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Selective laser melting helps fabricate record-large bulk metallic glass: Experiments, simulation and demonstrative part
Journal Pre-proof Selective laser melting helps fabricate record-large bulk metallic glass: Experiments, simulation and demonstrative part Liang Wang, Hao Wang, Yingkuo Liu, Zhongxue Fu, Taijiang Peng, Jun Shen, Suyuan Zhou, Ming Yan, Gang Wang, Yuhong Dai PII:
S0925-8388(19)32964-0
DOI:
https://doi.org/10.1016/j.jallcom.2019.151731
Reference:
JALCOM 151731
To appear in:
Journal of Alloys and Compounds
Received Date: 16 May 2019 Revised Date:
18 July 2019
Accepted Date: 5 August 2019
Please cite this article as: L. Wang, H. Wang, Y. Liu, Z. Fu, T. Peng, J. Shen, S. Zhou, M. Yan, G. Wang, Y. Dai, Selective laser melting helps fabricate record-large bulk metallic glass: Experiments, simulation and demonstrative part, Journal of Alloys and Compounds (2019), doi: https:// doi.org/10.1016/j.jallcom.2019.151731. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
Selective laser melting helps fabricate record-large bulk metallic glass: Experiments, simulation and demonstrative part Liang Wanga,b§, Hao Wanga§ , Yingkuo Liua, Zhongxue Fua, Taijiang Penga*, Jun Shena, Suyuan Zhoub,Gang Wangc, Yuhong Daid, Ming Yanb* a
Guangdong Provincial Key Laboratory of Micro/Nano Optomechatronics
Engineering, College of Mechatronics and Control Engineering, Shenzhen University, Shenzhen, 518060, China b
Department of Materials Science and Engineering, and Shenzhen Key Laboratory
for Additive Manufacturing of High-performance Materials, Southern University of Science and Technology, Shenzhen 518055, China c
Shanghai University, Laboratory for Microstructures, Institute of Materials, Shanghai, 20044, China
d
Shenzhen Sunshine Laser & Electronics Technology Co., 518057, Shenzhen, China *
Corresponding authors: [email protected]; [email protected] §
These two authors contribute equally to this work.
Abstract: Size limitation is one of the bottleneck issues to bulk metallic glasses (BMGs). Selective laser melting (SLM) uses localized, point-specific, high energy beam to manufacture. By applying SLM to an Fe-based BMG, a record-large, fully amorphous sample (Ø45 mm × 20 mm) has been produced into good mechanical properties. SLM process map is constructed and finite element simulation is employed for the study. The rapid cooling rate during SLM, a sufficiently short exposure time to 1
high temperature, and the good thermal stability of the alloy are the key points to form such superlarge, quality BMG. As-printed, demonstrative part is present, and the implications of the results are addressed.
Keywords: Selective laser melting, Bulk metallic glass, Size limitation, Finite element simulation
1.
Introduction
Metallic glass (MG) was firstly discovered in the 1960s [1]. Over the past five decades, intensive research efforts have been made to understand the material, and significant progress has been made. Now various applicants are starting to emerge, by making good use of MGs’ wonderful properties such as excellent corrosion resistance and wear resistance, high hardness, doubled or even tripled fracture strength of their crystalline counterparts, and/or their outstanding magnetic properties [2–4].
Albeit the advanced properties, on a whole MGs suffer at least several big limitations. Each alloy composition has a specific glass forming ability (GFA), a critical cooling rate (Rc) to retain amorphous structure during solidification, and a corresponding critical size (dc). Small dc is one of the major drawbacks. To obtain large dc is not an easy task. Only until recently, bulk metallic glasses (when dc > 1 mm) are realized in all major alloy systems. Taking the relatively low cost Fe-based BMGs as examples, the Fe68.3C6.9Si2.5B6.7Cr2.3Mo2.1 (at.%) BMG was made into Ø4 mm rod by 2
water-cooled suction casting [5]. Lu et al. [6] and Ponnambalam et al.[7] reported 12 mm thick FeCr(Co)MoMnCB BMGs. Shen et al. [8] increased the critical size to Ø16 mm with the FeCoCrMoCBY alloy system using copper mould suction casting. This is probably the largest Fe-based BMG developed so far, and it took people ~20 years to achieve it. Meanwhile, to those conventional processing techniques such as copper mould casting, it will be rather difficult to make further larger BMGs due to the limited cooling rates associated with them, although larger BMGs are always needed to meet with ever increasing demand on the materials.
Additive
manufacturing
(AM)
allows
direct,
mouldless
fabrication
of
complex-geometry and good-quality parts [9]. Selective laser melting (SLM) [10] is one of the mainstream AM techniques. It uses highly collimated, high power laser beam to melt metal powder in a layer-by-layer manner, during which metallurgical bonding between molten materials forms. Since a fast laser scan and an infinite heat conduction are almost always associated with SLM, the corresponding cooling rate is often rather high, reaching ~104-106 K/s [11,12]. Such high cooling rate will be sufficient to ensure an amorphous structure in most cases, if the BMGs to be fabricated are of good GFA as well as good thermal stability. The latter is also important, because during the SLM processing, aside from the molten pools, there will be heat affected zones where crystallization may occur. Nevertheless, because of the merits of SLM, there have been research activities to explore its feasibility to fabricate BMGs. Shortcomings in the previous studies include [13–15]: (a) low 3
relative density and high concentration of defects like pores, and/or (b) (crystalline+amorphous) composite microstructure instead of pure amorphous state, and/or (c) limited critical size (e.g. ~ 3 mm). In a very recent study by Mahbooba et al. [16], the Direct Metal Laser Sintering (DMLS) technique was used for fabricating large Fe-based BMG materials, but the resultant microstructure was not fully amorphous.
In order to provide superlarge and high-quality Fe-based BMGs for the various applications such as the mobile industry, a systematic investigation has been conducted by this study on an Fe55Cr25Mo16B2C2 BMG. We will show that, through our research efforts in terms of alloy selection, SLM processing optimization and computer simulation, we have successfully fabricated a record-large Fe-based BMG (Ø45 mm × 20 mm). The as-printed microstructure stays in a fully amorphous state, and good relative density has been realized. The nanohardness of the BMG is 14 GPa high. We have further clarified that high cooling rate and ms-scale short period of exposure time to high temperature ensure the amorphous structure. SLM-prepared 36-teeth gear is provided for demonstration purpose. Implications of the findings will be discussed.
2.
Materials and methods
The as-purchased Fe55Cr25Mo16B2C2 BMG powder was used for the study; the alloy has a dc of ~ 3 mm, a supercooled liquid region (∆Tx) of 50 K, and crystallization 4
temperature (Tx) of ~ 883 K. The SLM facility used was an M2 cusing 3D printer, equipped with an Nd:YAG fiber laser. The closed build chamber was protected by high purity argon so that the oxygen content during printing was less than 100 ppm. Laser power ranging from 100 W to 300 W and scanning speed ranging from 300 mm/s to 1000 mm/s were used to explore optimal processing parameters, while layer thickness h (= 30 µm) and hatch spacing t (= 105 µm) were kept as constants. The substrate was kept at room temperature during printing. The relative density of the SLM specimens was calculated by comparing it with cast ingot (density=7.55 g/cm3).
