A comparative study on fiber laser and CO2 laser welding of Inconel 617

A comparative study on fiber laser and CO2 laser welding of Inconel 617

Accepted Manuscript A comparative study on fiber laser and CO2 laser welding of Inconel 617 Wenjie Ren, Fenggui Lu, Renjie Yang, Xia Liu, Zhuguo Li, S...

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Accepted Manuscript A comparative study on fiber laser and CO2 laser welding of Inconel 617 Wenjie Ren, Fenggui Lu, Renjie Yang, Xia Liu, Zhuguo Li, Seyed Reza Elmi Hosseini PII: DOI: Reference:

S0261-3069(15)00122-3 http://dx.doi.org/10.1016/j.matdes.2015.03.033 JMAD 7149

To appear in:

Materials and Design

Received Date: Revised Date: Accepted Date:

19 December 2014 2 March 2015 19 March 2015

Please cite this article as: Ren, W., Lu, F., Yang, R., Liu, X., Li, Z., Hosseini, S.R.E., A comparative study on fiber laser and CO2 laser welding of Inconel 617, Materials and Design (2015), doi: http://dx.doi.org/10.1016/j.matdes. 2015.03.033

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A comparative study on fiber laser and CO2 laser welding of Inconel 617 Wenjie Ren1, Fenggui Lu1, Renjie Yang2, Xia Liu2, Zhuguo Li1,*, Seyed Reza Elmi Hosseini1 1

Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials

Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China 2

Shanghai Electric Group Company Limited, 200240, China

*Corresponding author:Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. Tel.: (+86)02154745878. E-mail address: [email protected] Abstract: A comparative study on the influence of fiber laser welding (FLW) and CO2 laser welding (CLW) on the weld bead geometry and the microstructure of fusion zone (FZ) of Inconel 617 was investigated. In CLW joints, the weld bead geometry is Y-type shape. In FLW joints, the weld bead geometry transforms from Y-type to I-type with the decrease of the heat input. The minimum heat input required to achieve the full penetration of the weldment in FLW is lower than the CLW. The melting efficiency in FLW is higher than that in CLW. From the top to the root regions, the secondary dendrite arm spacing (SDAS) in fiber laser welded FZ undergoes a smaller change than that in CO2 laser welded FZ. The elements of Ti, Mo, Cr and Co segregate into the interdendritic regions both in FLW and CLW process. The second phases in CLW with the highest input of 360 J/mm are much larger and more than ones in FLW with the highest heat input of 210.5 J/mm. Key words: Inconel 617; Fiber laser welding; CO2 laser welding; Secondary dendrite arm spacing; Heat input 1. Introduction

1

Solid-solution strengthened Ni-base Inconel 617 (UNS N06617) superalloy consists of high amounts of solid solution elements (Mo, Cr and Co). The superalloy has an exceptional combination of excellent oxidation resistance, superior mechanical properties and high temperature phase stability above 980

。C,

so it has been widely used in the high temperature applications, e.g.

gas turbine boiler tubes, combustion chambers and Very High Temperature Reactor (VHTR) [1-2]. In recent years, transient liquid phase (TLP) bonding, cold metal transfer (CMT) welding and TIG welding have been used for welding of Inconel 617 [3-5]. Compared with the fusion welding and the TLP bonding, the laser has the higher power, higher cooling rate and higher beam quality which can produce deeper and narrower weldment even in the low heat input condition [6]. Laser beam welding has been recognized as one of the most attractive welding technologies and has been used to joint many superalloys. The dendritic micro-segregation, microstructure and the weld bead geometry considerably influence the properties of welded joint. Gobbi et al.

