- Email: [email protected]
nano ductile-phases reinforced Fe-based bulk metallic glass matrix composite with large plasticity
Author’s Accepted Manuscript Micro/nano ductile-phases reinforced Fe-based bulk metallic glass matrix composite with large plasticity Shengfeng Guo, Chen Su www.elsevier.com/locate/msea
PII: DOI: Reference:
S0921-5093(17)31193-0 http://dx.doi.org/10.1016/j.msea.2017.09.036 MSA35503
To appear in: Materials Science & Engineering A Received date: 16 July 2017 Revised date: 9 September 2017 Accepted date: 9 September 2017 Cite this article as: Shengfeng Guo and Chen Su, Micro/nano ductile-phases reinforced Fe-based bulk metallic glass matrix composite with large plasticity, Materials Science & Engineering A, http://dx.doi.org/10.1016/j.msea.2017.09.036 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.
Micro/nano ductile-phases reinforced Fe-based bulk metallic glass matrix composite with large plasticity Shengfeng Guo, Chen Su Faculty of Materials and Energy, Southwest University, Chongqing 400715, China
Abstract Fe-based bulk metallic glasses (BMGs) often show an extremely poor plastic deformation ability at room temperature, which seriously restricted their wide application. In this work, a series of in-situ (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) BMG matrix composites were successfully developed by low purity industrial raw materials using copper mold casting. An (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 BMG matrix composite reinforced by the dual heterogeneous structure with micro/nano α-Fe exhibits the highest ever reported compressive plasticity of ~6.6% during the testing rod with a diameter of 1.5 mm. The origin of a large plasticity of this Fe-based BMG composite has been discussed according to the initiation of the shear bands and the instability of the shear banding.
Keywords: Fe-based bulk metallic glass; composite; plasticity
Corresponding author. E-mail address: [email protected] (S.F. Guo)
1. Introduction Bulk metallic glasses (BMGs) are a novel class of revolutionizing metallic materials, which characterized by ultrahigh strength, large elasticity, and excellent corrosion resistance compared with their crystalline counterparts. Therefore, BMGs materials offer a great potential for a wide variety of applications [1-3]. Unfortunately, the mass commercialization and industrialization of these monolithic BMGs still remain unsolved due to some limitations, such as the high materials fabrication cost and the notorious room-temperature plasticity [4]. Among all of the BMG alloy systems, Fe-based BMGs show more attractive potentials due to the combination of ultrahigh strength and relatively low material cost [5-8]. However, most of the Fe-based BMGs currently have a very poor plasticity at room temperature, which critically hinders their widespread use and mass production [9-12]. Recently, it has been demonstrated that in-situ or ex-situ formation of BMG matrix composite through introduction of the second dendrites or particles can significantly enhance the room-temperature plasticity of these BMGs [13]. For example, in 2000, Hays et al. [14] reported an in-situ formation of ductile dendrite phase with bcc structure reinforced in a Zr-based BMG matrix, which resulted a large increase in the compressive plasticity, impact resistance, and toughness. After that, some other systems like Ti-based [15], Cu-based [16] and Mg-based [17] BMGs can also use this route to enhance the room-temperature plasticity. Although the development of Fe-based BMG matrix composite would be an interesting research direction [12], the same things were not going as well as we expected in Fe-based BMGs. Until in 2006, Shen et al. [18] reported a Fe35.91Co35.91B19.15Si4.79Nb3.99Cu0.25 BMG matrix composite contains the soft α-(Fe, Co) combining with the brittle fcc-(Fe, Co)23B6 microcrystalline grains, and exhibits a plasticity of only 0.6% for using the specimen rod of 2 mm in diameter. In 2010, Guo et al. [19] successfully developed the micrometer-sized α-Fe dendrites reinforced in FePC-based BMGs, which shows over 30% room-temperature plasticity under the compression rod with a diameter of 1mm. In 2010, Li et al. [20] reported with a small addition of Cu in Fe-based BMG resulted
