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Effect of Scan Direction on Tensile properties and Fractography of Laser Additive Manufactured Maraging Steel
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 18 (2019) 3842–3848
www.materialstoday.com/proceedings
ICMPC-2019
Effect of Scan Direction on Tensile properties and Fractography of Laser Additive Manufactured Maraging Steel Tarun Bhardwaj, Mukul Shukla* Department of Mechanical Engineering, Motilal Nehru National Institute of Technology Allahabad, Prayagraj 211004, India
Abstract Laser additive manufacturing (LAM) is the process used to fabricate near net shape from metallic powders. A major challenge with LAM fabricated parts is the materials performance to achieve required mechanical properties. This work presents the fabrication of 18% Ni Maraging steel 300 (MS) using a LAM process by adopting two scan direction (bi-directional). The scan directions are selected in two perpendicular directions, one is parallel to the loading axis of the tensile specimen (0°) and another is in perpendicular direction to the loading axis of the tensile specimen (90°). Tensile properties and its fractography are investigated to analyse the scan direction effect due to the variation in thermal history. Further, to analyse the defect and pores in the fractured surface, scanning electron microscopy is used. The tensile properties of 90° scan direction are found to be higher owing to the nucleation and micro-void coalescence. This work facilitates to provide a better understanding of the selection of scan direction patterns for fabrication of better quality MS parts using the DMLS AM process. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Laser additive manufacturing; Maraging steel; Scan direction; Tensile properties; Fractography
1. Introduction Laser additive manufacturing (LAM) is a layer wise process used to fabricate the metal components by selectively fusing the powder using laser thermal energy [1,2]. Each layer is formed by overlapping of tracks results into a deposit. Direct metal laser sintering (DMLS), a LAM technique has widely been used for aerospace applications due to the obtained surface quality with minimal time in comparison of other AM techniques.
* Corresponding author. Tel.: +91 94519 92782; fax: +91 532 254 5341. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
3843
18% Ni-300 Maraging steel (MS) is a Fe-Ni alloy with low carbon content offers an ultra-high strength. The ultra-high strength of MS is established by heat treatment (aging at 480 °C for 6 h) due to the intermetallic precipitates formed during aging [3,4]. Owing to the high σ/w ratio (strength to weight), its application is well suited for safety-critical parts. MS applications in aerospace includes the motor casings, landing gears, rocket and missile skins, slat tracks and engine components [5,6]. Few illustrations of MS parts are displayed in Fig. 1 (a-b). (a)
(b)
Fig.1. Maraging steel parts (a) Rocket motor casing and (b) Landing and take-off gears Extensive literature is published to control and optimize the LAM process parameters for attaining fully dense parts [5,7]. Bai et al., 2017 [7] reported the influence of selective laser melting (SLM) process parameters on the relative density of MS 300 to attain fully dense parts. They also reported the influence of solution and aging treatment on the mechanical behaviour of MS 300. The found the decrease in tensile properties with increase in elongation while increase (nearly 200 %) by aging treatment. Casalino et al., 2015 [5] explored the energy density role on the porosity and mechanical properties. The optimum energy density of 2.78 J/mm2 is found to be desired for fully dense parts (> 99%) and high mechanical properties. Several literature is published on the influence of laser scan path/direction on the tensile properties of LAM parts due to change in solidification time and generated porosity in the physical parts. Liu et al., 2011 [8] analysed the outcomes of laser scan path (single direction and cross-direction) on the microstructure and tensile properties of LAM Inconel 718. They reported the inhibition of columnar dendrites and formation of fine grain size in crossdirection scan pattern in comparison of single direction results in increase of mechanical properties. Moreover, transgranular mode of fracture in cross-direction leads to high ductile behaviour. Dai et al., 2017 [4] investigated the influence of scan pattern and melt pool configuration on microstructure and mechanical properties of SLM AlSi12 parts. They reported the remelting as an efficient method to eliminate the pores. Rashid et al., 2017 [9] explored the influence of scan strategy (single scan and double scan of each layer) on SLM 17-4PH stainless steel density and metallurgical properties. They reported the increase in hardness (~32 %) by double scan due to uniform distribution of martensite dominant phase. Carter et al., 2014 [10] observed the effect of the laser scan pattern on grain structure and cracking behaviour of SLM CM247LC Ni super alloy. They also reported HIP effect on the island scan pattern. The bi-modal grain structure was found with two distinct regions. Fine grains were found on the top surface and elongated columnar grains in the build direction. Recently, Bhardwaj et al., 2018 [2] reported the effect of bi-direction and cross-direction strategy on the DMLS MS. They reported the high tensile properties are achieved in cross-directional scan than bi-direction scan due to suppression of columnar grains formed.