[7]

have

conducted a comparative study on the high power CO2 and Nd-YAG laser welding of wrought Inconel 718. The result showed that the high power CO2 laser was suitable for the post-welding of the joints which can create a high ratio of depth to width in the bead, whereas the Nd-YAG pulsed laser was suitable to form a uniform bead profile. The fusion zone (FZ) microstructure of the superalloys is significantly influenced by microsegregation and nonequilibrium phase transformations during the rapid solidification. Akin Odabasi et al. [8] have investigated that the low heat input in laser welded Inconel 718 leads to a fine dendritic structure. Osoba et al. [9] have reported that only Ti and Mo exhibit substantial partitioning into the interdendritic liquid and Ti-Mo rich MC-type carbides can be formed in the interdendritic regions of laser welded fusion zone of Haynes 282. Ming Pang et al.

2

[10]

have found that the laser

fusion zone region of K418 has nonequilibrium microstructure consisting of austenite dendrites containing Cr, Ni, Fe and C and some fine and dispersed Ni3(Al,Ti) phase as well as a few amounts of MC carbides enriched in Nb, Ti and Mo distributed in the interdendritic regions. The researches on the fiber laser welding (FLW) of the Inconel 617 are limited, especially on the comparative study with the CO2 laser welding (CLW). The aim of the present study is to conduct a comparative analysis on the weld bead geometry, microstructure, microsegregation and the hardness of the fusion zone of FLW and CLW processes . 2. Experimental procedure The chemical composition of Inconel 617 measured by inductively coupled plasma spectroscope (ICP) and carbon sulfur analyzer is summarized in Table 1. The plates (35 mm×15 mm×5 mm) were butt welded by using a fiber laser welding machine (IPG 10000) and a CO2 laser welding machine (TRUMPF). Laser system specifications are shown in Table 2. In this study, the laser welding parameters were selected based on the minimum heat input by choosing the high welding speeds which need to provide a full penetration in the joint. Laser welding parameters are listed in Table 3. The defocusing amount was 0 mm in both laser weldings. In order to prevent back weld oxidation, the back shielding gas (Ar) with flow rate of 4 L/min was used during the laser welding. The welded specimens were sectioned perpendicularly to the welding direction by using an electric discharge machine (EDM). The welded specimens were etched with a solution of 10 g FeCl3 + 100 ml HCl. The metallographic examination was investigated by using ZEISS model of optical microscope and the scanning electron microscope (SEM) of Quanta FEI 250 with energy dispersive X-ray spectrometer (EDS). Fig. 1 shows the various regions of FZ and the position of

3

samples for metallographic examination. The hardness measurement of the joints was carried out every 0.1 mm by the Zwick automatic hardness test machine from a point of 2.0 mm below the surface of the weld seam. Load of 2.94 N was used with a 15 s loading time. 3. Results and discussion 3.1 Microstructure of base material Fig. 2 shows a SEM micrograph of Inconel 617 in as-received condition which contains austenitic γ matrix with the equiaxed crystal. A large number of precipitates randomly distribute in grain boundaries and also inside the grains. According to the EDS measurement (Table 4) and previous studies on Inconel 617 [11-12], the particles are (Cr, Mo)-rich carbon boride M23(C, B)6 and M6C, and Ti-rich carbon nitride Ti(C, N), respectively, as shown in Fig. 2. 3.2 The weld bead geometry The effect of heat input on the weld bead geometry is given in Fig 3. In FLW, the full penetration can be achieved by using the highest heat input conditions of 210.5 J/mm (4000 W, 1140 mm/min), and it can also be obtained by using the lowest heat input conditions of 123.1 J/mm (8000 W, 3900 mm/min). The same result is also observed in CLW. The high power laser is used in the process and then creates the deep penetration. The undercut occurs both in the fiber and CO2 laser joints with the low heat input condition. The weld bead subsidence is observed in the fiber laser welded joints at heat input of 123.1 J/mm (8000 W, 3900 mm/min). It is also found that the minimum heat input required to achieve the full penetration of the weldment in FLW is lower than the CLW. In FLW, the lowest heat input of 123.1 J/mm and the highest heat input of 210.5 J/mm obtain the full penetration in the weldment. The lowest and highest heat input achieving the full penetration in the CLW is 257.1 J/mm and 360 J/mm,

