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Sinter bonding of AISI 4340 and WC-Co using Ni interlayer by inserted powder injection molding
Ceramics International 45 (2019) 22331–22335
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Sinter bonding of AISI 4340 and WC-Co using Ni interlayer by inserted powder injection molding
T
Harun Koçaka, Mehmet Subaşıb,*, Çetin Karataşc a
Department of Aircraft Technology, TUSAŞ-Kazan Vocational School, Gazi Universty, Ankara, Turkey Department of Machine and Metal Technology, Technical Sciences Vocational School, Gazi University, Ankara, Turkey c Department of Manufacturing Engineering, Faculty of Technology, Gazi University, Ankara, Turkey b
A R T I C LE I N FO
A B S T R A C T
Keywords: Sinter bonding Interlayer WC-Co Inserted powder injection molding
An inserted powder injection molding (IPIM) method has been developed to overcome the size limitation (< 10 mm) in the part production with powder injection molding process. In this method, the part called insert is placed into the mould and the feedstock is injected onto it and then the part is sintered. With this method it is possible to produce parts from different materials by using inserts. In this study, bonding of WC-Co feedstock and AISI 4340 insert during the sintering process was investigated by IPIM method using Ni interlayer. In EDS analyses, the most diffused element was determined as W depending on the concentration difference. When the intermediate zone was examined, it was observed that the Ni interlayer was infiltrated along 10 mm towards the WC-Co side. Meanwhile, on the AISI 4340 insert side, a diffusion zone which is 35 μm wide was determined. As the shear strength of the intermediate zone is increased, Ni interlayer thickness and sintering time is increased. The highest shear strength came out to be 266.5 MPa in the 240 min sintering time by using 100 μm Ni interlayer.
1. Introduction Powder Injection Molding (PIM) method is more economical than Powder Metallurgy (PM) methods for mass production and geometric precision. Besides it has more advantageous in part designing with respect to Powder Metallurgy [1–3]. However, this method is limited by the production of bigger parts. For this reason the inserted powder injection molding (IPIM) method has been developed [4]. In this method, the part called insert is placed into the mould and the feedstock is injected onto it. It is possible to produce functional parts consisting of different materials supposing that the bonding is obtained during sintering [4,5]. However, when parts are produced by using different materials such as metal insert and ceramic feedstock, physical and chemical characteristics of the materials significantly affect the desired strength value in the inter section [6,7]. In literature, a number of researches was made on bonding of WCCo and steel by different methods like diffusion welding and soldering [8–10]. In some studies about this subject, it is emphasized that diffusion is better and shear strength is increased in the intermediate region when an interlayer is used while bonding WC-Co and steel [11,12]. Barrena et al. (2010) [10] obtained 620 MPa shear strength by using
Ni/Cu interlayer in bonding of WC-Co and 90MnCrV8 steel, Jiang et al. (2016) [13] obtained 366 MPa shear strength by using Ag–Cu–Zn–Mn–Ni alloy in bonding WC-Co and 35CrMo steel, Guo et al. (2016) [14] obtained 293 MPa shear strength by using Ni interlayer in bonding WC-Co and 40 Cr steel, Feng et al. (2013) [15] obtained 195 MPa shear strength by using Ni interlayer in bonding WC-Co and 410ss steel and, Chen et al. (2012) [16] obtained 154 MPa shear strength by using Ni/Cu–Zn/Ni interlayer in bonding WC-Co steel. Simchi and Petzoldt, in their study [17], investigated the sintering behaviors of the parts produced by mounting with powder injection molding method from the WC-Co and 316L feedstocks. In their study, it is stated that the different stresses between the materials caused interfacial delamination, the liquid phase formed at 1220 °C due to diffusion of C and Co in the contact regions of the materials and the dimensional stability is affected from liquid phase formed. Besides, in the study, there is no data on shear strength regarding bonding. In the literature, part production by IPIM method is limited. In this study, parts whose inner side was AISI 4340 and outer side was WC-Co were prepared. Nickel interlayer was used for the full bonding of the inner and outer sides. The effect of nickel interlayer bonding process between inner and outer sides was investigated. As a result of
* Corresponding author. Technical Sciences Vocational School of Higher Education, Gazi University, Ankara, 06374, Turkey. Tel.:0 312 354 84 01, Fax.: 0 312 354 38 35 E-mail address: [email protected] (M. Subaşı).
https://doi.org/10.1016/j.ceramint.2019.07.261 Received 15 May 2019; Received in revised form 10 July 2019; Accepted 22 July 2019 Available online 23 July 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Ceramics International 45 (2019) 22331–22335
H. Koçak, et al.
Fig. 2, diffusion bond between outside and inside parts was achieved during the sintering process. It is thought that with the use of steel in the inner region and WC-Co in the outer region of the part will make the it qualified and optional in terms of both toughness and wear of the part.