The particle size of the powder was analyzed by a laser particle size analyzer (Malvern, Mastersizer 3000, United Kingdom). The surface morphology of the powder and the as-printed microstructure were analyzed using scanning electron microscope (SEM, FEI Quanta FEG 450). X-ray diffraction (XRD, MiniFlex 600) was conducted for phase analysis. Transmission electron microscopy (TEM, JEM-2010F, 200 kV) was used to detail the microstructure; the TEM samples were prepared using a focused ion beam (FIB, FEI Scios). High temperature differential scanning calorimeter (DSC, STA 8000) in a constant-rate heating mode (20 K/min) was used for thermal analysis. To check the amorphous status of the as-printed samples, three sample pieces from the upper, middle and lower locations of the Ø45 mm × 20 mm bulk sample was cut and analyzed. Nano-indentation (HYSIRON TI 950 Tribo Indenter) was used to evaluate the hardness; 12 sets of data from randomly-selected different areas of the polished sample (Ø12 mm × 6.5 mm, cut 5
from center of the as-printed BMG) were acquired and then averaged. The bulk mechanical properties of BMG were obtained by micropillar compression. The pillars (Ø1.5 µm × 3 µm) were prepared using FIB and tested by nano-indentation, which used a Flat Ended Conical (Nominal Flat Diameter of 10 µm) indenter whose Young's modulus is 1140 GPa and Poisson's ratio is 0.07, respectively.
3. Numerical simulation A finite element method (FEM) was used to analyze the full-scale temperature field and help understand the experimental results. It adopted a layer wise AM model using COMSOL Multiphysics 5.3a commercial software. The full-scale AM physical model was based on the governing behavior of conductive heat transfer in the track-by-track and layer-wise printing manner, see Complementary Materials and the corresponding Table S1 and Table S2.
4. Results Fig. 1(a) shows an SEM image of the spherical Fe55Cr25Mo16B2C2 BMG powder. Powder particle size analysis shows Dv (10) at 20.7 µm, Dv (50) at 34.7 µm, and Dv (90) at 65.8 µm. Fig. 1(b) shows a camera-snapshot image of the as-printed samples for exploring optimal SLM parameters. After systematic SLM experiments, a process map has been determined as the one shown in Fig. 1(c). Regions of ‘difficult to form’, ‘cracks’, ‘crystallization’ and ‘amorphous’ have been notified. The parameters for forming amorphous structure are pinpointed, where the laser powers are determined 6
as 100-300 W and scanning speeds are determined as 300-1000 mm/s. Such wide amorphous formation area suggests an excellent formability of the BMG by SLM. Furthermore, when the laser power is 100 W and the scanning rate is 300 mm/s (corresponding energy density = 105.8 J/mm3), the as-printed part is close to fully dense, reaching relative density of >99.0% and free of macroscopic defects like wrapping. It needs to mention that amorphous state of the as-printed samples is checked by both XRD and DSC. Fig. 1(d) provides a few typical examples, showing good parameters for forming amorphous state (e.g. 100 W and 400 mm/s) and the parameters that lead to more crystalline phases in the microstructure (e.g. 180 W and 600 mm/s). The BMG powder has been used as a reference as the fully amorphous state.
Based on the optimized SLM parameters, superlarge samples have been printed, Fig. 1(e). The largest ones are up to Ø45 mm × 20 mm. It is noted that their surface quality is good and macro delamination is not observable. In order to check the microstructure, XRD analysis is firstly conducted, confirming the bottom, the center and the top surface all staying in the amorphous states, Fig. 1(f). TEM is further employed and the typical results are shown in Fig. 1(g). Both the TEM bright field image and the selected area electron diffraction (SAED) pattern verify an amorphous structure, showing no phase contrast and only diffuse halo rings in Fig. 1(g) [2,17]. Thermal properties of the powder and the as-printed BMG sample have been subsequently compared using DSC. As shown in Fig. 1(h), it is measured that both 7
materials show the glass transition temperature Tg at ~833 K and the crystallization temperature Tx at ~ 883 K. Comparing exothermic enthalpy ∆H of the as-printed sample (= 67.73 J/g) with the amorphous powder (= 68.27 J/g), the corresponding ratio is ~99.21%, confirming a nearly full amorphous structure.
Furthermore, the mechanical properties of Fe-based BMG are evaluated. Nano-indentation curves are shown in Fig. 2(a), revealing an average nano-hardness of 14 GPa (Fig. 2b). The corresponding Vickers hardness is about 1260 HV. Such hardness is even higher than that of the Directed Metal Laser Sintering sample (~902 HV), supersonic plasma spraying coatings (1005 HV) or the atmospheric plasma spraying specimen (731±77 HV) of similar alloy compositions [16,18,19]. Micropillar compression has been further used to evaluate the fracture strength of as-printed BMG. Fig. 2(c) and (d) show the typical SEM images of the micropillar before and after compression. Fig. 2(e) shows the stress-strain curve. A few “pop-ins” are observable from the curve, implying that microfracture may have occurred during the loading procedure, which phenomenon is usually associated with brittle materials [20]. The yield strength of the as-printed BMG is ~4500 MPa. Furthermore, a micrograph is shown in Fig. 2(f), showing that microcracks may exist on some areas of the as-printed BMG. Such microscopic defects may have reduced the mechanical properties of the as-printed material [21].
Fig. 3(a) presents the FEM simulation results for the SLM processing, showing a 8
transient temperature profile for the molten pool and surrounding areas. The fiber laser for the SLM processing projects a near Gaussian TEM00 light onto the metal powder, showing its most intensity in the beam center and leading to a maximum temperature of ~ 2.34×103 K in the area directly beneath the beam. Considering that SLM is close to an infinite heat conduction, the cooling rate in the molten pool area (e.g. P1 in the figure) is ~1.38×106 K/s high. This is several orders larger than the critical cooling rate needed for forming amorphous structure (~ 549 K/s), guaranteeing an amorphous state [22]. Aside from the molten pool, in order to retain a bulk amorphous structure, temperatures and cooling rates of other areas in the as-printed sample are also critically important, such as those in the heat affected zone. Typical results for those areas are also shown in Fig. 3, when assuming their positions are ~150 µm (P2) and ~200 µm (P3), respectively, away from the beam center. The corresponding temperature-time variation is shown in Fig. 3(b). Critical temperature parameters, namely the Tg, Tx and Tm (=1423 K), of the BMG are shown in dotted lines in Fig. 3(b). It is noted that, although the temperature in the heat affected zone (P2) can be higher than Tx, the corresponding time window / lifetime of the high temperature period is rather short, i.e. ~0.8 ms. During this period of time, in theory the crystallization is possible to occur, but, in reality, an incubation period is required which needs ~1.87 ms [23]. Nucleation in this case cannot complete and amorphous structure remains due to the kinetic factor. Far end areas (e.g. P3) experience temperature rise that is lower than the Tg temperature, leading to no crystallization. The overall simulation results are therefore consistent with the XRD and TEM 9
characterizations in Fig. 1.