4

respectively. Decreasing the heat input in the FLW process causes to change the weld geometry from “Y” shape to “I” shape, while this change is not observed in CLW. The surface region is much larger than the root region in the weld bead of “Y” shape, while the surface region is slightly larger than the root region in the weld bead of “I” shape. Fig. 4 shows the dimensions change of the joints as a function of the heat input. By increasing the heat input in FLW and CLW processes, a great increase in the width of the top region is obtained and the width of the root region is slightly decreased. In comparison with the fiber welded FZ, the significant dimension change in the width of the middle region is observed in CO2 welded FZ. The FZ area of CLW joint is much larger than that of FLW joint due to the higher heat input in CLW, however, the area of the FZ doesn’t vary monotonically with the increase of the heat input. In order to calculate energy loss in FLW and CLW, the melting efficiency η and power needed for the melting PF can be written as [13]: −



PF = ρ Sv[c s (Tm − T0 ) + ΔH F ]

(1)

η = PF / P

(2) −

Where P is the laser output power, ρ is the average density of Inconel 617 which equals to −

8.36×103 kg/m3 from room temperature to the melting point, C s is the specific heat of material equals to 541.36 J/(kg·。C) from room temperature to the melting point, HF is the latent heat of melting of material equals to 280000 J/kg, To is the room temperature, Tm is the melting point of material equals to 1380。C., S is the section area of fusion zone (Fig. 4), and ν is the laser scanning speed. The melting efficiency in FLW is higher than the CLW if the full penetration occurs in the joint, as shown in Fig. 5. The melting efficiency (η) in FLW is first raised and then dropped, but it is decreased monotonically in CLW. It is becasue that the changes of the melting efficiency are

5

concerned with the critical speed with vaporization of key hole in the laser welding [14]. The change of weld bead geometry and melting ratio in FLW and CLW processes mentioned above are related to the type of laser source. First, the laser wavelength of FLW (1.07 μm) is shorter than the laser wavelength of CLW (10.6 μm). The short wavelength of fiber laser cause that the laser is weakly absorbed by plasma in FLW. Second, the threshold power density required to produce laser-induced plasma is approximately two orders higher than that of CO2 laser with wavelength

[15]

. A small number of laser-induced plasma is produced in FLW. The small

plasma/vapour absorption does not interrupt the fiber laser welding process and enhances the beam energy density and penetrating power[16]. In addition, the efficiency of the energy transfer laser can be improved and the energy density of the laser acting on the superalloy is increased greatly in FLW. The intenser laser energy is absorbed by the base material in FLW. The recoil pressure of evaporation in FLW with the high laser power is intenser than that in CLW. The weld bead subsidence arises from the downward melt flowing along the front keyhole, which is caused by the intense recoil pressure of evaporation [17]. Thus, the weld bead subsidence occurs in FLW with the high laser power. 3.3 The microstructure of FZ Fig. 6 shows the microstructure of the different regions in the laser welded FZ. The figure shows that the columnar dendrites growth is directional in the all regions of the weld FZ due to the direction of heat flow. As well known, the smaller dendrite arm spacing results in the finer dendritic microstructure. In this study, the mean values for the secondary dendrite arm spacing (SDAS) in the center line of FZ are quantified by using Image-Pro Plus 6.0 to measure 100 secondary dendrite arms. Fig. 7 (a)

6

and (b) show that the SDAS of the top, middle and root regions increases with increasing heat input, and depends on the cooling rate in the mushy zone (the range from liquidus to solidus), which is calculated from the empirical equation [4]:

λ = K ⋅ Rn (3) where λ is the secondary dendrite arm spacing, K and n are material constants (n = -0.378 and K=319.4 μmK1/3s-1/3), and R is the cooling rate [4]. Fig. 7 (c) and (d) show that the cooling rate in the top, middle and root regions decreases when the heat input increases. In the top region, the cooling rate is in the range of 1.27×105 - 3.58×105 K/s in FLW and 0.86×105 - 1.52×105 K/s in CLW, which are agreement with that in the previous reports

