while maintaining a high tensile ductility of 10%. 4. Conclusions 1. In electrodeposition for Fe–Ni alloys with an fcc structure, addition of propionic acid to the deposition bath slightly affected the C content of the electrodeposits compared with Fe–Ni alloys with a bcc structure. Moreover, the addition of propionic acid had no effect on the current efficiency of the deposition bath, grain sizes, or Ni or S contents of the electrodeposited alloys. 2. Addition of propionic acid to the deposition bath can significantly increase the hardness of electrodeposited nanocrystalline Fe–Ni alloys. An increase in the hardness of 25%, amounting to 1.0 GPa, was observed as the concentration of propionic acid increased to 3.0 g/L. The strengthening is much larger than expected for solid solution strengthening arising from octahedral-interstitial carbon for Ni–C binary alloys. 3. The results of tensile tests showed an enhanced tensile strength of 1.7 GPa in bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid compared to those electrodeposited without propionic acid. In addition to the high tensile strength, the bulk nanocrystalline Fe–Ni alloys electrodeposited using propionic acid exhibited a high tensile ductility of 10%. 4. Low temperature annealing at 200 1C can increase the hardness of Fe–Ni alloys deposited without propionic acid from 4.3 to 5.1 GPa, but the treatments rarely influence the hardness of the alloys deposited with propionic acid. The hardness values after annealing are comparable to that of alloys deposited with 3.0 g/L propionic acid in the as-deposited state. 5. The results of thermal treatments in this study and discussion based on the grain boundary relaxation strengthening indicate that the addition of propionic acid produced more equilibrium structures on the electrodeposited alloys. The relaxation of excess grain boundary defects by propionic acid addition could result in higher hardness and tensile strength, along with a high ductility of 10%, in electrodeposited bulk nanocrystalline Ni–Fe alloys.
Acknowledgments This study was supported by a Grant-in-Aid for Scientific Research from (C) (25390031) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan and a Grant-in-Aid for JSPS Fellows.
References [1] C. Cheung, F. Djuanda, U. Erb, G. Palumbo, Nanostructured Mater. 5 (1995) 513–523. [2] D.L. Grimmett, M. Schwartz, K. Nobe, J. Electrochem. Soc. 140 (1993) 973–979. [3] S.D. Leith, S. Ramli, D.T. Schwartz, J. Electrochem. Soc. 146 (1999) 1431–1435. [4] A. Sanaty-Zadeh, K. Raeissi, A. Saidi, J. Alloys Compd. 485 (2009) 402–407. [5] C. Rousse, P. Fricoteaux, J. Mater. Sci. 46 (2011) 6046–6053. [6] F. Czerwinski, Electrochim. Acta 44 (1998) 667–675. [7] H. Li, F. Ebrahimi, Mater. Sci. Eng. A 347 (2003) 93–101. [8] Y.M. Yeh, G.C. Tu, T.H. Fang, J. Alloys Compd. 372 (2004) 224–230. [9] H. Li, F. Ebrahimi, Acta Mater. 54 (2006) 2877–2886. [10] I. Matsui, T. Kawakatsu, Y. Takigawa, T. Uesugi, K. Higashi, Mater. Lett. 116 (2014) 71–74. [11] B. Srinivasarao, K. Oh-ishi, T. Ohkubo, K. Hono, Acta Mater. 57 (2009) 3277–3286. [12] R.K. Guduru, R.O. Scattergood, C.C. Koch, K.L. Murty, S. Guruswamy, M. K. McCarter, Scr. Mater. 54 (2006) 1879–1883. [13] V.G. Gavriljuk, V.N. Shivanyuk, B.D. Shanina, Acta Mater. 53 (2005) 5017–5024. [14] L. Cheng, A. Bö ttger, T.H. de Keijser, E.J. Mittemeijer, Scr. Metall. Mater. 24 (1990) 509–514. [15] C.P. Scott, J. Drillet, Scr. Mater. 56 (2007) 489–492. [16] D.J. Hepburn, D. Ferguson, S. Gardner, G.J. Ackland, Phys. Rev. B 88 (2013) 024115. [17] Z. Budrovic, H. Van Swygenhoven, P.M. Derlet, S. Van Petegem, B. Schmitt, Science 304 (2004) 273–276. [18] H. Van Swygenhoven, P.M. Derlet, Phys. Rev. B 64 (2001) 2241051–2241059. [19] J.W. Cahn, Y. Mishin, A. Suzuki, Acta Mater. 54 (2006) 4953–4975. [20] R. Wu, A.J. Freeman, G.B. Olson, Phys. Rev. B 53 (1996) 7504–7509. [21] R. Wu, A.J. Freeman, G.B. Olson, Science 265 (1994) 376–380. [22] M. Yamaguchi, Metall. Mater. Trans. A 42 (2011) 319–329. [23] Y. Fujiwara, T. Nagayama, A. Nakae, M. Izaki, H. Enomoto, E. Yamauchi, J. Electrochem. Soc. 143 (1996) 2584–2590. [24] M. Izaki, T. Omi, Metall. Mater. Trans. A 27 (1996) 483–486. [25] Y. Fujiwara, M. Izaki, H. Enomoto, T. Nagayama, E. Yamauchi, A. Nakae, J. Appl. Electrochem. 28 (1998) 855–862. [26] I. Matsui, Y. Takigawa, T. Uesugi, K. Higashi, Mater. Sci. Eng. A 578 (2013) 318–322. [27] I. Matsui, T. Uesugi, Y. Takigawa, K. Higashi, Acta Mater. 61 (2013) 3360–3369. [28] X.L. Wu, Y.T. Zhu, Appl. Phys. Lett. 89 (2006) 031922. [29] D. Jang, M. Atzmon, J. Appl. Phys. 99 (2006) 083504. [30] S. Ranganathan, R. Divakar, V.S. Raghunathan, Scr. Mater. 44 (2001) 1169–1174. [31] A.J. Detor, C.A. Schuh, J. Mater. Res. 22 (2007) 3233–3248. [32] Y.M. Wang, S. Cheng, Q.M. Wei, E. Ma, T.G. Nieh, A. Hamza, Scr. Mater. 51 (2004) 1023–1028. [33] H. Kotan, K.A. Darling, M. Saber, R.O. Scattergood, C.C. Koch, J. Mater. Sci. 48 (2013) 1–10. [34] T.J. Rupert, J.R. Trelewicz, C.A. Schuh, J. Mater. Res. 27 (2012) 1285–1294. [35] H. Kotan, M. Saber, C.C. Koch, R.O. Scattergood, Mater. Sci. Eng. A 552 (2012) 310–315. [36] M. Yamaguchi, M. Shiga, H. Kaburaki, J. Phys.: Condens. Matter 16 (2004) 3933–3956. [37] T. Tanaka, H. Sawada, ISIJ Int. 53 (2013) 1289–1291. [38] L. Ben Mostefa, G. Saindrenan, M.P. Solignac, J.P. Colin, Acta Metall. Mater. 39 (1991) 3111–3118. [39] M.T. Perrot-Simonetta, A. Kobylanski, J. Phys. IV 05 (1995) C7-323–C7-334. [40] U. Klement, U. Erb, A.M. El-Sherik, K.T. Aust, Mater. Sci. Eng. A 203 (1995) 177–186.