As shown in Fig. 4(a), development of the Fe-based BMGs from year 1995 to present is given in terms of the critical size obtained (in mm) and the corresponding time [8,24–32]. It is noted that, in the past 20 years (1995-2018), great progress has been made in terms of developing BMGs with larger critical sizes and better GFAs. The largest, fully amorphous Fe-based BMG, however, is still limited to ~ 16 mm by using conventional processing pathways, despite the two-decade intensive research efforts. In contrast, our current study presents that, by making good use of the unique characteristics of SLM, one can conveniently make amorphous Fe-based BMGs up to (Ø45 mm× 20 mm) large, achieving the best result so far.
Aside from making superlarge BMGs, another important advantage of SLM lies in its capability to make complex geometry part without the need of premade mould. This makes it appealing in manufacturing customized product such as the 36-teech gears as shown in Fig. 4(b). It demonstrates the capability of SLM to manufacture customer-designed, complex-geometry and large-sized BMG products.
5. Brief discussion To form superlarge BMGs is a challenging but rewarding task. Conventional methods such as copper mould casting can achieve cooling rate of 102-103 K/s and realize critical sizes of ~15 mm for Fe-based BMGs. Larger sized BMGs, however, require 10
novel technologies for providing sufficiently high cooling rate across the whole bulk sample. SLM is such technique. It delivers highly-localized, high-intensity and fast-scanned laser beam to melt metal powders, during which process the following criteria for retaining the amorphous structure are simultaneously satisfied: (a) A sufficiently high cooling rate during solidification to ensure an amorphous state to form, and (b) a sufficiently low-temperature environment to avoid subsequent crystallization, or a sufficiently short period of exposure time to temperatures higher than the corresponding Tg/Tx temperature. The current study confirms these by both experimental verification and computer simulation analysis. It implies that it is feasible to use SLM to fabricate large BMG products for the various industries.
6. Conclusion We report a record-large Fe-based BMG (Ø45 mm × 20 mm) that has been fabricated by SLM. The as-printed Fe55Cr25Mo16B2C2 BMG shows amorphous structure with evidences from XRD, DSC, TEM and FEM simulation. It presents high relative density (~ 99.0%), large nanohardness (14 GPa) and high yield strength (~4500 MPa). It is clarified that the lifetime of the molten pool is at the ms scale, corresponding to a rapid cooling rate of ~1.38×106 K/s. During printing, other locations of the sample experience either low temperatures (< Tg) or very short exposure time to high heat input, therefore avoiding crystallization due to thermodynamic and/or kinetic reasons and ensuring an amorphous structure across the whole as-printed sample. Demonstrative 36-teech gear part is present, implying that SLM may open up the 11
applications of BMGs by providing superlarge sized, customer-designed, quality parts.
Acknowledgments This work was supported by National Natural Science Foundation of China (Grant No.51771123) and the Shenzhen Peacock Innovation Project (Grant No. KQJSCX20170327151307811, KQJSCX20160226174209). Dr M. Yan appreciates the support by the Humboldt Research Fellowship for Experienced Researchers.
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References [1]
W. Klement, R. Willens, P. Duwez, © 1960 Nature Publishing Group, Nat. No. 4740. 187 (1960) 896–870. doi:10.1038/scientificamerican0268-74.
[2]
Y. Wang, J. Zhang, K. Wu, G. Liu, D. Kiener, J. Sun, Nanoindentation creep behavior of Cu–Zr metallic glass films, Mater. Res. Lett. 6 (2018) 22–28. doi:10.1080/21663831.2017.1383946.
[3]
W.H. Wang, R.J. Wang, F.Y. Li, D.Q. Zhao, M.X. Pan, Elastic constants and their pressure dependence of Zr41Ti14Cu12.5Ni9Be 22.5C1 bulk metallic glass, Appl. Phys. Lett. 74 (1999) 1803–1805. doi:10.1063/1.123091.
[4]
X.M. Huang, C.T. Chang, Z.Y. Chang, A. Inoue, J.Z. Jiang, Glass forming ability, mechanical and magnetic properties in Fe-W-Y-B alloys, Mater. Sci. Eng., A . 527 (2010) 1952–1956. doi:10.1016/j.msea.2009.11.042.
[5]
H. Li, S. Yi, Fabrication of bulk metallic glasses in the alloy system Fe-C-Si-B-P-Cr-Mo-Al using hot metal and industrial ferro-alloys, Mater. Sci. Eng. A. 448–451 (2007) 189–192. doi:10.1016/j.msea.2006.02.262.
[6]
Z.P. Lu, C.T. Liu, J.R. Thompson, W.D. Porter, Structural amorphous steels, Phys. Rev. Lett. 92 (2004) 1–4. doi:10.1103/PhysRevLett.92.245503.
[7]
V. Ponnambalam, S.J. Poon, G.J. Shiflet, Fe-Mn-Cr-Mo-(Y,Ln)-C-B (Ln = Lanthanides) bulk metallic glasses as formable amorphous steel alloys, J. Mater. Res. 19 (2004) 3046–3052. doi:10.1557/JMR.2004.0374.
[8]
J. Shen, Q. Chen, J. Sun, H. Fan, G. Wang, Exceptionally high glass-forming ability of an FeCoCrMoCBY alloy, Appl. Phys. Lett. 86 (2005) 1–3. 13
doi:10.1063/1.1897426. [9]
J.J. Yan, D.L. Zheng, H.X. Li, X. Jia, J.F. Sun, Y.L. Li, M. Qian, M. Yan, Selective laser melting of H13: microstructure and residual stress, J. Mater. Sci. 52 (2017) 12476–12485. doi:10.1007/s10853-017-1380-3.