[18, 19]

. Since the cooling rate in the laser welding is

high (104 - 105 K/s), and the microstructure of the weld tends to be dendritic structure. The larger dendrite arms grow at the expense of the smaller ones which have more surface area per unit volume and it is known as the secondary dendrite ripening

[20]

. High heat input can drive the

secondary dendrite arm to enlarge as a result of the slower cooling rate. The SDAS for the top region is larger than the middle and root regions in CLW joint, because the cooling rate of the top region is lower than the other regions. The cooling rates of the top, middle and root regions of the CLW joint at the constant heat input of 257.1 J/mm are 1.52×105 K/s, 2.24×105 K/s and 2.01×105 K/s, respectively. The top region of melting pool in CLW can absorb more heat from the plasma vapour than the FLW, so the SDAS in FLW joint undergoes a small variation from the top to the root region. The cooling rates of the top, middle and root regions of FLW joint are 1.27×105 K/s, 1.38×105 K/s, and 1.50×105 K/s under the constant heat input of 210.5 J/mm, respectively. The cooling rate in welded FZ can influence the microsegregation of elements. In order to

7

study the segregation of elements in the welded FZ, the chemical composition of 10 points in the dendrites core near the fusion line where the solidification begins during the welding process are measured by SEM/EDS. Table 5 shows the chemical composition of the dendrite core region in FZ of the CLW and FLW under different heat inputs. The concentration of Al, Ti, Mo, Cr and Co in the dendrites core region is lower than the base material, especially the concentration of Ti is dramatically lower. The concentration of Ni and Fe in the dendrites core is higher than the base material. There is no visible change in the chemical composition of the dendrite core with increasing the heat input on account of small ratio of cooling rate and semiquantitative SEM/EDS analysis. According to Fig. 7, the rapid cooling rate reduces the diffusion rate of the solute atoms in the solid. Neglecting the undercooling during the solidification process and assuming complete mixing in the liquid and no diffusion in the solid, the solute redistribution can be described by the following equation [21]: CS = kC0 [1 − f s ]( k −1)

(2)

where Cs is the composition of solid in the solid/liquid interface, C0 is the nominal composition of initial liquid and fs is volume fractions of the solid. When fs = 0, the Cs is equals to kC0. Therefore, the distributed coefficient (k) is the ratio of the dendrite core composition (Cs) to that in the base metal (C0) at the beginning of solidification process, are given by k = Cs/C0. As an alloy element k<1, the elements can segregate into the interdendritic region. A k-value near unity indicates that the dendrite core composition will be close to the nominal composition and the elements will show a little tendency to segregate into the interdendritic liquid. Table 5 also lists the distributed coefficient (k) under the different heat inputs. The k values of Ti are 0.71, 0.76, 0.79 and 0.68 in different heat