Table 1 Technical characteristics of feedstock. Powder shape
Density (g/cm3)
Powder size (μm)
Complex shaped
8.06
D10 0.15
D50 0.28
D90 0.52
3.1. Bonding at WC- Co/Ni and Ni/4340 interfaces experiments at 1250 °C with three different sintering times (120-240360 min), the effect of nickel interlayer thickness (25, 50, 100 μm) on shear strength was investigated. 2. Materials and methods 2.1. Preparation of inserts and application of interlayer Inner side of the samples consisted of AISI 4340 steel insert whereas the outer side was WC-Co (9%) feedstock. The feedstock was supplied from Ryer firm availably. Technical attributes of WC- 9% Co feedstock are given in Table 1. Chemical compositions of insert materials and feedstock are given in Table 2. Before the injection process, the cylindrical inserts prepared from AISI 4340 steel material were coated with 25–50-100 μm Ni of ± 3 μm tolerance through electrolytic coating for the application of interlayer. Coating conditions are given in Table 3. After coating, the coating thickness was measured from the diameter surface using maXXi 5 X-Ray measuring device. 2.2. Inserted powder injection molding Injection process was made at the ARBURG Allrounder 220 S injection molding machine. Nickel coated inserts were placed into the mould and feedstock was injected onto them (Fig. 1). Optimum injection parameters were determined according to the producer's advice and type of product. Parameters used in the injection process are given in Table 4.
In order to understand how the bonding process took place at the WC-Co/Ni and Ni/4340 steel interfaces, the microstructure of the intermediate zone was examined. In the microstructure images, it was observed that WC-Co and AISI 4340 steel was successfully bonded and a gray color diffusion zone of 35 μm wide was determined at the Ni/4340 steel interface (Fig. 3a). In this study sintering temperature was 1250 °C and atomic diameters of nickel (0.125 nm) and iron (0.124 nm) elements were close to each other [18]. Therefore, the conditions are quite suitable for diffusion at the Ni/4340 steel interface. Zhong et al. (2009), in their study about bonding of tungsten and stainless steel with Ni interlayer, determined that nickel and iron could make solid solution owing to diffusion of Ni and Fe atoms correspondingly at high temperature [11]. In Fig. 3a, the same bonding process at Ni/4340 steel interface with diffusion is also seen in our study. When the WC-Co/Ni interface was examined, an infiltration of Ni interlayer (during sintering) was detected towards 10 μm inside of the WC-Co (Fig. 3b). Vaidya et al.(1998) [19], in their study, stated that the melting temperature of the Fe–Ni–Co–W–C phase was 1200–1300 °C depending on composition. It is thought that a Ni dominant Ni–Fe–Co–W–C liquid phase was created at the WC-Co/Ni interface with the diffusion of iron towards WC-Co side at 1250 °C sintering temperature. Ni dominant liquid phase was infiltrated into the WC powders by the effect of capillary pressure into the injected zone. Consequently the possible defects at the WC-Co/Ni interface decreased and bonding strength increased due to interlocking at the interface. 3.2. Effect of interlayer thickness and shear strength of intermediate zone
2.3. Debinding and sintering Samples were kept in ethanol at 60 °C for 48 h for debinding and after they were dried in a furnace at 60 °C. Following the debinding processing, the samples were sintered at 1250 °C under the control atmosphere (95 %N2 and 5% H2) for 120-240-360 min durations. In this study, heating rate is 5 °C/min in sintering process. 2.4. Mechanical tests and analyses Shear tests were carried out in accordance with TS EN ISO 6892-1 standard by using Instron testing device of 50 kN loading capacity at 1 mm/min constant speed. After sintering, micro hardness (HV0.2) measurements were made in 0.2 mm intervals and the hardness profile of the intermediate zone was obtained. The image examinations were made with the LEICA light microscope, and EDS analyses were made with JEOL JSM-6060LV Scanning Electron Microscope (SEM). 3. Results and discussion In this study, by using Ni interlayer, samples whose outer sides were WC-Co and the inner sides were AISI 4340 steel (Fig. 2) were produced by Inserted Powder Injection molding method. In the sample shown in
In the tests three Ni interlayers in different thicknesses (25-50100 μm) was used. Better results were obtained for shear strength and micro structure by using 100 μm interlayer. Micro structure of the intermediate zone became more regular as the thickness of interlayer increased. In Fig. 4a, it was observed that there was no defect in the intermediate zone and the interlayer thickness increased from 100 μm to approximately 160 μm after sintering. In Fig. 4b, it was seen that gaps were created in the middle of 50 μm interlayer and in Fig. 4c both greater gaps and cracks were found in the 25 μm interlayer. In bonding process of different materials such as metal and ceramic, thermal expansion difference between materials causes residual stresses while the sample is cooling. These residual stresses results in damages like cracking and separations in the intermediate zone. When an interlayer is used between metal and ceramic material, the plastic deformation formed in the interlayer decreases the residual stresses and a stronger bonding process is obtained. Vaidya et al.(1998) reported that when the intermediate layer thickness increases, the thermal expansion difference is better tolerated due to presence of high volume of intermediate layer material for plastic deformation, and both residual stresses and errors in the intermediate zone are reduced [19]. In the other studies in literature, it is also stated that residual stresses and defects in the intermediate zone decrease as the thickness of interlayer
Table 2 Chemical composition of the materials.
AISI 4340 WC-Co
C
Si
Mn
Cr
Mo
Ni
V
W
Co
P
S
Fe
0.39 5.54
0.22 –
0.67 –
0.78 0.01
0.24 0.01
1.74 0.01
– –
– bal.