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T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
From the previous studies it is manifested that the scan direction significantly affects the tensile behaviour of LAM parts due to the difference in produced melt-pool configuration and porosity. In this study, tensile properties and fractography is analysed to investigate the effect of adopted scan directions. This research facilitates the fabrication of high strength and ductile MS parts using DMLS. 2. Materials and method In this work, MS powder (near spherical shape) of particle size 15-45 μm is provided by EOS GmbH (Germany) as shown in Fig. 2. The powder morphology facilitates the proper fusion of MS powder leads to reduced porosity.
Fig. 2. EOS MS powder morphology. The chemical constituent of MS is listed in Table 1. The large amount of Ni (17-19 %) results in the formation of soft martensite structures during aging. The constituents of Mo, Ti and Al is added to enhance the intermetallic precipitates formation during aging. However, they result in reduction of martensitic temperature (200-300 °C). To suppress their effect on martensitic temperature, Co is added in the matrix. MS has an advantage over other steels owing to low amount of carbon that avoids the formation of TiC precipitates leads to decrease in impact strength, ductility and toughness.
Table 1. Chemical composition of EOS MS. Element
Ni
Co
Mo
Ti
Al
Cr, Cu
C
Mn, Si
P,S
Fe
Weight (%)
~18
~9
~4.8
~0.7
~0.10
≤0.5
≤0.03
≤0.1
≤0.01
Bal.
T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
3845
In this work, samples are fabricated on the mild steel substrate using the EOSINT M280 DMLS LAM system. The system is available at Central Tool Room and Training Centre (CTTC), Bhubaneswar, India equipped with Ytterbium fibre laser (wavelength of 1060 nm). It includes maximum laser power of 400 W, scan speed upto 7000 mm/s and laser beam diameter of 100-500 μm. The oxygen level is maintained at 1.6%. Prior to sample fabrication, the base plate is pre-heated at 40 °C. The selected process parameters for samples fabrication as listed in Table 2 are based on our previous study [2]. The selection of process parameters was based on the optimization for reduced porosity and producing crack-free parts. Table 2. Selected process parameters for sample fabrication. Parameter
Value
Laser power
285W
Scan speed
960 mm/s
Hatch spacing
0.11 mm
Powder layer thickness
0.04 mm
(b)
(a)
(c)
(d)
(e) 8
90° 12 0°
40
2
Fig. 3. (a) 0° and (b) 90° laser scan direction adopted, (c), (d) samples of 0° and 90° respectively and (e) schematic representation of tensile specimen in this study.
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T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
In this research, two different scan directions 0° and 90° are selected as presented in Fig. 3 (a) and (b) respectively. Corresponding fabricated samples surface are displayed in Fig. 3 (c) and (d). The schematic representation of Sub-size tensile sample according to ASTM E8-16a is presented in Fig. 3 (e). The first adopted strategy (0°) is bi-directional to the axis parallel to the loading axis of the tensile specimen (0°) and another is in perpendicular direction to the loading axis of the tensile specimen (90°). Tensile tests are conducted using a BiSS UTM of maximum 25 kN load capacity. Tensile properties (3 samples of each scan pattern) are investigated at a cross-head speed of 0.5 mm/min. Fractography of fractured tensile specimens are investigated using scanning electron microscopy (Carl Zeiss EVO 50 SEM). 3. Results and discussion 3.1 Tensile test The tensile tests for both scan directions are generated using uni-axial tensile test at room temperature as shown in below in Fig. 4. Near similar elastic behaviour is exhibited for both scan directions. The tensile properties (YS, UTS and El) are obtained as summarized in Table 3. The obtained results of 90° tensile properties are in range of wrought MS [13]. The higher tensile properties are observed in 90° scan direction results in a high ductile failure. However, scan line 0° direction exhibits lower UTS and ductility due to the variation in scan direction leads to change in melt pool configuration and generated porosity after fabrication [11].