[10] R. Laquai, B.R. Müller, G. Kasperovich, J. Haubrich, G. Requena, G. Bruno, X-ray refraction distinguishes unprocessed powder from empty pores in selective laser melting Ti-6Al-4V, Mater. Res. Lett. 6 (2018) 130–135. doi:10.1080/21663831.2017.1409288. [11] F. Audebert, R. Colaço, R. Vilar, H. Sirkin, Production of glassy metallic layers by laser surface treatment, Scr. Mater. 48 (2003) 281–286. doi:10.1016/S1359-6462(02)00382-2. [12] S. Katakam, J.Y. Hwang, S. Paital, R. Banerjee, H. Vora, N.B. Dahotre, In situ laser synthesis of Fe-based amorphous matrix composite coating on structural steel, Metall. Mater. Trans. A Phys. Metall. Mater. Sci. 43 (2012) 4957–4966. doi:10.1007/s11661-012-1312-4. [13] Y. Wang, G. Li, Z. Shi, M. Liu, X. Zhang, Y. Liu, Effects of graphite addition on the microstructure and properties of laser cladding Zr-Al-Ni-Cu amorphous coatings, J. Alloys Compd. 610 (2014) 713–717. doi:10.1016/j.jallcom.2014.05.009. [14] D. Ouyang, N. Li, W. Xing, J. Zhang, L. Liu, 3D printing of crack-free high strength Zr-based bulk metallic glass composite by selective laser melting, Intermetallics. 90 (2017) 128–134. doi:10.1016/j.intermet.2017.07.010. 14
[15] S. Pauly, L. Löber, R. Petters, M. Stoica, S. Scudino, U. Kühn, J. Eckert, Processing metallic glasses by selective laser melting, Mater. Today. 16 (2013) 37–41. doi:10.1016/j.mattod.2013.01.018. [16] Z. Mahbooba, L. Thorsson, M. Unosson, P. Skoglund, H. West, T. Horn, C. Rock, E. Vogli, O. Harrysson, Additive manufacturing of an iron-based bulk metallic glass larger than the critical casting thickness, Appl. Mater. Today. 11 (2018) 264–269. doi:10.1016/j.apmt.2018.02.011. [17] C. Zhang, L. Liu, K.C. Chan, Q. Chen, C.Y. Tang, Wear behavior of HVOF-sprayed Fe-based amorphous coatings, Intermetallics. 29 (2012) 80–85. doi:10.1016/j.intermet.2012.05.004. [18] Y. An, G. Hou, J. Chen, X. Zhao, G. Liu, H. Zhou, J. Chen, Microstructure and tribological properties of iron-based metallic glass coatings prepared by atmospheric plasma spraying, Vacuum. 107 (2014) 132–140. doi:10.1016/j.vacuum.2014.04.021. [19] Y. yang Zhou, G. zheng Ma, H. dou Wang, G.L. Li, S. ying Chen, H. jun Wang, Ming-Liu, Fabrication and characterization of supersonic plasma sprayed Fe-based amorphous metallic coatings, Mater. Des. 110 (2016) 332–339. doi:10.1016/j.matdes.2016.08.003. [20] C.A. Schuh, T.G. Nieh, A nanoindentation study of serrated flow in bulk metallic glasses, Acta Mater. 51 (2003) 87–99. doi:10.1016/S1359-6454(02)00303-8. [21] N. Li, J. Zhang, W. Xing, D. Ouyang, L. Liu, 3D printing of Fe-based bulk 15
metallic glass composites with combined high strength and fracture toughness, Mater. Des. 143 (2018) 285–296. doi:10.1016/j.matdes.2018.01.061. [22] Y. Huang, Y. Guo, H. Fan, J. Shen, Synthesis of Fe–Cr–Mo–C–B amorphous coating with high corrosion resistance, Mater. Lett. 89 (2012) 229–232. doi:10.1016/J.MATLET.2012.08.114. [23] D. Ouyang, W. Xing, N. Li, Y. Li, L. Liu, Structural evolutions in 3D-printed Fe-based metallic glass fabricated by selective laser melting, Addit. Manuf. 23 (2018) 246–252. doi:10.1016/j.addma.2018.08.020. [24] A. Inoue, Y. Shinohara, J.S. Gook, Thermal and Magnetic Properties of Bulk Fe-Based Glassy Alloys Prepared by Copper Mold Casting, Mater. Trans. JIM. 36 (1995) 1427–1433. doi:10.2320/matertrans1989.36.1427. [25] A. Inoue, T. Zhang, A. Takeuchi, Bulk amorphous alloys with high mechanical strength and good soft magnetic properties in Fe-TM-B (TM=IV-VIII group transition metal) system, Appl. Phys. Lett. 71 (1997) 464–466. doi:10.1063/1.119580. [26] B. Shen, H. Koshiba, H. Kimura, A. Inoue, High Strength and Good Soft Magnetic Properties of Bulk Glassy Fe–Mo–Ga–P–C–B Alloys with High Glass-Forming Ability, Mater. Trans. JIM. 41 (2000) 1478–1481. doi:10.2320/matertrans1989.41.1478. [27] V. Ponnambalam, S.J. Poon, G.J. Shiflet, V.M. Keppens, R. Taylor, G. Petculescu, Synthesis of iron-based bulk metallic glasses as nonferromagnetic 16
amorphous steel alloys, Appl. Phys. Lett. 83 (2003) 1131–1133. doi:10.1063/1.1599636. [28] V. Ponnambalam, S.J. Poon, G.J. Shiflet, Fe-based bulk metallic glasses with diameter thickness larger than one centimeter, J. Mater. Res. 19 (2004) 1320–1323. doi:10.1557/jmr.2004.0176. [29] K. Amiya, A. Inoue, Fe-(Cr,Mo)-(C,B)-Tm Bulk Metallic Glasses with High Strength and High Glass-Forming Ability, Mater. Trans. 47 (2006) 1615–1618. doi:10.2320/matertrans.47.1615. [30] A. Makino, T. Kubota, M. Makabe, C.T. Chang, A. Inoue, FeSiBP metallic glasses with high glass-forming ability and excellent magnetic properties, Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 148 (2008) 166–170. doi:10.1016/j.mseb.2007.09.010. [31] R. Nowosielski, R. Babilas, Glass-forming ability analysis of selected Fe-based bulk amorphous alloys, 42 (2010) 66–72. [32] P.H. Tsai, A.C. Xiao, J.B. Li, J.S.C. Jang, J.P. Chu, J.C. Huang, Prominent Fe-based bulk amorphous steel alloy with large supercooled liquid region and superior corrosion resistance, J. Alloys Compd. 586 (2014) 94–98. doi:10.1016/j.jallcom.2013.09.186.
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Figures caption Fig. 1 (a) SEM image of the amorphous alloy powder; figure inset shows the particle size distribution, (b) the as-printed samples for exploring optimal SLM parameters, (c) SLM processing map showing different characteristic areas. Different colors and different marks are used for highlighting the regions processed by varying laser powers and scanning speeds. Among these, the ‘amorphous’ region denotes that the as-printing microstructure are amorphous, ‘difficult to form’ means difficult to form a complete build, ‘crystallization’ refers to crystalized microstructure, ‘cracks’ refer to serious cracking, and ‘near full density’ means sample of >99% relative density, (d) the DSC curve of the original powder and three typical as-printed samples, (e) camera snapshot images of the 3D printed superlarge samples, (f) XRD pattern of the powder and superlarge sample slices of different locations, (g) TEM bright field image and the corresponding SAED pattern of the as-printed sample (sample from center location of the as-printed material), and (h) DSC analysis of the amorphous powder and the as-printed sample (sample from center location of the as-printed material).
Fig. 2 (a) Nano-indentation curves, and (b) nano-hardness of the as-printed sample (the test area was randomly selected), (c) and (d) show the typical SEM images of the micropillar before and after compression, (e) the stress-strain curve for the micro-compression sample, and (f) the cross-sectional microscopies of the BMG.
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Fig. 3 (a) Transient temperature field during the SLM processing determined by finite element simulation analysis, and (b) the temperature-time profiles of the molten pool (P1), heat affected zone (P2), and far site area (P3).