8

inputs, respectively. These values are considerably less than 1, indicating that Ti microsegregates strongly into the inter-dendritic regions. The k values of Mo, Cr and Co are lower than 1, which imply that Mo, Cr and Co also microsegregate into the interdendritic regions but to a much smaller degree compared with Ti. Ni and Fe have k values greater than unity, indicating that these elements segregate into the dendrite core region. The distributed coefficient of the elements is not affected significantly by heat input in laser welding. The SEM photograph and EDS spectra analysis of phases taken from the top region in fiber laser and CO2 laser welded FZ under different heat inputs are presented in Fig. 8. The irregular-shaped secondary particles marked by arrows are located in the interdendritic regions both in fiber laser and CO2 laser welded FZ, as shown in Fig. 8 (a-b) and 9 (a-b). The EDS spectra displays that these phases are enriched with Mo and Cr, as implied in Fig. 8 (c-d) and 9 (c-d). Similarly, the Mo concentration in these phases increases with increasing heat input, i.e. from 18.65 to 27.73 wt. % in FLW and from 29.96 to 34.64 wt. % in CLW, as shown in Table 6. The microsegregation of the elements such as Mo, Cr, and Ti into the interdendritic regions leads to the formation of a second phase at the end of solidification. The second phase particles such as interdendritic eutectics of γ/M23C6, which are rich in Cr and Mo, can be formed in the interdendritic regions of Inconel 617 alloyed layer by TIG welding[22]. Lippold et al.[23] showed that interdendritic (Cr, Mo)-rich eutectic constituent in the FZ of Inconel 617 was predicted by the Scheil-Gulliver simulations and measured with SEM/EDS. Similarly, the second phase in the laser welded FZ can also be (Cr, Mo)-rich carbide. The cooling rate can influence the formation of the second particles. The volume fraction and the size of the second particles of 15 SEM images (×5000) of FZ under different heat input are

9

measured by using Image-Pro Plus 6.0, as presented in Fig. 10. The average surface area of the particles in the fiber laser welded FZ with the heat input of 123.1 J/mm is about 0.06 μm2, which is lower than that of those particles with 0.23 μm2 in the weld with the heat input of 210.5 J/mm. In CO2 laser welded FZ, the size of the second phase particles increases from 0.16 μm2 to 0.4 μm2 with increasing heat input from 257.1 J/mm to 360 J/mm. The average volume fraction of the secondary particles decreases from 4.64 to 2.46 vol. % in CO2 laser welded FZ and from 2.44 to 0.49 vol. % in fiber laser welded FZ with decreasing in heat input. The higher heat input (e.g. 360 J/mm) results in the slower cooling rate, which can increase the diffusion of elements and provide more time for precipitation and growth of phases, so a lot of large (Mo, Cr)-rich phases form in the laser welded FZ. Increasing the cooling rate decreases the SDAS, and subsequently the terminal liquid is divided into many small particles. In addition, the diffusion of solute atoms and the time required for the growth of the second phase particles is reduced when the heat input decreases. Therefore, a small quantity of the finer particles form in the lower heat input. During the solidification of the weld, the reduction in the heat input not only refines the particles significantly but also decreases the volume fraction and Mo concentration of the second phases both in FLW and CLW joints. 3.4 Hardness The hardness values of the fiber laser welded FZ and CO2 welded FZ under different heat inputs are depicted in Fig. 11. The hardness of FZ increases from 234.7 HV to 259.4 HV as the heat input decreases from 210.5 J/mm to 123.1 J/mm in fiber laser welded joints. The hardness rises from 225.7 HV to 240.1 HV as the heat input is reduced from 360 J/mm to 257.1 J/mm in CLW joints. With increasing hardness, the SDAS of the middle region decreases from 3.64 to 2.44 μm and from 3.46 to 3.03 μm respectively in fiber laser welded FZ and CO2 laser welded FZ, as shown

10

in Fig. 11. On the other hand, the SDAS decreases with increasing the heat input in both FLW and FLW joints. The smaller SDAS leads to the finer dendrites. In summary, the average hardness of FZ increases as the heat input is decreased due to the smaller SDAS. 4. Conclusions 1. The minimum heat input required to achieve the full penetration of the weldment in FLW was lower than the CLW. As heat input decreased in the FLW, the weld shapes changed from the “Y” shape to the “I” shape, while no change of the weld shape was observed in CO2 laser welded joint. The melting efficiency of FLW was higher than that of CLW. 2. With increasing the heat input, the SDAS in the top, middle and the root regions increased and the cooling rates decreased in two laser welded FZ. The SDAS of the top region was much larger than of the middle and root regions in CO2 laser welded FZ compared with that of fiber laser welded FZ. 3. The elements Ti, Mo, Cr and Co segregated into the interdendritic regions, while Ni and Fe partitioned into the dendrites core regions in the FZ of both two processes. The area, volume fraction and Mo concentration of the second phases in CLW with the highest input of 360 J/mm are much larger than ones of FLW with the highest heat input of 210.5 J/mm. 4. The hardness of both laser welded FZ increased as heat input decreased as a result of the smaller secondary dendritic dendritic spacing. Acknowledgments The authors appreciate the financial support from the science and technology research program of Shanghai science and technology committee (Project No. 13DZ1101502). References