Fig. 4. Engineering stress-strain curve for 0° and 90° scan directions.
T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
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Table 3. Summary of tensile properties obtained for both scan directions. Scan direction
Yield Strength
Ultimate Tensile Strength
Elongation
(MPa)
(MPa)
0°
720±15
983.5±47.3
13.5±1.6
90°
780±25
1021.6±28.0
19±0.7
Wrought
760-895
1000-1170
6-17
(%)
3.2 Fractography The fracture surface morphology for both scan direction is obtained as presented in Fig. 5. The 90° scan direction exhibited high elongation owing to the nucleation and micro-void coalescence. While 0° scanning, large size deep holes of size ~100-110 μm (2-3 times than 90° scanning i.e. ~35-45 μm) is observed. The presence of large size holes results in early crack formation and lower tensile properties. Both scan direction shows quasi cleavage ductile failure. DMLS MS using 90° scan direction has higher ductility i.e. 40.74 % than 0° and ~10 % than wrought specimen [12]. Fractography of 90° samples as shown in Fig. 5 (b) depicts small sized holes along melt pool boundaries results in high ductile failure. Both the scan directions show quasi cleavage ductile failure as shown in Fig. 4 (a) and (b). Due to the variation in scan direction, the morphology of pores generated during fabrication will differ the crack initiation mechanism during applied tensile force. The variation in tensile behaviour is due to the generated pores along melt pool boundaries. (b) (a) Large deep holes Small size holes
Fig. 5. Fractography of fractured tensile surface for scan direction (a) 0° and (b) 90°. 4. Conclusions This study explored the effect of two scan direction (bi-directional) on the tensile properties for DMLS fabricated MS. The scan pattern / direction is investigated to have a strong influence on the tensile properties of the fabricated parts. The tensile properties of DMLS 90° scan direction are found in the range of wrought MS and they are recommended for fabricating higher elongation MS parts. Further, residual pores and stresses in the physical parts,
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post processing such as shot peening can be performed. The pore size of fabricated parts can be further reduced by aging treatment and hot isostatic pressing. Acknowledgements Thanks are largely due to Mr. A.B. Nayak of Central Tool Room and Training Center, Bhubaneswar, India for extending the DMLS facilities. One of the author Tarun Bhardwaj would like to thank the Ministry of Human Resource Development (MHRD), Government of India for financial assistance. References [1] I. Gibson, D.W. Rosen, B. Stucker, Additive Manufacturing Technologies: rapid Prototyping to Direct Digital Manufacturing, Springer, 2009, pp. 1-14. [2] T. Bhardwaj, M. Shukla, Effect of laser scanning strategies on texture, physical and mechanical properties of laser sintered maraging steel, Mat. Sci. Eng. A 734 (2018) 102-109. [3] A.G. Demir, B. Previtali, Investigation of remelting and preheating in SLM of 18Ni300 maraging steel as corrective and preventive measures for porosity reduction, Int. J. Adv. Manuf. Technol. 93 (2017) 2697-2709. [4] D. Dai, D. Gu, H. Zhang, J. Xiong, C. Ma, C. Hong, and R. Poprawe, Influence of scan strategy and molten pool configuration on microstructures and tensile properties of selective laser melting additive manufactured aluminum based parts, Opt. Laser Technol., 99, 91-100 (2018). [5] G. Casalino, S.L. Campanelli, N. Contuzzi, A.D. Ludovico, Experimental investigation and statistical optimization of the selective laser melting process of a maraging steel, Opt. Laser Technol. 