– 8.94
0.025 –
0.025 –
bal. 0.01
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Table 3 Conditions of electrolytic coating. Anode
Bath temperature
Electrolytic Nickel
50–60 °C
Voltage
Current density
2.5–3 V
2
4A/dm
Waiting time 1 μm for 2 min
Fig. 1. Inserted powder ınjection molding (IPIM) process. Table 4 Powder injection molding parameters. Injection temperature
Injection pressure
Holding pressure
Injection rate
Mould temperature
200 °C
280 bar
80 bar
10 ccm/s
60 °C
Fig. 2. The part produced by the IPIM method (after sintering at 1250 °C).
increases [20,21]. In our study the same results were obtained too. Gaps in the inner side of interlayer and cracks near the interface were observed as the interlayer thickness decreased. Defects at the intermediate zone decreased as the interlayer thickness increased. In the tests, the highest value of shear strength was obtained as 266.5 MPa. Guo et al.(2016) [14] obtained 293 MPa shear strength in the bonding process of WC-Co 40Cr steel using Ni interlayer, Feng et al. (2013) [15] obtained 195 MPa in the bonding process of WC-Co and 410ss steel by using Ni interlayer again, Chen et al.(2012) [16] obtained 154 MPa in the bonding process of WC-Co 3Cr13 steel using Ni/ Cu–Zn/Ni interlayer. In this study, the bonding process was made during sintering without vacuum. In spite of the fact that no pressure was applied as in the diffusion welding process, shear strength value is higher than a number of studies in literature. The highest shear strength value was obtained by using 100 μm Ni interlayer. Increasing interlayer thickness increased the shear strength. Similar to literature, increasing interlayer thickness decreased the defects in the intermediate zone (Fig. 4) and consequently the shear strength increased (Fig. 5). It is observed that sintering time was also effective on the shear strength. When the graph is examined in Fig. 5, it is seen that shear strength increases as the sintering time increases. In Fig. 3, it is also seen that Ni interlayer diffuses towards the steel side and infiltrates towards the WC-Co side. Kurt et al. (2007), in their study stated that as the duration of process increased shear strength also increased with the increasing diffusion between the bonded materials [22]. Jadoon et al. (2004) [23] indicated that in bonding ceramic and metallic materials, a closer contact was provided at the interface with the infiltration of interlayer towards the ceramic side and then a mechanical locking
Fig. 3. Micro structure of interfaces (1250 °C, 240 min, 100 μm Ni).
occurred, therefore the shear strength increased. In this study, as the sintering time increased diffusion and infiltration also increased and consequently the shear strength value raised (Fig. 5). In the literature, generally, the temperature in the process of diffusion bonding of WC and steel ranges from 900 °C to 1100 °C and the time ranges from about 10 min to 60 min. In this study, since the experiments were performed at 1250 °C and for 120, 240, 360 min periods, diffusion and infiltration increased in the intermediate region of Ni interlayer. Thus, both the errors in the intermediate region decreased and the shear strength of the intermediate region was provided to be higher than the literature. 3.3. Element transitions in the 4340/Ni/WC-Co intermediate zone It is stated that in the spectral analysis report of 4340 material taken from the firm, the Fe and Ni percentages were 95.91% and 1.74% respectively and there was no W and Co (Table 2). Following sintering process, EDS analyses were made on 10 points in the intermediate zone and the graph in Fig. 6 was obtained from the results. After sintering, it was observed that in the area of 4340 insert where the EDS analysis was made, Fe amount dropped to 74.2% and the ratio of diffused W and Co from WC-Co towards the insert is 13.7% and 4.41%, respectively. But the Ni amount in the 4340 insert didn't change significantly. Ni amount diffused from Ni interlayer towards WC-Co side was 1.82% averagely.
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Fig. 4. Effect of interlayer thickness.
Fig. 7. Hardness profile of intermediate zone (1250 °C, 240 min, 100 μm Ni).
3.4. Hardness profile of intermediate zone Fig. 5. Effect of sintering time and interlayer thickness on shear strength (1250 °C).
Fig. 6. Element concentration profile at the intermediate zone (%), (1250 °C, 240 min).
In the different studies of literature made for bonding WC-Co and steel with diffusion welding process, temperature was in the interval of 850–1100 °C and remarkable results were obtained in terms of both diffusion and strength by using Ni [10,14,16]. Because WC-Co and 4340 steel are bonded during sintering, the temperature is higher than studies in the literature and this allows sufficient element diffusion for bonding. In the EDS analysis, W transition is more than the other elements. Besides, although the atomic diameter of nickel was smaller, cobalt diffused into the insert more than nickel. Both of them can be explained with the concentration difference. In the diffusion mechanism, when the difference of element amount between two materials increases, the rate of element transition between materials also increases due to high concentration gradient [24]. W was diffused more than other elements to 4340 insert due to high concentration gradient. Besides diffusion ratio of cobalt was much more than nickel due to 9% (by weight) Co on the WC-Co side.
Hardness profile of intermediate zone is given in Fig. 7. According to this profile, the hardness of the insert was measured as 374–400 HV near the intermediate zone. However the hardness of the insert center was measured as 305 HV. Hardness of the injected zone was determined between 450 and 1383 HV (Fig. 7). After 0.8 mm from the intermediate zone, the hardness of WC-Co was found to be around 1400 HV without much change. Hardness of AISI 4340 insert was higher at the points close to intermediate zone but hardness of WC-Co was lower. This is because of the element diffusion between AISI 4340 insert and WC-Co during sintering and must be evaluated with EDS analysis. AISI 4340 insert contains 1.74% Ni. From the EDS analysis, it is seen that a diffusion of 13.7% W, 4.41% Co to 4340 insert and 1.22% Fe, 1.7% Ni to WC-Co side. In some studies on diffusion welding method, it is stated that W, Ni and Co diffused to steel side, creating an intermetallic compound and solid solution in the diffusion zone and consequently hardness changes at the points close to intermediate zone [10,11]. As a result, whereas W and Co (diffused to insert) increased the hardness of insert at the points close to intermediate zone and Fe and Ni (diffused to WC-Co side) caused a decrease in the hardness of WC-Co.