a large number of α-Fe nanocrystals embedded in a glassy matrix, which shows 3.1% room-temperature plasticity during the compression rod with a diameter of 1.5 mm. However, the detailed formation rule for the Fe-based BMG matrix composite was still not fully understood. There is no doubt that the development of large scale Fe-based BMG matrix composite with good plastic deformation ability have a great potential for a deep-understanding the formation mechanism and the room temperature deformation behaviors of Fe-based BMG composite. In this work, we aim to develop a new in-situ formed Fe-based BMG matrix composite with different length-scaled heterogeneity, which contains both micrometer sized and nanometer sized phases, and decode the deformation behavior of the multi-scale heterogeneous structure reinforced Fe-based BMG matrix composites. The Fe77Mo5P9C7.5B1.5 BMG matrix composite was selected as the initial alloy due to the micrometer sized α-Fe dendrites formed on the BMG matrix [19]. By micro-alloying with Cu element, we have successfully prepared a series of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7 and 1 at.%) BMGs matrix composites with a different length scale of heterogeneous structures by using low purity industrial raw materials and conventional copper mold casting, which markedly reduced the materials and fabrication cost. The room temperature deformation behaviors of these novel Fe-based BMG matrix composites were also discussed. 2 Experiment methods The alloy ingots of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) were prepared by arc-melting the mixtures of low purity Fe (99.5 wt.%), Mo (99.9 wt.%), C (99.9 wt.%), B (99.5 wt.%), Cu (99.99 wt.%) and industrial Fe-P alloy (72.6 wt.% Fe, 25.3 wt.% P and other impurities in remainder) under a Ti-gettered argon atmosphere. The specimen rod with a diameter of 1.5 mm was produced by copper mold suck-casting with water cooling. The microstructure of the as-cast alloys was identified by X-ray diffraction (XRD, SHIMADZU XRD-6100) with Cu-Kɑ radiation and a scanning electron microscope (SEM, JSM-6610), respectively. For further
observation in the transmission electron microscopy (TEM), the different structure region of the sample was fabricated by focused ion beam (FIB) using a FEI Helios Nanolab 650 Dualbeam FIB with a Ga ion source. A very thin layer of platinum was deposited over the desired region of the interest to avoid excessive Ga ion damage. A 30 kV beam operating at 2.3 nA was used to excavate the sample from both sides of the region to a depth of 5 μm. And then, the sample was thinned further using a final milling beam current of 80 pA. The sample was lifted out in-situ by welding to the micromanipulator and was subsequently moved to a TEM sample holder. Further characterization in a JEOL 3011 was performed for higher magnification. The thermal properties was examined by a differential scanning calorimetry (DSC, Perkin-Elmer 8000) at a heating rate of 20 K/min under Ar atmosphere. The room-temperature compression rod with a diameter of 1.5 mm and a length of ~ 3 mm were cut from the as-cast rods, and the two ends were polished carefully to ensure parallelism. Uniaxial compression was performed on a testing machine (Reger, RGM-4300) under a strain rate of 1×10-4 s-1. At least five specimens were tested for each composition to ensure the reproducibility of the results. The fractured morphologies were also examined with a SEM. 3 Results Fig. 1 shows the XRD patterns of the as-cast (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloy rods with a diameter of 1.5 mm. All the specimen exhibit a diffraction peaks associated with the crystal structure superimposed on the broad diffraction halo from the amorphous phase. By comparing with the standard PDF card, the crystalline of the alloys for x=0, 0.1, 0.3, 0.5 and 0.7 at.% were determined to be a bcc α-Fe phase, which were coincident with our pervious reported [19]. However, the Fe3P phase and Fe2B phase were precipitated simultaneously beside of the α-Fe phase when addition of 1 at.% Cu on the present alloy. Therefore, it can be concluded that a little of Cu addition would not dramatically destroy the glass forming ability (GFA) of this Fe-based BMG, resulting the main precipitation of the
α-Fe phase on the amorphous matrix. However, the Fe3P phase, Fe2B phase, and α-Fe phase were precipitated at same time from the Fe-based BMG with an excessive addition of Cu, implying that a decrease in the GFA of this Fe-based BMG matrix composite. Fig. 2 displays the DSC curves of the as-cast (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloy. Except for the x=1 at.% alloy, the Fe-based BMG matrix composites reveal a distinct glass transition followed by a supercooled liquid region before the multi-step crystallization. Combination with the XRD results, it can be confirmed that the alloy matrix were indeed mainly amorphous phase even the precipitation of the α-Fe phase on the Fe-based BMG matrix. However, for the alloy with 1 at.