65 (2015) 151-158. [6] T.H. Becker, D. Dimitrov, The achievable mechanical properties of SLM produced maraging Steel 300 components, Rapid Prototyping J 22 (2016) 487-494. [7] Y. Bai, Y. Yang, D. Wang, M. Zhang, Influence mechanism of parameters process and mechanical properties evolution mechanism of maraging steel 300 by selective laser melting, Mat. Sci. Eng. A 703 (2017) 116-123. [8] F. Liu, X. Lin, C. Huang, M. Song, G. Yang, J. Chen, W. Huang, The effect of laser scanning path on microstructures and mechanical properties of laser solid formed nickel-base superalloy Inconel 718, J. Alloys Comp. 509 (2011) 4505–4509. [9] R. Rashid, S.H. Masood, D. Ruan, S. Palanisamy, R.A. Rahman Rashid, M. Brandt, Effect of scan strategy on density and metallurgical properties of 17-4PH parts printed by Selective Laser Melting (SLM), J. Mater. Process Tech. 249 (2017) 502-511. [10] L.N. Carter, C. Martin, P.J. Withers, M.M. Attallah, The influence of the laser scan strategy on grain structure and cracking behaviour in SLM powder-bed fabricated nickel superalloy, J. Alloys Comp. 615 (2014) 338–347. [11] A. Kudzal, B. McWilliams, C. Hofmeister, F. Kellogg, J. Yu, J.T. Scarff, J. Liang, Effect of scan pattern on the microstructure and mechanical properties of Powder bed Fusion additive manufactured 17-4 stainless steel, Mater. Design 133 (2017) 205-215. [12] M.N. Rao, Progress in understanding the metallurgy of 18 % nickel maraging steels, Int. J. Mater. Res., 97 (2006) 1594-1607.
ScienceDirect Materials Today: Proceedings 18 (2019) 3842–3848
www.materialstoday.com/proceedings
ICMPC-2019
Effect of Scan Direction on Tensile properties and Fractography of Laser Additive Manufactured Maraging Steel Tarun Bhardwaj, Mukul Shukla* Department of Mechanical Engineering, Motilal Nehru National Institute of Technology Allahabad, Prayagraj 211004, India
Abstract Laser additive manufacturing (LAM) is the process used to fabricate near net shape from metallic powders. A major challenge with LAM fabricated parts is the materials performance to achieve required mechanical properties. This work presents the fabrication of 18% Ni Maraging steel 300 (MS) using a LAM process by adopting two scan direction (bi-directional). The scan directions are selected in two perpendicular directions, one is parallel to the loading axis of the tensile specimen (0°) and another is in perpendicular direction to the loading axis of the tensile specimen (90°). Tensile properties and its fractography are investigated to analyse the scan direction effect due to the variation in thermal history. Further, to analyse the defect and pores in the fractured surface, scanning electron microscopy is used. The tensile properties of 90° scan direction are found to be higher owing to the nucleation and micro-void coalescence. This work facilitates to provide a better understanding of the selection of scan direction patterns for fabrication of better quality MS parts using the DMLS AM process. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019 Keywords: Laser additive manufacturing; Maraging steel; Scan direction; Tensile properties; Fractography
1. Introduction Laser additive manufacturing (LAM) is a layer wise process used to fabricate the metal components by selectively fusing the powder using laser thermal energy [1,2]. Each layer is formed by overlapping of tracks results into a deposit. Direct metal laser sintering (DMLS), a LAM technique has widely been used for aerospace applications due to the obtained surface quality with minimal time in comparison of other AM techniques.