Fig. 4 (a) Development of Fe-based BMGs in term of their critical sizes, and (b) camera snapshot of an SLM-prepared 36-teech gear (tip circle diameter of 41.5 mm).
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S0925-8388(19)32964-0
DOI:
https://doi.org/10.1016/j.jallcom.2019.151731
Reference:
JALCOM 151731
To appear in:
Journal of Alloys and Compounds
Received Date: 16 May 2019 Revised Date:
18 July 2019
Accepted Date: 5 August 2019
Please cite this article as: L. Wang, H. Wang, Y. Liu, Z. Fu, T. Peng, J. Shen, S. Zhou, M. Yan, G. Wang, Y. Dai, Selective laser melting helps fabricate record-large bulk metallic glass: Experiments, simulation and demonstrative part, Journal of Alloys and Compounds (2019), doi: https:// doi.org/10.1016/j.jallcom.2019.151731. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.
Selective laser melting helps fabricate record-large bulk metallic glass: Experiments, simulation and demonstrative part Liang Wanga,b§, Hao Wanga§ , Yingkuo Liua, Zhongxue Fua, Taijiang Penga*, Jun Shena, Suyuan Zhoub,Gang Wangc, Yuhong Daid, Ming Yanb* a
Guangdong Provincial Key Laboratory of Micro/Nano Optomechatronics
Engineering, College of Mechatronics and Control Engineering, Shenzhen University, Shenzhen, 518060, China b
Department of Materials Science and Engineering, and Shenzhen Key Laboratory
for Additive Manufacturing of High-performance Materials, Southern University of Science and Technology, Shenzhen 518055, China c
Shanghai University, Laboratory for Microstructures, Institute of Materials, Shanghai, 20044, China
d
Shenzhen Sunshine Laser & Electronics Technology Co., 518057, Shenzhen, China *
Corresponding authors: [email protected]; [email protected] §
These two authors contribute equally to this work.
Abstract: Size limitation is one of the bottleneck issues to bulk metallic glasses (BMGs). Selective laser melting (SLM) uses localized, point-specific, high energy beam to manufacture. By applying SLM to an Fe-based BMG, a record-large, fully amorphous sample (Ø45 mm × 20 mm) has been produced into good mechanical properties. SLM process map is constructed and finite element simulation is employed for the study. The rapid cooling rate during SLM, a sufficiently short exposure time to 1
high temperature, and the good thermal stability of the alloy are the key points to form such superlarge, quality BMG. As-printed, demonstrative part is present, and the implications of the results are addressed.
Keywords: Selective laser melting, Bulk metallic glass, Size limitation, Finite element simulation
1.
Introduction
Metallic glass (MG) was firstly discovered in the 1960s [1]. Over the past five decades, intensive research efforts have been made to understand the material, and significant progress has been made. Now various applicants are starting to emerge, by making good use of MGs’ wonderful properties such as excellent corrosion resistance and wear resistance, high hardness, doubled or even tripled fracture strength of their crystalline counterparts, and/or their outstanding magnetic properties [2–4].
Albeit the advanced properties, on a whole MGs suffer at least several big limitations. Each alloy composition has a specific glass forming ability (GFA), a critical cooling rate (Rc) to retain amorphous structure during solidification, and a corresponding critical size (dc). Small dc is one of the major drawbacks. To obtain large dc is not an easy task. Only until recently, bulk metallic glasses (when dc > 1 mm) are realized in all major alloy systems. Taking the relatively low cost Fe-based BMGs as examples, the Fe68.3C6.9Si2.5B6.7Cr2.3Mo2.1 (at.%) BMG was made into Ø4 mm rod by 2
water-cooled suction casting [5]. Lu et al. [6] and Ponnambalam et al.[7] reported 12 mm thick FeCr(Co)MoMnCB BMGs. Shen et al. [8] increased the critical size to Ø16 mm with the FeCoCrMoCBY alloy system using copper mould suction casting. This is probably the largest Fe-based BMG developed so far, and it took people ~20 years to achieve it. Meanwhile, to those conventional processing techniques such as copper mould casting, it will be rather difficult to make further larger BMGs due to the limited cooling rates associated with them, although larger BMGs are always needed to meet with ever increasing demand on the materials.
Additive
manufacturing
(AM)
allows
direct,
mouldless
fabrication
of
complex-geometry and good-quality parts [9]. Selective laser melting (SLM) [10] is one of the mainstream AM techniques. It uses highly collimated, high power laser beam to melt metal powder in a layer-by-layer manner, during which metallurgical bonding between molten materials forms. Since a fast laser scan and an infinite heat conduction are almost always associated with SLM, the corresponding cooling rate is often rather high, reaching ~104-106 K/s [11,12]. Such high cooling rate will be sufficient to ensure an amorphous structure in most cases, if the BMGs to be fabricated are of good GFA as well as good thermal stability. The latter is also important, because during the SLM processing, aside from the molten pools, there will be heat affected zones where crystallization may occur. Nevertheless, because of the merits of SLM, there have been research activities to explore its feasibility to fabricate BMGs. Shortcomings in the previous studies include [13–15]: (a) low 3
relative density and high concentration of defects like pores, and/or (b) (crystalline+amorphous) composite microstructure instead of pure amorphous state, and/or (c) limited critical size (e.g. ~ 3 mm). In a very recent study by Mahbooba et al. [16], the Direct Metal Laser Sintering (DMLS) technique was used for fabricating large Fe-based BMG materials, but the resultant microstructure was not fully amorphous.
In order to provide superlarge and high-quality Fe-based BMGs for the various applications such as the mobile industry, a systematic investigation has been conducted by this study on an Fe55Cr25Mo16B2C2 BMG. We will show that, through our research efforts in terms of alloy selection, SLM processing optimization and computer simulation, we have successfully fabricated a record-large Fe-based BMG (Ø45 mm × 20 mm). The as-printed microstructure stays in a fully amorphous state, and good relative density has been realized. The nanohardness of the BMG is 14 GPa high. We have further clarified that high cooling rate and ms-scale short period of exposure time to high temperature ensure the amorphous structure. SLM-prepared 36-teeth gear is provided for demonstration purpose. Implications of the findings will be discussed.
2.
Materials and methods
The as-purchased Fe55Cr25Mo16B2C2 BMG powder was used for the study; the alloy has a dc of ~ 3 mm, a supercooled liquid region (∆Tx) of 50 K, and crystallization 4
temperature (Tx) of ~ 883 K. The SLM facility used was an M2 cusing 3D printer, equipped with an Nd:YAG fiber laser. The closed build chamber was protected by high purity argon so that the oxygen content during printing was less than 100 ppm. Laser power ranging from 100 W to 300 W and scanning speed ranging from 300 mm/s to 1000 mm/s were used to explore optimal processing parameters, while layer thickness h (= 30 µm) and hatch spacing t (= 105 µm) were kept as constants. The substrate was kept at room temperature during printing. The relative density of the SLM specimens was calculated by comparing it with cast ingot (density=7.55 g/cm3).