% Cu, it shows an approximate straight line without distinctly exothermic peaks, implying that there was no evidence for glass transition and glassy phase remain in this alloy. The glass transition temperature Tg, the onset crystallization temperature Tx, the supercooled liquid region ∆Tx, and the enthalpy of crystallization ∆H are summarized in Table 1. It can be found that with the increase of Cu additions, the ∆H decrease monotonously, conforming that the volume fraction of the amorphous phase was gradually decreased as the increase of Cu content. To further investigate the morphologies of precipitation, the SEM images of the cross-sectional of the samples with different Cu were shown in Fig. 3. It can be seen that the volume fraction of the micrometer-sized dendrites and the dendrite size increased with Cu addition. The volume fraction of the dendrites span the range from 40% to 100%. These percentages were obtained by analyzing the contrast from SEM images using computer software, and also independently verified by analyzing the enthalpy of crystallization ∆H in their DSC scans relative to the ∆H from a fully Fe-based BMG matrix [19]. According to the XRD results, these micro-sized dendrites were mainly α-Fe phase except for the alloy with 1 at.% Cu, which was hardly to find the amorphous matrix. The Fe-based BMG matrix composite with only 1% Cu addition resulted the precipitation of fully intermetallic phases, implying that the relatively poor GFA of the current FePC-based BMGs [21]. Fig. 4 shows the typical engineering stress–strain curves of the as-cast
(Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloys rods with a diameter of 1.5mm. The original Fe77Mo5P9C7.5B1.5 BMG matrix exhibits a good plastic deformation ability even by using the low purity Fe for fabrication. The compressive plasticity was about 4% for the testing rod with a diameter of 1.5mm. Interestingly, with a little of Cu doping, the (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy shows a high yield strength of ~3100 MPa with a plasticity of ~6.6%. To our best knowledge, the present Fe-based BMG matrix composite exhibits the highest ever reported compressive plasticity when the specimen rod under 1.5 mm in diameter. However, with further increasing of Cu, the deformation ability of the Fe-based BMG matrix composite was gradually decreased, especially for the Cu contents equal or more than 0.7 at.%, which show an ideally brittle behavior, i.e. a catastrophic failure immediately after elastic deformation without discernible plasticity. The yield strength σy, defined by the deviation from the linear relation in the stress-strain cure, σmax and plastic strain ɛ p of the alloys were also summarized and listed in Table 1. Fig. 5 exhibits the fracture morphologies of the (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy with the best plasticity in current work. It can be seen that the compression sample failed into two pieces of big fragments (see Fig. 5a), exhibiting a characteristic shear failure at an inclined angle to the compression axis, which failed via localized plastic shear flow and very similar to the ductile Zr-based BMGs [22]. The failure mode of this Fe-based BMG matrix composite shows no "explosive" fracture that often occur in most of the brittle Fe-based BMGs [23], demonstrating that the plastic deformation ability of this composite is much better than most of the brittle Fe-based BMGs. Furthermore, a great number of secondary shear bands parallel to the main shear band and multiple shear bands were shown on the cylindrical surface (see Fig. 5b and Fig. 5c, respectively). These shear bands were significantly deflected and bifurcated several times, indicating that the main shear band encountered many obstacles at the same time and also induced a number of shear bands formation, which can effectively suppressed the shear band instability during plastic flow. Therefore, the main shear band was not easy to develop into microcracks and resulting an enhanced of the plastic deformation ability for the Fe-based BMG matrix composite. The fractured
surface of the Fe-based BMG matrix composite (see Fig. 5d and Fig. 5e) illustrates both a well-developed vein pattern as indicated in region I and a relatively smooth area as indicated in region II (see Fig. 5f). Compared to the monolithic Fe-based BMGs [24], the typical shear vein patterns shown in region I of the Fe-based BMG matrix composite are relatively rough, indicating that the dendrite phase effectively impeded the immediate shear-off and failure during shear band propagation. The formation of region II was probably caused by the whole slip or movement of a dendrite phase when the glassy matrix softened due to the adiabatic heating during fracture moment [19]. 4 Discussion From the microstructure perspective to further understand the effect of Cu on the deformation behavior of Fe-based BMG matrix composites, we focus on the TEM study of the microstructure with Cu=0, 0.1, 0.5 at.