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[1] Wang J, Dong JX, Zhang MC, et al. Equilibrium-phase precipitation behaviors of typical nickel-base alloys for 700。C. J Univ Sci Technol B. 2012, 34, 7: 799-807. [2] Mankins WL, Hosier JC, Bassford TH. Microstructure and phase of INCONEL alloy 617 Stability. Mater. Trans. 1974, 5: 2579-2590. [3] Carolin Fink·Manuela Zinke. Welding of nickel-based alloy 617 using modified dip arc processes. Weld World. 2013, 57: 323-333. [4] Jalilian F, Jahazi M, Drew RAL. Microstructural evolution during transient liquid phase bonding of Inconel 617 using Ni-Si-B filler metal. Mater Sci Eng A. 2006, 423: 269-281. [5] Young SP, Hyo SH, Sang MC, et al. An assessment of the mechanical characteristics and optimum welding condition of Ni-based super alloy. Proc Eng. 2011, 10: 2645-2650. [6] Paleocrassas AG, Tu JF. Inherent instability investigation for low speed laser welding of aluminum using a single-mode fiber laser. J Mater Process Tech. 2010, 210: 1411-1418. [7] Gobbi S, Zhang L, Norris J, et al. High power CO2 and Nd-YAG Laser welding of wrought Inconel 718. J Mater Process Tech. 1996, 56: 333-345. [8] Akin O, NeciP U, GuLtekin G, et al. A Study on Laser Beam Welding (LBW) Technique: Effect of Heat input on the Microstructural Evolution of Superalloy Inconel 718. Metall Mater Trans A. 2010. 41A: 2357-2365. [9] Osoba LO, Ding RG, Ojo OA. Microstructural analysis of laser weld fusion zone in Haynes 282 superalloy. Mater Charact. 2012, 65: 93-99. [10] Pang M, Gang Yu, Wang HH, et al. Microstructure study of laser welding cast nickel-based superalloy K418. J Mater Process Tech. 2008, 207: 271-275. [11] Tytko D, Choi PP , Klower J, et al. Microstructural evolution of a Ni-based superalloy (617B)

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at 700。C studied by electron microscopy and atom probe tomography. Acta Mater. 2012, 60: 1731-1740. [12] Shah Hosseini H, Shamanian M, Kermanpur A. Characterization of microstructures and mechanical properties of Inconel 617/310 stainless steel dissimilar welds. Mater Charact. 2011, 62: 425-431. [13] Zhao YB, Lei ZL, Chen YB. Analysis of melting characteristics of laser-arc double-sided welding for stainless steel. Chinese J Lasers. 2013, 82, 0203001. [14] Lin ZJ, Kai WS , Shi XR, et al. Comparison of Melting Efficiency in High Power Fiber Laser and CO2 Laser Welding. Chinese J Lasers. 2013, 40 (8):1-5. [15] Wang J, Wang CM, Meng XX, et al. Study on the periodic oscillation of plasma/vapour induced during high power fibre laser penetration welding. Opt Laser Technol. 2012, 44: 67-70. [16] Mei LF, Yan DB, Yi JM, et al. Comparative analysis on overlap welding properties of fiber laser and CO2 laser for body-in-white sheets. Mater Des. 2013, 49: 905-912. [17] Zhang MJ, Chen GY, Zhou Y, et al. Observation of spatter formation mechanisms in high-power fiber laser welding of thick plate. App Surf Sci. 2013, 280: 868-875. [18] Zhang L, Lu JZ, Luo KY, et al. Residual stress, Micro-hardness and tensile properties of ANSI 304 stainless steel thick sheet by fiber laser welding. Mater Sci Eng A. 2013. 561: 136-144. [19] Torkamany MJ, Sabbaghzadeh J, Hamedi MJ. Effect of laser welding mode on the microstructure and mechanical performance of dissimilar laser spot welds between low carbon and austenitic stainless steels. Mater Des. 2012, 34: 666-672. [20] Voorhees PW. The Theory of Ostwald Ripening. J Stat Phys. 1985, 38: 231-252. [21] Osoba LO, Ding RG, Ojo OA. Microstructural analysis of laser weld fusion zone in Haynes