* Corresponding author. Tel.: +91 94519 92782; fax: +91 532 254 5341. E-mail address: [email protected] 2214-7853 © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the 9th International Conference of Materials Processing and Characterization, ICMPC-2019
T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
3843
18% Ni-300 Maraging steel (MS) is a Fe-Ni alloy with low carbon content offers an ultra-high strength. The ultra-high strength of MS is established by heat treatment (aging at 480 °C for 6 h) due to the intermetallic precipitates formed during aging [3,4]. Owing to the high σ/w ratio (strength to weight), its application is well suited for safety-critical parts. MS applications in aerospace includes the motor casings, landing gears, rocket and missile skins, slat tracks and engine components [5,6]. Few illustrations of MS parts are displayed in Fig. 1 (a-b). (a)
(b)
Fig.1. Maraging steel parts (a) Rocket motor casing and (b) Landing and take-off gears Extensive literature is published to control and optimize the LAM process parameters for attaining fully dense parts [5,7]. Bai et al., 2017 [7] reported the influence of selective laser melting (SLM) process parameters on the relative density of MS 300 to attain fully dense parts. They also reported the influence of solution and aging treatment on the mechanical behaviour of MS 300. The found the decrease in tensile properties with increase in elongation while increase (nearly 200 %) by aging treatment. Casalino et al., 2015 [5] explored the energy density role on the porosity and mechanical properties. The optimum energy density of 2.78 J/mm2 is found to be desired for fully dense parts (> 99%) and high mechanical properties. Several literature is published on the influence of laser scan path/direction on the tensile properties of LAM parts due to change in solidification time and generated porosity in the physical parts. Liu et al., 2011 [8] analysed the outcomes of laser scan path (single direction and cross-direction) on the microstructure and tensile properties of LAM Inconel 718. They reported the inhibition of columnar dendrites and formation of fine grain size in crossdirection scan pattern in comparison of single direction results in increase of mechanical properties. Moreover, transgranular mode of fracture in cross-direction leads to high ductile behaviour. Dai et al., 2017 [4] investigated the influence of scan pattern and melt pool configuration on microstructure and mechanical properties of SLM AlSi12 parts. They reported the remelting as an efficient method to eliminate the pores. Rashid et al., 2017 [9] explored the influence of scan strategy (single scan and double scan of each layer) on SLM 17-4PH stainless steel density and metallurgical properties. They reported the increase in hardness (~32 %) by double scan due to uniform distribution of martensite dominant phase. Carter et al., 2014 [10] observed the effect of the laser scan pattern on grain structure and cracking behaviour of SLM CM247LC Ni super alloy. They also reported HIP effect on the island scan pattern. The bi-modal grain structure was found with two distinct regions. Fine grains were found on the top surface and elongated columnar grains in the build direction. Recently, Bhardwaj et al., 2018 [2] reported the effect of bi-direction and cross-direction strategy on the DMLS MS. They reported the high tensile properties are achieved in cross-directional scan than bi-direction scan due to suppression of columnar grains formed.
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T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
From the previous studies it is manifested that the scan direction significantly affects the tensile behaviour of LAM parts due to the difference in produced melt-pool configuration and porosity. In this study, tensile properties and fractography is analysed to investigate the effect of adopted scan directions. This research facilitates the fabrication of high strength and ductile MS parts using DMLS. 2. Materials and method In this work, MS powder (near spherical shape) of particle size 15-45 μm is provided by EOS GmbH (Germany) as shown in Fig. 2. The powder morphology facilitates the proper fusion of MS powder leads to reduced porosity.
Fig. 2. EOS MS powder morphology. The chemical constituent of MS is listed in Table 1. The large amount of Ni (17-19 %) results in the formation of soft martensite structures during aging. The constituents of Mo, Ti and Al is added to enhance the intermetallic precipitates formation during aging. However, they result in reduction of martensitic temperature (200-300 °C). To suppress their effect on martensitic temperature, Co is added in the matrix. MS has an advantage over other steels owing to low amount of carbon that avoids the formation of TiC precipitates leads to decrease in impact strength, ductility and toughness.
Table 1. Chemical composition of EOS MS. Element
Ni
Co
Mo
Ti
Al
Cr, Cu
C
Mn, Si
P,S
Fe
Weight (%)
~18
~9
~4.8
~0.7
~0.10
≤0.5
≤0.03
≤0.1
≤0.01
Bal.
