Available online at www.sciencedirect.com
ScienceDirect Procedia Materials Science 12 (2016) 95 – 99
6th New Methods of Damage and Failure Analysis of Structural Parts [MDFA]
Direct bonding of SUS304 stainless steel by metal salt generation bonding technique with formic acid Shinji Koyamaa,*, Tatsunori Tsunetob b
a Faculty of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan
Abstract In this study, the effect of the metal salt generation bonding technique on the strength of a direct-bonded SUS304 stainless steel interface was investigated. SUS304 stainless steel surfaces were modified by boiling in 50% formic acid, and direct bonding was performed at a bonding temperature of 1023-1123 K under a pressure of 147 N (for a bonding time of 900 s). After direct bonding, the specimens were subjected to the peel test for evaluating their strength. As a result of the surface modification, bonded joints were obtained at bonding temperature of 30 K lower than that required for the unmodified surfaces, and the peel strength was comparable to that of the maximum load. On the basis of the experimental results, it was established that metal salt generation processing is effective for removing oxide films on SUS304 stainless steel. © TheAuthors. Authors.Published Published Elsevier © 2014 2016 The by by Elsevier Ltd.Ltd. This is an open access article under the CC BY-NC-ND license Selection and peer-review under responsibility of the VŠB - Technical University of Ostrava, Faculty of Metallurgy and (http://creativecommons.org/licenses/by-nc-nd/4.0/). Materials Engineering. Selection and peer-review under responsibility of the VŠB - Technical University of Ostrava,Faculty of Metallurgy and Materials Engineering Keywords: Metal salt generation bonding; Fracture; Bonding strength; SUS304; Forimic acid
1. Introduction In recent years, the demands for energy-efficient devices are increasing as societies around the world are becoming more environmentally conscious. Efforts to address this demand are being made in various fields including the medical equipment (automated bio chemical analyzer and artificial heart-lung machine); Furushima et al (2013). Therefore, SUS304 stainless steel which is excellent in corrosion resistance, toughness and workability is
* Corresponding author. Tel.: +81-277-30-1545; fax: +81-277-30-1545. E-mail address:
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2211-8128 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and peer-review under responsibility of the VŠB - Technical University of Ostrava,Faculty of Metallurgy and Materials Engineering doi:10.1016/j.mspro.2016.03.017
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widely used for manufacturing medical devices; Inoue et al (2011). We propose assembling medical devices using solid-state bonding rather than the fusion bonding method; this method is suitable for miniaturized medical equipment; Onoki et al (2009), Jing et al (2014), Koyama et al (2014). Earlier research showed that surface modification decreased the bonding temperature required to obtain a high-bond-strength joint in the solid-state bonding of Cu/Sn; Koyama et al (2010). In this investigation, we aimed to obtain a deeper understanding of the effect of metal salt generation bonding process on the performance of a solid-state bonded joint of SUS304 stainless steel by SEM observation of interfacial microstructure and fractured surfaces. 2. Experimental details As shown in Fig. 1, the specimen used in this study comprised a 15 × 15 × 5 mm3 plate (Table 1) and a 5 × 100 × 0.178 mm3 sheet (Table 2). Before surface modification, the bonding surface of plate was polished with a #4000 emery paper, and the bonding surface of sheet was finished by buffing. After finishing, the bonding surface was ultrasonically cleaned with acetone for 1800 s.