The particle size of the powder was analyzed by a laser particle size analyzer (Malvern, Mastersizer 3000, United Kingdom). The surface morphology of the powder and the as-printed microstructure were analyzed using scanning electron microscope (SEM, FEI Quanta FEG 450). X-ray diffraction (XRD, MiniFlex 600) was conducted for phase analysis. Transmission electron microscopy (TEM, JEM-2010F, 200 kV) was used to detail the microstructure; the TEM samples were prepared using a focused ion beam (FIB, FEI Scios). High temperature differential scanning calorimeter (DSC, STA 8000) in a constant-rate heating mode (20 K/min) was used for thermal analysis. To check the amorphous status of the as-printed samples, three sample pieces from the upper, middle and lower locations of the Ø45 mm × 20 mm bulk sample was cut and analyzed. Nano-indentation (HYSIRON TI 950 Tribo Indenter) was used to evaluate the hardness; 12 sets of data from randomly-selected different areas of the polished sample (Ø12 mm × 6.5 mm, cut 5
from center of the as-printed BMG) were acquired and then averaged. The bulk mechanical properties of BMG were obtained by micropillar compression. The pillars (Ø1.5 µm × 3 µm) were prepared using FIB and tested by nano-indentation, which used a Flat Ended Conical (Nominal Flat Diameter of 10 µm) indenter whose Young's modulus is 1140 GPa and Poisson's ratio is 0.07, respectively.
3. Numerical simulation A finite element method (FEM) was used to analyze the full-scale temperature field and help understand the experimental results. It adopted a layer wise AM model using COMSOL Multiphysics 5.3a commercial software. The full-scale AM physical model was based on the governing behavior of conductive heat transfer in the track-by-track and layer-wise printing manner, see Complementary Materials and the corresponding Table S1 and Table S2.
4. Results Fig. 1(a) shows an SEM image of the spherical Fe55Cr25Mo16B2C2 BMG powder. Powder particle size analysis shows Dv (10) at 20.7 µm, Dv (50) at 34.7 µm, and Dv (90) at 65.8 µm. Fig. 1(b) shows a camera-snapshot image of the as-printed samples for exploring optimal SLM parameters. After systematic SLM experiments, a process map has been determined as the one shown in Fig. 1(c). Regions of ‘difficult to form’, ‘cracks’, ‘crystallization’ and ‘amorphous’ have been notified. The parameters for forming amorphous structure are pinpointed, where the laser powers are determined 6
as 100-300 W and scanning speeds are determined as 300-1000 mm/s. Such wide amorphous formation area suggests an excellent formability of the BMG by SLM. Furthermore, when the laser power is 100 W and the scanning rate is 300 mm/s (corresponding energy density = 105.8 J/mm3), the as-printed part is close to fully dense, reaching relative density of >99.0% and free of macroscopic defects like wrapping. It needs to mention that amorphous state of the as-printed samples is checked by both XRD and DSC. Fig. 1(d) provides a few typical examples, showing good parameters for forming amorphous state (e.g. 100 W and 400 mm/s) and the parameters that lead to more crystalline phases in the microstructure (e.g. 180 W and 600 mm/s). The BMG powder has been used as a reference as the fully amorphous state.
Based on the optimized SLM parameters, superlarge samples have been printed, Fig. 1(e). The largest ones are up to Ø45 mm × 20 mm. It is noted that their surface quality is good and macro delamination is not observable. In order to check the microstructure, XRD analysis is firstly conducted, confirming the bottom, the center and the top surface all staying in the amorphous states, Fig. 1(f). TEM is further employed and the typical results are shown in Fig. 1(g). Both the TEM bright field image and the selected area electron diffraction (SAED) pattern verify an amorphous structure, showing no phase contrast and only diffuse halo rings in Fig. 1(g) [2,17]. Thermal properties of the powder and the as-printed BMG sample have been subsequently compared using DSC. As shown in Fig. 1(h), it is measured that both 7
materials show the glass transition temperature Tg at ~833 K and the crystallization temperature Tx at ~ 883 K. Comparing exothermic enthalpy ∆H of the as-printed sample (= 67.73 J/g) with the amorphous powder (= 68.27 J/g), the corresponding ratio is ~99.21%, confirming a nearly full amorphous structure.
Furthermore, the mechanical properties of Fe-based BMG are evaluated. Nano-indentation curves are shown in Fig. 2(a), revealing an average nano-hardness of 14 GPa (Fig. 2b). The corresponding Vickers hardness is about 1260 HV. Such hardness is even higher than that of the Directed Metal Laser Sintering sample (~902 HV), supersonic plasma spraying coatings (1005 HV) or the atmospheric plasma spraying specimen (731±77 HV) of similar alloy compositions [16,18,19]. Micropillar compression has been further used to evaluate the fracture strength of as-printed BMG. Fig. 2(c) and (d) show the typical SEM images of the micropillar before and after compression. Fig. 2(e) shows the stress-strain curve. A few “pop-ins” are observable from the curve, implying that microfracture may have occurred during the loading procedure, which phenomenon is usually associated with brittle materials [20]. The yield strength of the as-printed BMG is ~4500 MPa. Furthermore, a micrograph is shown in Fig. 2(f), showing that microcracks may exist on some areas of the as-printed BMG. Such microscopic defects may have reduced the mechanical properties of the as-printed material [21].
Fig. 3(a) presents the FEM simulation results for the SLM processing, showing a 8
transient temperature profile for the molten pool and surrounding areas. The fiber laser for the SLM processing projects a near Gaussian TEM00 light onto the metal powder, showing its most intensity in the beam center and leading to a maximum temperature of ~ 2.34×103 K in the area directly beneath the beam. Considering that SLM is close to an infinite heat conduction, the cooling rate in the molten pool area (e.g. P1 in the figure) is ~1.38×106 K/s high. This is several orders larger than the critical cooling rate needed for forming amorphous structure (~ 549 K/s), guaranteeing an amorphous state [22]. Aside from the molten pool, in order to retain a bulk amorphous structure, temperatures and cooling rates of other areas in the as-printed sample are also critically important, such as those in the heat affected zone. Typical results for those areas are also shown in Fig. 3, when assuming their positions are ~150 µm (P2) and ~200 µm (P3), respectively, away from the beam center. The corresponding temperature-time variation is shown in Fig. 3(b). Critical temperature parameters, namely the Tg, Tx and Tm (=1423 K), of the BMG are shown in dotted lines in Fig. 3(b). It is noted that, although the temperature in the heat affected zone (P2) can be higher than Tx, the corresponding time window / lifetime of the high temperature period is rather short, i.e. ~0.8 ms. During this period of time, in theory the crystallization is possible to occur, but, in reality, an incubation period is required which needs ~1.87 ms [23]. Nucleation in this case cannot complete and amorphous structure remains due to the kinetic factor. Far end areas (e.g. P3) experience temperature rise that is lower than the Tg temperature, leading to no crystallization. The overall simulation results are therefore consistent with the XRD and TEM 9
characterizations in Fig. 1.