% alloys. For the Cu-free Fe77Mo5P9C7.5B1.5 alloy (see Fig. 6a), it shows only two distinct regions, i.e. the micrometer-sized dendrites and the alloy matrix. Fig. 6b and Fig. 6c show the high resolution TEM images of the two regions, demonstrating that the micrometer-sized dendrites were α-Fe phases and the matrix was typically amorphous phases within the TEM resolution. The microstructure characteristics of the current Fe-based matrix composite was consistent with our previous report [22] even using low purity raw materials. Because of the strong interaction between the micrometer-sized α-Fe dendrites and the shear bands, it can hinder the rapid instability of the main shear bands and result a good compressive plastic strain of ~ 4% at the specimen rod of 1.5 mm in diameter. For a little of Cu doping, the (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 BMG matrix composite also exhibits two different regions including the micrometer-sized α-Fe dendrites and the amorphous matrix under TEM observation (see Fig. 7a). Interestingly, when the glassy matrix was further amplified, some nanocrystals from 1nm to 10 nm were clearly embedded in the glassy matrix (see Fig. 7b and Fig. 7c). The local FFT
analysis of these nanosized particles was performed and the patterns can be indexed as α-Fe (see the inset of Fig. 7b). The precipitation of nano-scaled α-Fe was probably resulted from the positively mixing enthalpy between Fe and Cu (13 kJ/mol). Therefore, a repulsive interaction should exist between Fe and Cu atoms, which contributed
to
the
nanocrystals
α-Fe
formation
[25].
The
present
(Fe77Mo5P9C7.5B1.5)99.9Cu0.1 BMG matrix composite exhibited two different scale of heterogeneous
structures;
the
micrometer-sized
α-Fe
dendrites
and
the
nanometer-sized α-Fe particles. The nanocrystal particles would probably act as the initiation sites for the multiple shear band initiation on the glassy matrix under compression, and the microscale α-Fe dendrites could strong interact with the shear bands during the shear bands propagation, which resulting the shear bands deflecting and branching. Therefore, the Fe-based BMG matrix composite with multi-scaled heterogeneous structures could effectively hinder the rapid instability of the shear banding and form a great number of the branching shear bands, leading to a distinctly enhanced on the room-temperature plasticity. However, the size of the nano-particles would increase with Cu addition as shown in the TEM images for x=0.5 at.% alloy in Fig. 8a. The size of α-Fe nanocrystal was around 20 nm (see Fig. 8b and Fig. 8c), which is above the shear bandwidth (10 nm) [26]. In contrast, large particles with a size above the shear bandwidth cannot have some effect on the shear band propagation. The shear band probably shear off when they encounter these nanocrystals, rather than block or circle, resulting a decrease of the plastic strain. This demonstrated that the room-temperature deformation ability of Fe-based BMG matrix composite was strongly related to the critical length scale of the microstructural heterogeneity [27], i.e., an appropriate of nano-scale and micro-scale α-Fe phases, leading to an enhanced plasticity by a combined effect of initiation and stability of shear bands. In additions, unlike the monolithic BMGs, the current Fe-based BMG matrix composites show the work hardening deformation behavior under room temperature, which may be due to a large amount of α-Fe is involved in plastic deformation. These results will open the way for designing of high performance Fe-based BMG matrix composite with multi-scaled
heterogeneous structures. 5 Conclusion In summary, in-situ formed (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) BMG matrix composites reinforced with microscale and nanoscale α-Fe phases have been successfully developed by copper mold casting using low purity raw materials. The (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 composite exhibits a record plasticity of 6.6% under the compression rod of 1.5 mm in diameter, together with high fracture strength of 3.1 GPa. The origin of the significant enhancement in plasticity is due to the combining effect from the initiation of shear bands and the stability of shear banding. The room-temperature deformation ability of Fe-based BMG matrix composite is strongly related to the critical length scale of the microstructural heterogeneity, i.e., nano-scale and micro-scale α-Fe phases. Our results will open the way for designing of high performance Fe-based BMG matrix composite using low purity raw materials for the engineering industry. Acknowledgements The authors would like to thank Dr. Feifei Zhang from University of Michigan for providing TEM assistance. This work was financially supported by the National Natural Science Foundation of China (Nos. 51671162 and 51301142), the Fundamental Research Funds for the Central Universities (No. XDJK2017B054) and Chongqing Research Program of Basic Research and Frontier Technology (No. cstc2015jcyjBX0107). References [1] W.L. Johnson, MRS Bull 32 (1999) 42-56. [2] A. Inoue, Acta Mater. 48 (2000) 279-306. [3] W.H. Wang, C. Dong, C.H. Shek, Mater. Sci. Eng. R. 44 (2004) 45-89. [4] W.L. Johnson. Nat. Mater. 14 (2015) 553-555.