4. Conclusions With Inserted Powder Injection Molding (IPIM) method AISI 4340 steel insert and WC-Co were successfully bonded during sintering process. It was found that there is a diffusion zone of approximately 35 μm at the Ni/4340 interface and an infiltration of the Ni interlayer into WCCo with a depth of 10 μm. It was found that after sintering, the interlayer, which was 100 μm, increased to approximately 160 μm. It was found that gaps formed in the middle part of the 50 μm interlayer. It was found that both larger gaps and cracks at 25 μm interlayer thickness. As the thickness of the interlayer increased, the microstructure of the intermediate zone became more regular. The highest shear strength value was obtained at 100 μm Ni thickness. The highest shear strength value (266.5 MPa) in AISI 4340 steel insert and WC-Co interface was obtained at 100 μm Ni thickness.
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As the sintering time and the thickness of the interlayer increase, the shear strength generally increases. The highest shear strength was obtained in samples sintered at 1250 °C and for 240 min. Since the difference in W concentration was higher than the other elements, there was 13.7% diffusion rate in the insert with WC-Co in samples sintered at 1250 °C and for 240 min. W and Co diffused to the insert increased the hardness of insert in the region near the intermediate zone. Fe and Ni diffused to the WC-Co side caused a decrease in the hardness of WC-Co. While hardness of the insert in the regions close to the intermediate zone of the sintered samples at 1250C for 240 min is between 374 and 400 HV, hardness average in the parts close to the center of insert is 305 HV. The hardness of the injected area is 1383 HV utmost. The results of research can be used in all applications where toughness of the inner part and abrasion resistance of the outer part are desired high. These results can be used, for example, in the production of cutting tools. Acknowledgement This research was sponsored by the Scientific and Technological Research Council of Turkey (TÜBITAK), Project No: 115M437 and Gazi University Research Funds, Project No: 07/2016-21. The authors would like to express their sincere appreciation to TÜBITAK organization and Gazi University for their financial supports. References [1] Z. Baojun, Q. Xuanhui, T. Ying, Powder injection molding of WC–8%Co tungsten cemented carbide, Int. J. Refract. Metals Hard Mater. 20 (2002) 389–394. [2] A. Safarian, M. Subaşı, Ç. Karataş, Reducing debinding time in thick components fabricated by powder injection molding, Int. J. Mater. Res. 106 (2015) 527–531. [3] Ç. Karataş, S. Sarıtaş, Toz enjeksiyonla kalıplama: bir ileri teknoloji imalat metodu (Turkish), Journal of the Faculty of Engineering and Architecture of Gazi University 13 (1998) 193–228. [4] A. Safarian, M. Subaşı, Ç. Karataş, The effect of sintering parameters on diffusion bonding of 316L stainless steel in inserted metal injection molding, Int. J. Adv. Manuf. Technol. 89 (2017) 2165–2173. [5] H. Koçak, K. Samet, O. Yılmaz, Ç. Karataş, Investigation of composite part production from WC-Co/HSS using nickel interlayer by inserted powder injection molding method, Gazi University Science Journal: PART:C Design and Technology 6 (2018) 374–384. [6] A. Passerone, M.L. Muolo, Metal-ceramic interfaces: wetting and joining processes, Int. J. Mater. Prod. Technol. 20 (2004) 420–439.
[7] M. Subaşı, H. Koçak, Ç. Karataş, The investigation of effect on shear strength of nickel interlayer in inserted powder injection moulding, in: A. KURT (Ed.), 5th International Conference on Welding Technologies and Exhibition (ICWET’18) Sarajevo-Bosnia and Herzegovina, 2018, pp. 100–106. [8] M. Atabaki, Recent progress in joining of ceramic powder metallurgy products to metals, Association of Metall. Engineers of Serbia 16 (2010) 255–268. [9] R.M.d. Nascimento, A.E. Martinelli, A.J.A. Buschinelli, Review Article: recent advances in metal-ceramic brazing, Cerâmica 49 (2003) 178–198. [10] M.I. Barrena, J.M. Gómez de Salazar, L. Matesanz, Interfacial microstructure and mechanical strength of WC–Co/90MnCrV8 cold work tool steel diffusion bonded joint with Cu/Ni electroplated interlayer, Mater. Des. 31 (2010) 3389–3394. [11] Z. Zhong, T. Hinoki, A. Kohyama, Effect of holding time on the microstructure and strength of tungsten/ferritic steel joints diffusion bonded with a nickel interlayer, Mater. Sci. Eng. A 518 (2009) 167–173. [12] J.X. Zhang, R.S. Chandel, Y.Z. Chen, H.P. Seow, Effect of residual stress on the strength of an alumina–steel joint by partial transient liquid phase (PTLP) brazing, J. Mater. Process. Technol. 122 (2002) 220–225. [13] C. Jiang, H. Chen, Q. Wang, Y. Li, Effect of brazing temperature and holding time on joint properties of induction brazed WC-Co/carbon steel using Ag-based alloy, J. Mater. Process. Technol. 229 (2016) 562–569. [14] Y. Guo, Y. Wang, B. Gao, Z. Shi, Z. Yuan, Rapid diffusion bonding of WC-Co cemented carbide to 40Cr steel with Ni interlayer: effect of surface roughness and interlayer thickness, Ceram. Int. 42 (2016) 16729–16737. [15] K. Feng, H. Chen, J. Xiong, Z. Guo, Investigation on diffusion bonding of functionally graded WC–Co/Ni composite and stainless steel, Mater. Des. 46 (2013) 622–626. [16] H. Chen, K. Feng, S. Wei, J. Xiong, Z. Guo, H. Wang, Microstructure and properties of WC–Co/3Cr13 joints brazed using Ni electroplated interlayer, Int. J. Refract. Metals Hard Mater. 33 (2012) 70–74. [17] A. Simchi, F. Petzoldt, Cosintering of powder injection molding parts made from ultrafine WC-Co and 316L stainless steel powders for fabrication of novel composite structures, Metall. Mater. Trans. A 41 (2009) 233. [18] W.D. Callister, Materials Science and Engineering, John Wiley & Sons, Inc., New York, 2007. [19] R.U. Vaidya, P. Rangaswamy, M.A.M. Bourke, D.P. Butt, Measurement of bulk residual stresses in molybdenum disilicide/stainless steel joints using neutron scattering, Acta Mater. 