T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
3845
In this work, samples are fabricated on the mild steel substrate using the EOSINT M280 DMLS LAM system. The system is available at Central Tool Room and Training Centre (CTTC), Bhubaneswar, India equipped with Ytterbium fibre laser (wavelength of 1060 nm). It includes maximum laser power of 400 W, scan speed upto 7000 mm/s and laser beam diameter of 100-500 μm. The oxygen level is maintained at 1.6%. Prior to sample fabrication, the base plate is pre-heated at 40 °C. The selected process parameters for samples fabrication as listed in Table 2 are based on our previous study [2]. The selection of process parameters was based on the optimization for reduced porosity and producing crack-free parts. Table 2. Selected process parameters for sample fabrication. Parameter
Value
Laser power
285W
Scan speed
960 mm/s
Hatch spacing
0.11 mm
Powder layer thickness
0.04 mm
(b)
(a)
(c)
(d)
(e) 8
90° 12 0°
40
2
Fig. 3. (a) 0° and (b) 90° laser scan direction adopted, (c), (d) samples of 0° and 90° respectively and (e) schematic representation of tensile specimen in this study.
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T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
In this research, two different scan directions 0° and 90° are selected as presented in Fig. 3 (a) and (b) respectively. Corresponding fabricated samples surface are displayed in Fig. 3 (c) and (d). The schematic representation of Sub-size tensile sample according to ASTM E8-16a is presented in Fig. 3 (e). The first adopted strategy (0°) is bi-directional to the axis parallel to the loading axis of the tensile specimen (0°) and another is in perpendicular direction to the loading axis of the tensile specimen (90°). Tensile tests are conducted using a BiSS UTM of maximum 25 kN load capacity. Tensile properties (3 samples of each scan pattern) are investigated at a cross-head speed of 0.5 mm/min. Fractography of fractured tensile specimens are investigated using scanning electron microscopy (Carl Zeiss EVO 50 SEM). 3. Results and discussion 3.1 Tensile test The tensile tests for both scan directions are generated using uni-axial tensile test at room temperature as shown in below in Fig. 4. Near similar elastic behaviour is exhibited for both scan directions. The tensile properties (YS, UTS and El) are obtained as summarized in Table 3. The obtained results of 90° tensile properties are in range of wrought MS [13]. The higher tensile properties are observed in 90° scan direction results in a high ductile failure. However, scan line 0° direction exhibits lower UTS and ductility due to the variation in scan direction leads to change in melt pool configuration and generated porosity after fabrication [11].
Fig. 4. Engineering stress-strain curve for 0° and 90° scan directions.
T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
3847
Table 3. Summary of tensile properties obtained for both scan directions. Scan direction
Yield Strength
Ultimate Tensile Strength
Elongation
(MPa)
(MPa)
0°
720±15
983.5±47.3
13.5±1.6
90°
780±25
1021.6±28.0
19±0.7
Wrought
760-895
1000-1170
6-17
(%)
3.2 Fractography The fracture surface morphology for both scan direction is obtained as presented in Fig. 5. The 90° scan direction exhibited high elongation owing to the nucleation and micro-void coalescence. While 0° scanning, large size deep holes of size ~100-110 μm (2-3 times than 90° scanning i.e. ~35-45 μm) is observed. The presence of large size holes results in early crack formation and lower tensile properties. Both scan direction shows quasi cleavage ductile failure. DMLS MS using 90° scan direction has higher ductility i.e. 40.74 % than 0° and ~10 % than wrought specimen [12]. Fractography of 90° samples as shown in Fig. 5 (b) depicts small sized holes along melt pool boundaries results in high ductile failure. Both the scan directions show quasi cleavage ductile failure as shown in Fig. 4 (a) and (b). Due to the variation in scan direction, the morphology of pores generated during fabrication will differ the crack initiation mechanism during applied tensile force. The variation in tensile behaviour is due to the generated pores along melt pool boundaries. (b) (a) Large deep holes Small size holes