As shown in Fig. 4(a), development of the Fe-based BMGs from year 1995 to present is given in terms of the critical size obtained (in mm) and the corresponding time [8,24–32]. It is noted that, in the past 20 years (1995-2018), great progress has been made in terms of developing BMGs with larger critical sizes and better GFAs. The largest, fully amorphous Fe-based BMG, however, is still limited to ~ 16 mm by using conventional processing pathways, despite the two-decade intensive research efforts. In contrast, our current study presents that, by making good use of the unique characteristics of SLM, one can conveniently make amorphous Fe-based BMGs up to (Ø45 mm× 20 mm) large, achieving the best result so far.
Aside from making superlarge BMGs, another important advantage of SLM lies in its capability to make complex geometry part without the need of premade mould. This makes it appealing in manufacturing customized product such as the 36-teech gears as shown in Fig. 4(b). It demonstrates the capability of SLM to manufacture customer-designed, complex-geometry and large-sized BMG products.
5. Brief discussion To form superlarge BMGs is a challenging but rewarding task. Conventional methods such as copper mould casting can achieve cooling rate of 102-103 K/s and realize critical sizes of ~15 mm for Fe-based BMGs. Larger sized BMGs, however, require 10
novel technologies for providing sufficiently high cooling rate across the whole bulk sample. SLM is such technique. It delivers highly-localized, high-intensity and fast-scanned laser beam to melt metal powders, during which process the following criteria for retaining the amorphous structure are simultaneously satisfied: (a) A sufficiently high cooling rate during solidification to ensure an amorphous state to form, and (b) a sufficiently low-temperature environment to avoid subsequent crystallization, or a sufficiently short period of exposure time to temperatures higher than the corresponding Tg/Tx temperature. The current study confirms these by both experimental verification and computer simulation analysis. It implies that it is feasible to use SLM to fabricate large BMG products for the various industries.
6. Conclusion We report a record-large Fe-based BMG (Ø45 mm × 20 mm) that has been fabricated by SLM. The as-printed Fe55Cr25Mo16B2C2 BMG shows amorphous structure with evidences from XRD, DSC, TEM and FEM simulation. It presents high relative density (~ 99.0%), large nanohardness (14 GPa) and high yield strength (~4500 MPa). It is clarified that the lifetime of the molten pool is at the ms scale, corresponding to a rapid cooling rate of ~1.38×106 K/s. During printing, other locations of the sample experience either low temperatures (< Tg) or very short exposure time to high heat input, therefore avoiding crystallization due to thermodynamic and/or kinetic reasons and ensuring an amorphous structure across the whole as-printed sample. Demonstrative 36-teech gear part is present, implying that SLM may open up the 11
applications of BMGs by providing superlarge sized, customer-designed, quality parts.
Acknowledgments This work was supported by National Natural Science Foundation of China (Grant No.51771123) and the Shenzhen Peacock Innovation Project (Grant No. KQJSCX20170327151307811, KQJSCX20160226174209). Dr M. Yan appreciates the support by the Humboldt Research Fellowship for Experienced Researchers.
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References [1]
W. Klement, R. Willens, P. Duwez, © 1960 Nature Publishing Group, Nat. No. 4740. 187 (1960) 896–870. doi:10.1038/scientificamerican0268-74.
[2]
Y. Wang, J. Zhang, K. Wu, G. Liu, D. Kiener, J. Sun, Nanoindentation creep behavior of Cu–Zr metallic glass films, Mater. Res. Lett. 6 (2018) 22–28. doi:10.1080/21663831.2017.1383946.
[3]
W.H. Wang, R.J. Wang, F.Y. Li, D.Q. Zhao, M.X. Pan, Elastic constants and their pressure dependence of Zr41Ti14Cu12.5Ni9Be 22.5C1 bulk metallic glass, Appl. Phys. Lett. 74 (1999) 1803–1805. doi:10.1063/1.123091.
[4]
X.M. Huang, C.T. Chang, Z.Y. Chang, A. Inoue, J.Z. Jiang, Glass forming ability, mechanical and magnetic properties in Fe-W-Y-B alloys, Mater. Sci. Eng., A . 527 (2010) 1952–1956. doi:10.1016/j.msea.2009.11.042.
[5]
H. Li, S. Yi, Fabrication of bulk metallic glasses in the alloy system Fe-C-Si-B-P-Cr-Mo-Al using hot metal and industrial ferro-alloys, Mater. Sci. Eng. A. 448–451 (2007) 189–192. doi:10.1016/j.msea.2006.02.262.
[6]
Z.P. Lu, C.T. Liu, J.R. Thompson, W.D. Porter, Structural amorphous steels, Phys. Rev. Lett. 92 (2004) 1–4. doi:10.1103/PhysRevLett.92.245503.
[7]
V. Ponnambalam, S.J. Poon, G.J. Shiflet, Fe-Mn-Cr-Mo-(Y,Ln)-C-B (Ln = Lanthanides) bulk metallic glasses as formable amorphous steel alloys, J. Mater. Res. 19 (2004) 3046–3052. doi:10.1557/JMR.2004.0374.
[8]
J. Shen, Q. Chen, J. Sun, H. Fan, G. Wang, Exceptionally high glass-forming ability of an FeCoCrMoCBY alloy, Appl. Phys. Lett. 86 (2005) 1–3. 13
doi:10.1063/1.1897426. [9]
J.J. Yan, D.L. Zheng, H.X. Li, X. Jia, J.F. Sun, Y.L. Li, M. Qian, M. Yan, Selective laser melting of H13: microstructure and residual stress, J. Mater. Sci. 52 (2017) 12476–12485. doi:10.1007/s10853-017-1380-3.