Table 1. Chemical composition of SUS304 sheet used in this study Elements
C
Si
Mn
P
S
Ni
Cr
Mass%
0.05
0.39
1.10
0.03
0.004
8.03
18.01
Table 2. Chemical composition of SUS304 sheet used in this study Elements
C
Si
Mn
P
S
Ni
Cr
Mass%
0.05
0.41
1.10
0.027
0.002
8.03
18.05
The surface modification with formic acid was carried out by boiling the surfaces in formic acid (50%) for optimized times (660 s) at about 373 K. To identify the compound formed on the surface after surface modification, grazing-angle incidence reflection-absorption infrared (GIRAS-IR) spectroscopy was employed to obtain IR spectra at a nanometer-scale depth from the modified nickel surface. The spectra were obtained by an FT-IR spectrometer (Thermo Fisher Inc. Magna-750) equipped with an MCT detector using a single reflection accessory (Harrick Inc. Seagull) at an incident angle of 80° using a mercury-cadmium-telluride detector. An Au-coated mirror surface was used as the reflection reference and measurements were carried out at a wavenumber resolution of 8 cm-1. After surface modification, the specimen was set up in N2 flowed chamber within 180 s, omit to avoid oxidation or other changes induced by moisture adsorption at the surfaces. The direct bonding was carried out at bonding temperatures (T) ranging from 1023 to 1123 K. The bonding pressure and time were fixed at 147 N and 1800 s, respectively: the bonding pressure was applied for the specified bonding time, before heating the sample. After direct bonding, the bond strength was evaluated using the peel test. This test was performed using an Instron 5567 universal testing machine at room temperature and with a displacement rate of 0.17 mm/s.
Fig. 1. Schematic illustrations of SUS304 sheet and plate specimen used in this study
Shinji Koyama and Tatsunori Tsuneto / Procedia Materials Science 12 (2016) 95 – 99
3. Results and Discussion 3.1. Effect of metal salt generation processing on bond strength To examine the influence of the metal salt generation processing time on the peel strength of the joint, the direct bonding was carried out at modification time t from 180 to 1200 s and the bonding temperature T was fixed at 1073 K. The relationship between the modification time and the peel strength of the joints is shown in Fig. 2. The joint with the highest peel strength was obtained when the metal salt generation processing time was 660 s. This tendency suggests that when the metal salt generation processing time is short, the oxide film is not substituted; and when the time is long, an excessive quantity of the compound is formed. For these reasons, it was determined that the best modification time was 660 s. Fig. 3 shows the relationship between the bonding temperature and the peel strength of the modified joint. To illustrate the effect of metal salt generation processing, the same relationship is also shown for an unmodified joint. As shown in Fig. 3, the peel strength increased with the bonding temperature, irrespective of the specific metal salt generation processing. When the surface was modified with formic acid, the peel strength was nearly about 600 N at a bonding temperature of approximately 30 K lower than that of the unmodified joint. At a bonding temperature of 1073 K or more, the peel strength was higher about 300 N than that of the unmodified joint. Therefore, it is inferred that the effect of metal salt generation processing were exerted at about 1073 K. Moreover, in the case of the surface were modified and a bonding temperature of 1123 K, fractures of the base metal a part in the joint occurred. In addition, all the specimens broke at the bond interface.
Fig. 2. Relationship between peel strength and modification time
Fig. 3. Effect of surface modification on relationship between peel strength and bonding temperature
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3.2. Fracture surface observation To examine the factors determining fracture at the bond interface, the area of the fractured surface was observed with SEM. As shown in Fig. 4, when the surface was not modified and the bonding temperature of 1023 K, substances are not found to adhere to either the surface. With a rise in bonding temperature, substances came to be observed in a part in the fractured surfaces. When the surface was modified and the bonding temperature of 1023 K, the fractured surface started to show ductile fracture characteristics, although it was not observed when the surface modification was not applied. Thus, it is hypothesized that high-peel-strength joints were obtained at a lower bonding temperature with metal salt generation processing because the contact are between SUS304 stainless steel was increased. From these results, it can be inferred that the joints bonded at lower temperature than the unmodified joints had higher peel strengths because the removal of the oxide film between the bonding surfaces enables a close contact between the atomic planes of SUS304 steel.