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282 superalloy. Mater Charact. 2012, 65: 93-99. [22] Arabi Jeshvaghani R, Jaberzadeh M, Zohdi H. Microstructural study and wear behavior of ductile iron surface alloyed by Inconel 617. Mater Des. 2014, 54: 491-497. [23] John L, Thomas BÖ, Carl E, Cross, editors. Hot Cracking Phenomena in Welds II. Berlin: springer. 2008, PP: 147-170.

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List of Figures Fig. 1. The schematic of various regions in the weldment Fig. 2. SEM micrograph of the base material Fig. 3. The change of the laser weld geometry in (a) FLW and (b) CLW techniques Fig. 4. The effect of the heat input on the weldment dimensions of (a) FLW and (b) CLW Fig. 5. The effect of heat input on the melting efficiency in FLW and CLW Fig. 6. The microstructure of fusion zone in different regions of the cross sections Fig. 7. The secondary dendrite arm and the cooling rate as a function of heat input in (a) & (c) FLW, (b) & (d) CLW Fig. 8. SEM photomicrograph and EDS spectrum of the particles marked via arrows in the FZ of FLW in different heat input (a) & (c) 123.1 J/mm, and (b) & (d)210.5 J/mm Fig. 9. SEM photomicrograph and EDS spectrum of the particles marked via arrows in the FZ of CLW in different heat input (a) & (c) 257.1 J/mm, and (b) & (d) 360 J/mm Fig. 10. Average surface area and volume fraction of the secondary particles under different heat inputs Fig. 11. SDAS and hardness as a function of the heat input (a) FLW and (b) CLW

15

Fig. 1. The schematic of various regions in the FZ

16

Fig. 2. SEM micrograph of the base material

17

Fig g. 3.. Thhe chaangee off the laaserr weld d geom metryy inn (aa) FLW W annd (b) CL LW tecchniiquues

188

Figg. 4. Thhe effeect of the heat inpuut on tthe FZ dim mennsio onss of (a)) FL LW and (bb) CLW W

199

Fig. 5. The efffectt off heat inpuut on the t meeltinng efficcienncyy inn FL LW andd CLW W

200

Fig g. 6. The miccrostru uctuure of fussion n zoone in diff ffereent reggionns of o thhe cro c ss ssecttionns ( top (a) t , (b b) midd m dle andd (cc) roott in FZ Z off FL LW (1223.11 J//mm m); ((d) topp, (ee) mid m ddlee annd (ff) root r t in FZ Z off CL LW W (2557.1 J//mm m)

211

Fig. 7. Thee seecondaary denndrrite arm m an nd thee cooolinng rate r e ass a fun f nctioon of heaat innputt inn ((a) & ((c) FLW LW, (b)) & (d)) CL LW W

222

Fig. 8.. SE EM phhotoomicro ograaph and EDS E S sppecttrum m of o thhe part p ticles m marrkeed via v aarroowss inn thee FZ Z of FL LW W inn diffferrentt heeat inp i put (a) ( & (c) ( 1233.1 J/m mm m, annd (b) ( & ((d) 2100.5 J/m mm m

233

Fig. 9.. SE EM phhotoomicro ograaph and EDS E S sppecttrum m of o thhe part p ticles m marrkeed via v aarroowss inn thee FZ Z of o CLW C W in i ddiffeeren nt heat h t innputt (a)) & (c)) 2557.1 J//mm m, and a d (b) & (dd) 3660 J/m J mm

244

Figg. 10. Aveeragge surffacee arrea and d voolum me fraactioon of the t secconndarry partticlees unndeer diffe d erennt heat h t inpputts.