[10] R. Laquai, B.R. Müller, G. Kasperovich, J. Haubrich, G. Requena, G. Bruno, X-ray refraction distinguishes unprocessed powder from empty pores in selective laser melting Ti-6Al-4V, Mater. Res. Lett. 6 (2018) 130–135. doi:10.1080/21663831.2017.1409288. [11] F. Audebert, R. Colaço, R. Vilar, H. Sirkin, Production of glassy metallic layers by laser surface treatment, Scr. Mater. 48 (2003) 281–286. doi:10.1016/S1359-6462(02)00382-2. [12] S. Katakam, J.Y. Hwang, S. Paital, R. Banerjee, H. Vora, N.B. Dahotre, In situ laser synthesis of Fe-based amorphous matrix composite coating on structural steel, Metall. Mater. Trans. A Phys. Metall. Mater. Sci. 43 (2012) 4957–4966. doi:10.1007/s11661-012-1312-4. [13] Y. Wang, G. Li, Z. Shi, M. Liu, X. Zhang, Y. Liu, Effects of graphite addition on the microstructure and properties of laser cladding Zr-Al-Ni-Cu amorphous coatings, J. Alloys Compd. 610 (2014) 713–717. doi:10.1016/j.jallcom.2014.05.009. [14] D. Ouyang, N. Li, W. Xing, J. Zhang, L. Liu, 3D printing of crack-free high strength Zr-based bulk metallic glass composite by selective laser melting, Intermetallics. 90 (2017) 128–134. doi:10.1016/j.intermet.2017.07.010. 14
[15] S. Pauly, L. Löber, R. Petters, M. Stoica, S. Scudino, U. Kühn, J. Eckert, Processing metallic glasses by selective laser melting, Mater. Today. 16 (2013) 37–41. doi:10.1016/j.mattod.2013.01.018. [16] Z. Mahbooba, L. Thorsson, M. Unosson, P. Skoglund, H. West, T. Horn, C. Rock, E. Vogli, O. Harrysson, Additive manufacturing of an iron-based bulk metallic glass larger than the critical casting thickness, Appl. Mater. Today. 11 (2018) 264–269. doi:10.1016/j.apmt.2018.02.011. [17] C. Zhang, L. Liu, K.C. Chan, Q. Chen, C.Y. Tang, Wear behavior of HVOF-sprayed Fe-based amorphous coatings, Intermetallics. 29 (2012) 80–85. doi:10.1016/j.intermet.2012.05.004. [18] Y. An, G. Hou, J. Chen, X. Zhao, G. Liu, H. Zhou, J. Chen, Microstructure and tribological properties of iron-based metallic glass coatings prepared by atmospheric plasma spraying, Vacuum. 107 (2014) 132–140. doi:10.1016/j.vacuum.2014.04.021. [19] Y. yang Zhou, G. zheng Ma, H. dou Wang, G.L. Li, S. ying Chen, H. jun Wang, Ming-Liu, Fabrication and characterization of supersonic plasma sprayed Fe-based amorphous metallic coatings, Mater. Des. 110 (2016) 332–339. doi:10.1016/j.matdes.2016.08.003. [20] C.A. Schuh, T.G. Nieh, A nanoindentation study of serrated flow in bulk metallic glasses, Acta Mater. 51 (2003) 87–99. doi:10.1016/S1359-6454(02)00303-8. [21] N. Li, J. Zhang, W. Xing, D. Ouyang, L. Liu, 3D printing of Fe-based bulk 15
metallic glass composites with combined high strength and fracture toughness, Mater. Des. 143 (2018) 285–296. doi:10.1016/j.matdes.2018.01.061. [22] Y. Huang, Y. Guo, H. Fan, J. Shen, Synthesis of Fe–Cr–Mo–C–B amorphous coating with high corrosion resistance, Mater. Lett. 89 (2012) 229–232. doi:10.1016/J.MATLET.2012.08.114. [23] D. Ouyang, W. Xing, N. Li, Y. Li, L. Liu, Structural evolutions in 3D-printed Fe-based metallic glass fabricated by selective laser melting, Addit. Manuf. 23 (2018) 246–252. doi:10.1016/j.addma.2018.08.020. [24] A. Inoue, Y. Shinohara, J.S. Gook, Thermal and Magnetic Properties of Bulk Fe-Based Glassy Alloys Prepared by Copper Mold Casting, Mater. Trans. JIM. 36 (1995) 1427–1433. doi:10.2320/matertrans1989.36.1427. [25] A. Inoue, T. Zhang, A. Takeuchi, Bulk amorphous alloys with high mechanical strength and good soft magnetic properties in Fe-TM-B (TM=IV-VIII group transition metal) system, Appl. Phys. Lett. 71 (1997) 464–466. doi:10.1063/1.119580. [26] B. Shen, H. Koshiba, H. Kimura, A. Inoue, High Strength and Good Soft Magnetic Properties of Bulk Glassy Fe–Mo–Ga–P–C–B Alloys with High Glass-Forming Ability, Mater. Trans. JIM. 41 (2000) 1478–1481. doi:10.2320/matertrans1989.41.1478. [27] V. Ponnambalam, S.J. Poon, G.J. Shiflet, V.M. Keppens, R. Taylor, G. Petculescu, Synthesis of iron-based bulk metallic glasses as nonferromagnetic 16
amorphous steel alloys, Appl. Phys. Lett. 83 (2003) 1131–1133. doi:10.1063/1.1599636. [28] V. Ponnambalam, S.J. Poon, G.J. Shiflet, Fe-based bulk metallic glasses with diameter thickness larger than one centimeter, J. Mater. Res. 19 (2004) 1320–1323. doi:10.1557/jmr.2004.0176. [29] K. Amiya, A. Inoue, Fe-(Cr,Mo)-(C,B)-Tm Bulk Metallic Glasses with High Strength and High Glass-Forming Ability, Mater. Trans. 47 (2006) 1615–1618. doi:10.2320/matertrans.47.1615. [30] A. Makino, T. Kubota, M. Makabe, C.T. Chang, A. Inoue, FeSiBP metallic glasses with high glass-forming ability and excellent magnetic properties, Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 148 (2008) 166–170. doi:10.1016/j.mseb.2007.09.010. [31] R. Nowosielski, R. Babilas, Glass-forming ability analysis of selected Fe-based bulk amorphous alloys, 42 (2010) 66–72. [32] P.H. Tsai, A.C. Xiao, J.B. Li, J.S.C. Jang, J.P. Chu, J.C. Huang, Prominent Fe-based bulk amorphous steel alloy with large supercooled liquid region and superior corrosion resistance, J. Alloys Compd. 586 (2014) 94–98. doi:10.1016/j.jallcom.2013.09.186.
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Figures caption Fig. 1 (a) SEM image of the amorphous alloy powder; figure inset shows the particle size distribution, (b) the as-printed samples for exploring optimal SLM parameters, (c) SLM processing map showing different characteristic areas. Different colors and different marks are used for highlighting the regions processed by varying laser powers and scanning speeds. Among these, the ‘amorphous’ region denotes that the as-printing microstructure are amorphous, ‘difficult to form’ means difficult to form a complete build, ‘crystallization’ refers to crystalized microstructure, ‘cracks’ refer to serious cracking, and ‘near full density’ means sample of >99% relative density, (d) the DSC curve of the original powder and three typical as-printed samples, (e) camera snapshot images of the 3D printed superlarge samples, (f) XRD pattern of the powder and superlarge sample slices of different locations, (g) TEM bright field image and the corresponding SAED pattern of the as-printed sample (sample from center location of the as-printed material), and (h) DSC analysis of the amorphous powder and the as-printed sample (sample from center location of the as-printed material).
Fig. 2 (a) Nano-indentation curves, and (b) nano-hardness of the as-printed sample (the test area was randomly selected), (c) and (d) show the typical SEM images of the micropillar before and after compression, (e) the stress-strain curve for the micro-compression sample, and (f) the cross-sectional microscopies of the BMG.
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Fig. 3 (a) Transient temperature field during the SLM processing determined by finite element simulation analysis, and (b) the temperature-time profiles of the molten pool (P1), heat affected zone (P2), and far site area (P3).
Fig. 4 (a) Development of Fe-based BMGs in term of their critical sizes, and (b) camera snapshot of an SLM-prepared 36-teech gear (tip circle diameter of 41.5 mm).
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