Fig. 4. SEM micrographs of fracture surfaces of joints after peel test
3.3. Chemical analysis of reaction product It is thought that SUS304 stainless steel exposed to the atmosphere are immediately covered with an oxide film. Fig. 5 shows the FT-IR analysis of the direct bonding surface of SUS304 stainless steel before and after metal salt generation processing with formic acid. The results reveal that, in comparison with the unmodified surface, the modified surface contained lower amounts of oxides, as well as a higher amount of metallic atomic plane. Moreover, the IR spectrum of modified sample shows IR absorption bands characteristic to carboxylate at 1610 cm-1, which indicates the existence of metal salt at the surface. It is also well known that nickel (II) formate is formed by boiling or exposing these oxide film and base metal with formic acid; Kusafuka et al (2002). The GIRAS-IR spectrum is shown in Fig. 6. Whereas the IR spectrum of the unmodified sample shows only spectra characteristic to siloxane compounds as contaminations during the polishing process, the IR spectrum of modified sample shows IR absorption bands characteristic to carboxylate at 1350 and 1650 cm-1, which indicates the existence of nickel (II) formate at the surface. It is known that at about 403 K, nickel (II) formate undergoes an endothermic decomposition reaction, as shown by following formula, to generate metallic nickel: Ni(HCOO)2 → Ni + H2↑+ CO2↑. It is therefore thought that a high-peel-strength joint was obtained at a lower bonding temperature with metal salt generation process because metal salt such as nickel (II) formate at the bond interface underwent a decomposition reaction during bonding process.
Shinji Koyama and Tatsunori Tsuneto / Procedia Materials Science 12 (2016) 95 – 99
Fig. 5. FT-IR spectra of the SUS304 surface
Fig. 6. FT-IR spectra of the Ni surface
4. Conclusions The investigation into direct bonding of SUS304 stainless steel by metal salt generation bonding technique by using the formic acid has been found as reliable and the following conclusions can be drawn from the study: The peel strength approached about the biggest strength when the metal salt generation processing was applied (600 N) at a bonding temperature approximately 30 K or more lower than that for the unmodified joint. The oxide layer on the SUS304 surface can be reduced by metal salt generation processing and the thermolysis of metal salt promotes intimate contact between bonding surfaces. The increased surface area of the metallic surface contributes to increase of peel strength. Acknowledgements This work was supported by Grant-in-Aid for Young Scientists (B) (26820124) from Japan Society for the Promotion of Science (JSPS). References Furushima, T., Nguyen, H., Manabe, K., Sasaki, O., 2013. Development of semi-dieless metal bellows forming process. Journal of Materials Processing Technology 213, 1406-1411. Inoue, A., Takeuchi, A., 2011. Recent development and application products of bulk glassy alloys. Acta Materialia 59, 2243-2267. Jing, Y., Qin, Y., Zang, X., Li, Y., 2014. The bonding properties and interfacial morphologies of clad plate prepared by multiple passes hot rolling in a protective atmosphere. Journal of Materials Processing Technology 214, 1686-1695. Koyama, S., Aoki, Y., Shohji, I., 2010. Effect of formic acid surface modification on bond strength of solid-state bonded interface of tin and copper. Materials Transactions 51, 1759-1763. Kusafuka, K., Noguchi, H., Onda, K., Kubota, J., Domen, K., Hirose, C., Wada, A., 2002. Time-resolved study of formate on Ni(111) by picosecond SFG spectroscopy. Surface Science 502-503, 313-318. Matsubara, K., Koyama, S., Nagata, H., Suda, Y., Shohji, I., 2014. Solid state bonding of Al alloy/SUS304 by metal salt generation bonding technique with acetic acid. Advanced Materials Reserch 922, 491-496. Onoki, T., Wang, X., Zhu, S., Sugiyama, N., Hoshikawa, Y., Akao, M., Matsushita, N., Nakahira, A., Yasuda, E., Yoshimura, M., Inoue, A., 2009. Effects of growing integrated layer [GIL] formation on bonding behavior between hydroxyapatite ceramics and Ti-based bulk metallic glasses via hydrothermal hot-pressing
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