46 (1998) 2047–2061. [20] W.-B. Lee, B.D. Kwon, S.B. Jung, Effect of bonding time on joint properties of vacuum brazed WC – Co hard metal/carbon steel using stacked Cu and Ni alloy as insert metal AU - Lee, W.-B, Materials Science and Technology 20 (2004) 1474–1478. [21] M.I. Barrena, J.M. Gómez de Salazar, N. Merino, L. Matesanz, Characterization of WC–Co/Ti6Al4V diffusion bonding joints using Ag as interlayer, Mater. Char. 59 (2008) 1407–1411. [22] B. Kurt, N. Orhan, A. Hasçalık, Effect of high heating and cooling rate on interface of diffusion bonded gray cast iron to medium carbon steel, Mater. Des. 28 (2007) 2229–2233. [23] A.K. Jadoon, B. Ralph, P.R. Hornsby, Metal to ceramic joining via a metallic interlayer bonding technique, J. Mater. Process. Technol. 152 (2004) 257–265. [24] A. Kurt, I. Uygur, H. Ates, Effects of temperature on the weldability of powder metal parts joined by diffusion welding, Mater. Sci. Forum 546–549 (2007) 667–670.
22335
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Sinter bonding of AISI 4340 and WC-Co using Ni interlayer by inserted powder injection molding
T
Harun Koçaka, Mehmet Subaşıb,*, Çetin Karataşc a
Department of Aircraft Technology, TUSAŞ-Kazan Vocational School, Gazi Universty, Ankara, Turkey Department of Machine and Metal Technology, Technical Sciences Vocational School, Gazi University, Ankara, Turkey c Department of Manufacturing Engineering, Faculty of Technology, Gazi University, Ankara, Turkey b
A R T I C LE I N FO
A B S T R A C T
Keywords: Sinter bonding Interlayer WC-Co Inserted powder injection molding
An inserted powder injection molding (IPIM) method has been developed to overcome the size limitation (< 10 mm) in the part production with powder injection molding process. In this method, the part called insert is placed into the mould and the feedstock is injected onto it and then the part is sintered. With this method it is possible to produce parts from different materials by using inserts. In this study, bonding of WC-Co feedstock and AISI 4340 insert during the sintering process was investigated by IPIM method using Ni interlayer. In EDS analyses, the most diffused element was determined as W depending on the concentration difference. When the intermediate zone was examined, it was observed that the Ni interlayer was infiltrated along 10 mm towards the WC-Co side. Meanwhile, on the AISI 4340 insert side, a diffusion zone which is 35 μm wide was determined. As the shear strength of the intermediate zone is increased, Ni interlayer thickness and sintering time is increased. The highest shear strength came out to be 266.5 MPa in the 240 min sintering time by using 100 μm Ni interlayer.
1. Introduction Powder Injection Molding (PIM) method is more economical than Powder Metallurgy (PM) methods for mass production and geometric precision. Besides it has more advantageous in part designing with respect to Powder Metallurgy [1–3]. However, this method is limited by the production of bigger parts. For this reason the inserted powder injection molding (IPIM) method has been developed [4]. In this method, the part called insert is placed into the mould and the feedstock is injected onto it. It is possible to produce functional parts consisting of different materials supposing that the bonding is obtained during sintering [4,5]. However, when parts are produced by using different materials such as metal insert and ceramic feedstock, physical and chemical characteristics of the materials significantly affect the desired strength value in the inter section [6,7]. In literature, a number of researches was made on bonding of WCCo and steel by different methods like diffusion welding and soldering [8–10]. In some studies about this subject, it is emphasized that diffusion is better and shear strength is increased in the intermediate region when an interlayer is used while bonding WC-Co and steel [11,12]. Barrena et al. (2010) [10] obtained 620 MPa shear strength by using
Ni/Cu interlayer in bonding of WC-Co and 90MnCrV8 steel, Jiang et al. (2016) [13] obtained 366 MPa shear strength by using Ag–Cu–Zn–Mn–Ni alloy in bonding WC-Co and 35CrMo steel, Guo et al. (2016) [14] obtained 293 MPa shear strength by using Ni interlayer in bonding WC-Co and 40 Cr steel, Feng et al. (2013) [15] obtained 195 MPa shear strength by using Ni interlayer in bonding WC-Co and 410ss steel and, Chen et al. (2012) [16] obtained 154 MPa shear strength by using Ni/Cu–Zn/Ni interlayer in bonding WC-Co steel. Simchi and Petzoldt, in their study [17], investigated the sintering behaviors of the parts produced by mounting with powder injection molding method from the WC-Co and 316L feedstocks. In their study, it is stated that the different stresses between the materials caused interfacial delamination, the liquid phase formed at 1220 °C due to diffusion of C and Co in the contact regions of the materials and the dimensional stability is affected from liquid phase formed. Besides, in the study, there is no data on shear strength regarding bonding. In the literature, part production by IPIM method is limited. In this study, parts whose inner side was AISI 4340 and outer side was WC-Co were prepared. Nickel interlayer was used for the full bonding of the inner and outer sides. The effect of nickel interlayer bonding process between inner and outer sides was investigated. As a result of
* Corresponding author. Technical Sciences Vocational School of Higher Education, Gazi University, Ankara, 06374, Turkey. Tel.:0 312 354 84 01, Fax.: 0 312 354 38 35 E-mail address: [email protected] (M. Subaşı).