Fig. 5. Fractography of fractured tensile surface for scan direction (a) 0° and (b) 90°. 4. Conclusions This study explored the effect of two scan direction (bi-directional) on the tensile properties for DMLS fabricated MS. The scan pattern / direction is investigated to have a strong influence on the tensile properties of the fabricated parts. The tensile properties of DMLS 90° scan direction are found in the range of wrought MS and they are recommended for fabricating higher elongation MS parts. Further, residual pores and stresses in the physical parts,
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T. Bhardwaj and M. Shukla / Materials Today: Proceedings 18 (2019) 3842–3848
post processing such as shot peening can be performed. The pore size of fabricated parts can be further reduced by aging treatment and hot isostatic pressing. Acknowledgements Thanks are largely due to Mr. A.B. Nayak of Central Tool Room and Training Center, Bhubaneswar, India for extending the DMLS facilities. One of the author Tarun Bhardwaj would like to thank the Ministry of Human Resource Development (MHRD), Government of India for financial assistance. References [1] I. Gibson, D.W. Rosen, B. Stucker, Additive Manufacturing Technologies: rapid Prototyping to Direct Digital Manufacturing, Springer, 2009, pp. 1-14. [2] T. Bhardwaj, M. Shukla, Effect of laser scanning strategies on texture, physical and mechanical properties of laser sintered maraging steel, Mat. Sci. Eng. A 734 (2018) 102-109. [3] A.G. Demir, B. Previtali, Investigation of remelting and preheating in SLM of 18Ni300 maraging steel as corrective and preventive measures for porosity reduction, Int. J. Adv. Manuf. Technol. 93 (2017) 2697-2709. [4] D. Dai, D. Gu, H. Zhang, J. Xiong, C. Ma, C. Hong, and R. Poprawe, Influence of scan strategy and molten pool configuration on microstructures and tensile properties of selective laser melting additive manufactured aluminum based parts, Opt. Laser Technol., 99, 91-100 (2018). [5] G. Casalino, S.L. Campanelli, N. Contuzzi, A.D. Ludovico, Experimental investigation and statistical optimization of the selective laser melting process of a maraging steel, Opt. Laser Technol. 65 (2015) 151-158. [6] T.H. Becker, D. Dimitrov, The achievable mechanical properties of SLM produced maraging Steel 300 components, Rapid Prototyping J 22 (2016) 487-494. [7] Y. Bai, Y. Yang, D. Wang, M. Zhang, Influence mechanism of parameters process and mechanical properties evolution mechanism of maraging steel 300 by selective laser melting, Mat. Sci. Eng. A 703 (2017) 116-123. [8] F. Liu, X. Lin, C. Huang, M. Song, G. Yang, J. Chen, W. Huang, The effect of laser scanning path on microstructures and mechanical properties of laser solid formed nickel-base superalloy Inconel 718, J. Alloys Comp. 509 (2011) 4505–4509. [9] R. Rashid, S.H. Masood, D. Ruan, S. Palanisamy, R.A. Rahman Rashid, M. Brandt, Effect of scan strategy on density and metallurgical properties of 17-4PH parts printed by Selective Laser Melting (SLM), J. Mater. Process Tech. 249 (2017) 502-511. [10] L.N. Carter, C. Martin, P.J. Withers, M.M. Attallah, The influence of the laser scan strategy on grain structure and cracking behaviour in SLM powder-bed fabricated nickel superalloy, J. Alloys Comp. 615 (2014) 338–347. [11] A. Kudzal, B. McWilliams, C. Hofmeister, F. Kellogg, J. Yu, J.T. Scarff, J. Liang, Effect of scan pattern on the microstructure and mechanical properties of Powder bed Fusion additive manufactured 17-4 stainless steel, Mater. Design 133 (2017) 205-215. [12] M.N. Rao, Progress in understanding the metallurgy of 18 % nickel maraging steels, Int. J. Mater. Res., 97 (2006) 1594-1607.