255

Figg. 11. SDAS S annd harddness as a fu uncttionn off thee heeat inpput (a) FL LW andd (bb) CLW W

266

Table 1 The chemical composition (wt.%) of the as-received Inconel 617 Element

Ni

Cr

Co

Mo

Al

C

Fe

Mg

Si

Ti

Cu

B

AMS

Bal

20.0

10.0

8.0

0.8

0.05

3

1.0

1.0

0.6

0.5

0.006

-24.0

-15.0

-10.0

-1.5

-0.15

max

max

max

max

max

max

Bal

22.82

13.04

9.53

1.21

0.10

0.98

0.0035

0.12

0.38

0.089

0.0052

5888C measured

Table 2 Laser systems specifications Laser system

Maximum output power (kW)

Emission wavelength (nm)

Focal length (mm)

Focal point diameter (mm)

CLW FLW

15 10

10600 1070

350 300

0.86 0.72

Table 3 The parameters of the laser welding processes Welding method

Power (W)

Speed (mm/min)

Ar-Shielding gas (L/min)

4000

1140

10

5000

1500

10

Welding method

FLW

Power (W)

Speed (mm/min)

He-Shielding gas (L/min)

6000

1000

40

8000

1400

40

CLW 6000

2520

10

10000

2000

40

8000

3900

10

12000

2800

40

27

Table 4 The EDS results taken from the phases in Inconel 617 (wt. %) Phase

Ti

Cr

Co

Mo

Ni

Fe

M23C6

0.10

60.19

4.12

23.21

11.93

0.45

M6C

0.34

34.35

5.65

45.23

13.90

0.54

Ti(C,N)

60.41

14.89

3.53

11.91

9.27

-

Table 5 The chemical composition of the dendritic core and the distributed coefficient (k) as determined by EDS analysis Welding

Heat input

method

(J/mm) 257.1

CLW

Elements (wt. %)

Dendrite core

Al

Ti

Cr

Mo

Co

Fe

Ni

1.16

0.29

21.92

9.36

12.88

1.15

53.45

k

0.96

0.76

0.96

0.98

0.99

1.17

1.03

Dendrite core

1.20

0.27

21.90

9.27

12.94

1.10

53.26

k

0.99

0.71

0.96

0.97

0.99

1.12

1.02

123.1

Dendrite core

1.18

0.26

21.94

9.46

12.87

1.2

53.11

k

0.97

0.68

0.96

0.98

0.99

1.22

1.02

210.5

Dendrite core

1.17

0.28

21.84

9.18

12.94

1.12

53.47

k

0.97

0.75

0.96

0.96

0.99

1.14

1.03

360.0

FLW

Table 6 The chemical composition of the particles in the weld FZ in the different heat input conditions Welding method

Heat input (J/mm)

Al

Ti

Cr

Mo

Co

Fe

Ni

123.1

1.15

0.70

24.23

18.65

10.89

1.02

43.36

210.5

0.81

1.07

26.19

27.73

9.04

0.82

34.31

257.1

0.75

0.87

27.13

29.96

8.58

0.76

31.93

360.0

0.63

1.10

26.62

34.64

7.41

0.54

26.54

FLW

CLW

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Graphical abstract

Highlights

1. The difference change of weld bead geometry occurs in fiber and CO2 laser welding. 2. The melting efficiency in fiber laser and CO2 laser welding is analyzed. 3. Secondary dendrite arm spacing and cooling rate in two laser weldings is studied. 4. The second phase in two laser welding with different heat input is investigated.

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