https://doi.org/10.1016/j.ceramint.2019.07.261 Received 15 May 2019; Received in revised form 10 July 2019; Accepted 22 July 2019 Available online 23 July 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Ceramics International 45 (2019) 22331–22335
H. Koçak, et al.
Fig. 2, diffusion bond between outside and inside parts was achieved during the sintering process. It is thought that with the use of steel in the inner region and WC-Co in the outer region of the part will make the it qualified and optional in terms of both toughness and wear of the part.
Table 1 Technical characteristics of feedstock. Powder shape
Density (g/cm3)
Powder size (μm)
Complex shaped
8.06
D10 0.15
D50 0.28
D90 0.52
3.1. Bonding at WC- Co/Ni and Ni/4340 interfaces experiments at 1250 °C with three different sintering times (120-240360 min), the effect of nickel interlayer thickness (25, 50, 100 μm) on shear strength was investigated. 2. Materials and methods 2.1. Preparation of inserts and application of interlayer Inner side of the samples consisted of AISI 4340 steel insert whereas the outer side was WC-Co (9%) feedstock. The feedstock was supplied from Ryer firm availably. Technical attributes of WC- 9% Co feedstock are given in Table 1. Chemical compositions of insert materials and feedstock are given in Table 2. Before the injection process, the cylindrical inserts prepared from AISI 4340 steel material were coated with 25–50-100 μm Ni of ± 3 μm tolerance through electrolytic coating for the application of interlayer. Coating conditions are given in Table 3. After coating, the coating thickness was measured from the diameter surface using maXXi 5 X-Ray measuring device. 2.2. Inserted powder injection molding Injection process was made at the ARBURG Allrounder 220 S injection molding machine. Nickel coated inserts were placed into the mould and feedstock was injected onto them (Fig. 1). Optimum injection parameters were determined according to the producer's advice and type of product. Parameters used in the injection process are given in Table 4.
In order to understand how the bonding process took place at the WC-Co/Ni and Ni/4340 steel interfaces, the microstructure of the intermediate zone was examined. In the microstructure images, it was observed that WC-Co and AISI 4340 steel was successfully bonded and a gray color diffusion zone of 35 μm wide was determined at the Ni/4340 steel interface (Fig. 3a). In this study sintering temperature was 1250 °C and atomic diameters of nickel (0.125 nm) and iron (0.124 nm) elements were close to each other [18]. Therefore, the conditions are quite suitable for diffusion at the Ni/4340 steel interface. Zhong et al. (2009), in their study about bonding of tungsten and stainless steel with Ni interlayer, determined that nickel and iron could make solid solution owing to diffusion of Ni and Fe atoms correspondingly at high temperature [11]. In Fig. 3a, the same bonding process at Ni/4340 steel interface with diffusion is also seen in our study. When the WC-Co/Ni interface was examined, an infiltration of Ni interlayer (during sintering) was detected towards 10 μm inside of the WC-Co (Fig. 3b). Vaidya et al.(1998) [19], in their study, stated that the melting temperature of the Fe–Ni–Co–W–C phase was 1200–1300 °C depending on composition. It is thought that a Ni dominant Ni–Fe–Co–W–C liquid phase was created at the WC-Co/Ni interface with the diffusion of iron towards WC-Co side at 1250 °C sintering temperature. Ni dominant liquid phase was infiltrated into the WC powders by the effect of capillary pressure into the injected zone. Consequently the possible defects at the WC-Co/Ni interface decreased and bonding strength increased due to interlocking at the interface. 3.2. Effect of interlayer thickness and shear strength of intermediate zone
2.3. Debinding and sintering Samples were kept in ethanol at 60 °C for 48 h for debinding and after they were dried in a furnace at 60 °C. Following the debinding processing, the samples were sintered at 1250 °C under the control atmosphere (95 %N2 and 5% H2) for 120-240-360 min durations. In this study, heating rate is 5 °C/min in sintering process. 2.4. Mechanical tests and analyses Shear tests were carried out in accordance with TS EN ISO 6892-1 standard by using Instron testing device of 50 kN loading capacity at 1 mm/min constant speed. After sintering, micro hardness (HV0.2) measurements were made in 0.2 mm intervals and the hardness profile of the intermediate zone was obtained. The image examinations were made with the LEICA light microscope, and EDS analyses were made with JEOL JSM-6060LV Scanning Electron Microscope (SEM). 3. Results and discussion In this study, by using Ni interlayer, samples whose outer sides were WC-Co and the inner sides were AISI 4340 steel (Fig. 2) were produced by Inserted Powder Injection molding method. In the sample shown in
In the tests three Ni interlayers in different thicknesses (25-50100 μm) was used. Better results were obtained for shear strength and micro structure by using 100 μm interlayer. Micro structure of the intermediate zone became more regular as the thickness of interlayer increased. In Fig. 4a, it was observed that there was no defect in the intermediate zone and the interlayer thickness increased from 100 μm to approximately 160 μm after sintering. In Fig. 4b, it was seen that gaps were created in the middle of 50 μm interlayer and in Fig. 4c both greater gaps and cracks were found in the 25 μm interlayer. In bonding process of different materials such as metal and ceramic, thermal expansion difference between materials causes residual stresses while the sample is cooling. These residual stresses results in damages like cracking and separations in the intermediate zone. When an interlayer is used between metal and ceramic material, the plastic deformation formed in the interlayer decreases the residual stresses and a stronger bonding process is obtained. Vaidya et al.(1998) reported that when the intermediate layer thickness increases, the thermal expansion difference is better tolerated due to presence of high volume of intermediate layer material for plastic deformation, and both residual stresses and errors in the intermediate zone are reduced [19]. In the other studies in literature, it is also stated that residual stresses and defects in the intermediate zone decrease as the thickness of interlayer
Table 2 Chemical composition of the materials.
AISI 4340 WC-Co
C
Si
Mn
Cr
Mo
Ni
V
W
Co
P
S
Fe
0.39 5.54
0.22 –
0.67 –
0.78 0.01
0.24 0.01
1.74 0.01
– –
– bal.
– 8.94
0.025 –
0.025 –
bal. 0.01
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Table 3 Conditions of electrolytic coating. Anode
Bath temperature
Electrolytic Nickel
50–60 °C
Voltage
Current density
2.5–3 V
2
4A/dm
Waiting time 1 μm for 2 min
Fig. 1. Inserted powder ınjection molding (IPIM) process. Table 4 Powder injection molding parameters. Injection temperature
Injection pressure
Holding pressure
Injection rate
Mould temperature
200 °C
280 bar
80 bar
10 ccm/s
60 °C
Fig. 2. The part produced by the IPIM method (after sintering at 1250 °C).
increases [20,21]. In our study the same results were obtained too. Gaps in the inner side of interlayer and cracks near the interface were observed as the interlayer thickness decreased. Defects at the intermediate zone decreased as the interlayer thickness increased. In the tests, the highest value of shear strength was obtained as 266.5 MPa. Guo et al.(2016) [14] obtained 293 MPa shear strength in the bonding process of WC-Co 40Cr steel using Ni interlayer, Feng et al. (2013) [15] obtained 195 MPa in the bonding process of WC-Co and 410ss steel by using Ni interlayer again, Chen et al.(2012) [16] obtained 154 MPa in the bonding process of WC-Co 3Cr13 steel using Ni/ Cu–Zn/Ni interlayer. In this study, the bonding process was made during sintering without vacuum. In spite of the fact that no pressure was applied as in the diffusion welding process, shear strength value is higher than a number of studies in literature. The highest shear strength value was obtained by using 100 μm Ni interlayer. Increasing interlayer thickness increased the shear strength. Similar to literature, increasing interlayer thickness decreased the defects in the intermediate zone (Fig. 4) and consequently the shear strength increased (Fig. 5). It is observed that sintering time was also effective on the shear strength. When the graph is examined in Fig. 5, it is seen that shear strength increases as the sintering time increases. In Fig. 3, it is also seen that Ni interlayer diffuses towards the steel side and infiltrates towards the WC-Co side. Kurt et al. (2007), in their study stated that as the duration of process increased shear strength also increased with the increasing diffusion between the bonded materials [22]. Jadoon et al. (2004) [23] indicated that in bonding ceramic and metallic materials, a closer contact was provided at the interface with the infiltration of interlayer towards the ceramic side and then a mechanical locking
Fig. 3. Micro structure of interfaces (1250 °C, 240 min, 100 μm Ni).
occurred, therefore the shear strength increased. In this study, as the sintering time increased diffusion and infiltration also increased and consequently the shear strength value raised (Fig. 5). In the literature, generally, the temperature in the process of diffusion bonding of WC and steel ranges from 900 °C to 1100 °C and the time ranges from about 10 min to 60 min. In this study, since the experiments were performed at 1250 °C and for 120, 240, 360 min periods, diffusion and infiltration increased in the intermediate region of Ni interlayer. Thus, both the errors in the intermediate region decreased and the shear strength of the intermediate region was provided to be higher than the literature. 3.3. Element transitions in the 4340/Ni/WC-Co intermediate zone It is stated that in the spectral analysis report of 4340 material taken from the firm, the Fe and Ni percentages were 95.91% and 1.74% respectively and there was no W and Co (Table 2). Following sintering process, EDS analyses were made on 10 points in the intermediate zone and the graph in Fig. 6 was obtained from the results. After sintering, it was observed that in the area of 4340 insert where the EDS analysis was made, Fe amount dropped to 74.2% and the ratio of diffused W and Co from WC-Co towards the insert is 13.7% and 4.41%, respectively. But the Ni amount in the 4340 insert didn't change significantly. Ni amount diffused from Ni interlayer towards WC-Co side was 1.82% averagely.
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Fig. 4. Effect of interlayer thickness.
Fig. 7. Hardness profile of intermediate zone (1250 °C, 240 min, 100 μm Ni).
3.4. Hardness profile of intermediate zone Fig. 5. Effect of sintering time and interlayer thickness on shear strength (1250 °C).
Fig. 6. Element concentration profile at the intermediate zone (%), (1250 °C, 240 min).
In the different studies of literature made for bonding WC-Co and steel with diffusion welding process, temperature was in the interval of 850–1100 °C and remarkable results were obtained in terms of both diffusion and strength by using Ni [10,14,16]. Because WC-Co and 4340 steel are bonded during sintering, the temperature is higher than studies in the literature and this allows sufficient element diffusion for bonding. In the EDS analysis, W transition is more than the other elements. Besides, although the atomic diameter of nickel was smaller, cobalt diffused into the insert more than nickel. Both of them can be explained with the concentration difference. In the diffusion mechanism, when the difference of element amount between two materials increases, the rate of element transition between materials also increases due to high concentration gradient [24]. W was diffused more than other elements to 4340 insert due to high concentration gradient. Besides diffusion ratio of cobalt was much more than nickel due to 9% (by weight) Co on the WC-Co side.
Hardness profile of intermediate zone is given in Fig. 7. According to this profile, the hardness of the insert was measured as 374–400 HV near the intermediate zone. However the hardness of the insert center was measured as 305 HV. Hardness of the injected zone was determined between 450 and 1383 HV (Fig. 7). After 0.8 mm from the intermediate zone, the hardness of WC-Co was found to be around 1400 HV without much change. Hardness of AISI 4340 insert was higher at the points close to intermediate zone but hardness of WC-Co was lower. This is because of the element diffusion between AISI 4340 insert and WC-Co during sintering and must be evaluated with EDS analysis. AISI 4340 insert contains 1.74% Ni. From the EDS analysis, it is seen that a diffusion of 13.7% W, 4.41% Co to 4340 insert and 1.22% Fe, 1.7% Ni to WC-Co side. In some studies on diffusion welding method, it is stated that W, Ni and Co diffused to steel side, creating an intermetallic compound and solid solution in the diffusion zone and consequently hardness changes at the points close to intermediate zone [10,11]. As a result, whereas W and Co (diffused to insert) increased the hardness of insert at the points close to intermediate zone and Fe and Ni (diffused to WC-Co side) caused a decrease in the hardness of WC-Co.
4. Conclusions With Inserted Powder Injection Molding (IPIM) method AISI 4340 steel insert and WC-Co were successfully bonded during sintering process. It was found that there is a diffusion zone of approximately 35 μm at the Ni/4340 interface and an infiltration of the Ni interlayer into WCCo with a depth of 10 μm. It was found that after sintering, the interlayer, which was 100 μm, increased to approximately 160 μm. It was found that gaps formed in the middle part of the 50 μm interlayer. It was found that both larger gaps and cracks at 25 μm interlayer thickness. As the thickness of the interlayer increased, the microstructure of the intermediate zone became more regular. The highest shear strength value was obtained at 100 μm Ni thickness. The highest shear strength value (266.5 MPa) in AISI 4340 steel insert and WC-Co interface was obtained at 100 μm Ni thickness.
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As the sintering time and the thickness of the interlayer increase, the shear strength generally increases. The highest shear strength was obtained in samples sintered at 1250 °C and for 240 min. Since the difference in W concentration was higher than the other elements, there was 13.7% diffusion rate in the insert with WC-Co in samples sintered at 1250 °C and for 240 min. W and Co diffused to the insert increased the hardness of insert in the region near the intermediate zone. Fe and Ni diffused to the WC-Co side caused a decrease in the hardness of WC-Co. While hardness of the insert in the regions close to the intermediate zone of the sintered samples at 1250C for 240 min is between 374 and 400 HV, hardness average in the parts close to the center of insert is 305 HV. The hardness of the injected area is 1383 HV utmost. The results of research can be used in all applications where toughness of the inner part and abrasion resistance of the outer part are desired high. These results can be used, for example, in the production of cutting tools. Acknowledgement This research was sponsored by the Scientific and Technological Research Council of Turkey (TÜBITAK), Project No: 115M437 and Gazi University Research Funds, Project No: 07/2016-21. The authors would like to express their sincere appreciation to TÜBITAK organization and Gazi University for their financial supports. References [1] Z. Baojun, Q. Xuanhui, T. Ying, Powder injection molding of WC–8%Co tungsten cemented carbide, Int. J. Refract. Metals Hard Mater. 20 (2002) 389–394. [2] A. Safarian, M. Subaşı, Ç. Karataş, Reducing debinding time in thick components fabricated by powder injection molding, Int. J. Mater. Res. 106 (2015) 527–531. [3] Ç. Karataş, S. Sarıtaş, Toz enjeksiyonla kalıplama: bir ileri teknoloji imalat metodu (Turkish), Journal of the Faculty of Engineering and Architecture of Gazi University 13 (1998) 193–228. [4] A. Safarian, M. Subaşı, Ç. Karataş, The effect of sintering parameters on diffusion bonding of 316L stainless steel in inserted metal injection molding, Int. J. Adv. Manuf. Technol. 89 (2017) 2165–2173. [5] H. Koçak, K. Samet, O. Yılmaz, Ç. Karataş, Investigation of composite part production from WC-Co/HSS using nickel interlayer by inserted powder injection molding method, Gazi University Science Journal: PART:C Design and Technology 6 (2018) 374–384. [6] A. Passerone, M.L. Muolo, Metal-ceramic interfaces: wetting and joining processes, Int. J. Mater. Prod. Technol. 20 (2004) 420–439.
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