[5] A. Inoue, Y. Shinohara, J.S. Gook, Mater. Trans. 36 (1995) 1427-1433. [6] A. Inoue, B.L. Shen, A.R. Yavari, A.L. Greer, J. Mater. Res. 18 (2003) 1487-1492. [7] C. Su, Y. Chen, P. Yu, M. Song , W. Chen, S.F. Guo, J. Alloys. Compd. 663 (2016) 867-871. [8] S.F. Guo, L. Liu, X. Lin, J. Alloys. Compd. 478 (2009) 226-228. [9] Z.P. Lu, C.T. Liu, J.R. Thompson, W.D. Porter, Phys. Rev. Lett. 92 (2004) 245503. [10] V. Ponnambalam, S.J. Poon, J. Mater. Res. 19 (2004) 1320-1323. [11] M. Stoica, J. Eckerta, S. Roth, Z.F. Zhang, L. Schultz, W.H. Wang, Intermetallics. 13 (2005) 764-769. [12] X.J. Gu, S.J. Poon, J. Mater. Res. 22 (2007) 344-351. [13] J.W. Qiao, H.L. Jia, P.K. Liaw, Mater. Sci. Eng. R. 100 (2016) 1-69. [14] C.C. Hays, C.P. Kim, W.L. Johnson, Phys. Rev. Lett. 84 (2000) 2091-2094. [15] D.C. Hofmann, J.Y. Suh, A. Wiest, M.L. Lind, M.D. Demetriou, W.L. Johnson, Proc. Natl. Acad. Sci. USA 105 (2008) 20136-20140. [16] Y.C. Kim, D.H. Kim, J.C. Lee, Mater. Trans. 44 (2003) 2224-2227. [17] H. Ma, J. Xu, E. Ma, Appl. Phys. Lett. 83 (2003) 2793-2795. [18] B.L. Shen, H. Men, A. Inoue, Appl. Phys. Lett. 89 (2006) 101915. [19] S.F. Guo, L. Liu, N. Li, Y. Li, Scripta Mater. 62 (2010) 329-332. [20] X. Li, H. Kato, K. Yubuta, A. Makino, A. Inoue, Mater. Sci. Eng. A. 527 (2010) 2598-2602. [21] S.F. Guo, J.L. Qiu, P. Yu, S.H. Xie, W. Chen, Appl. Phys. Lett. 105 (2014) 161901 [22] Y.H. Liu, G. Wang, R.J. Wang, D.Q. Zhao, M.X. Pan, W.H. Wang, Science 315 (2007) 1385-1388. [23] J.X. Zhao, R.T. Qu, F.F. Wu, Z.F. Zhang, B.L. Shen, M. Stoica, J. Eckert, J. Appl. Phys. 105 (2009) 103519 [24] S.F. Guo, N. Li, C. Zhang, L. Liu, Journal of Alloys and Compounds 504 (2010) 78 [25] A. Makino, X. Li, K. Yubuta, C.T. Chang, T. Kubota, A. Inoue, Scripta Mater. 60 (2009) 277-280 [26] J. Li, F. Spaepen, T.C. Hufnagel, Philos. Mag. A 82 (2002) 2623-2630. [27] J.M. Park, D.H. Kim, M. Stoica, N. Mattern, R. Li, J. Eckert. J. Mater. Res. 26 (2011) 2080-2086.
Figure captions
Fig. 1 The XRD patterns of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7 and 1 at.%) alloy.
Fig. 2 The DSC curves of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7 and 1 at.%) alloys at a heat rate of 20 K/min, respectively.
Fig.
3
The
SEM
backscattered
electron
images
of
(Fe77Mo5P9C7.5B1.5)100-xCux alloys with different Cu. (a) x=0; (b) x=0.1; (c) x=0.3; (d) x=0.5; (e) x=0.7; (f) x=1.
Fig. 4 The strain-stress curves of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloy rod with a diameter of 1.5 mm under room-temperature compression.
Fig. 5 The SEM images of fractured (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy. Fig. 6 The TEM images of Fe77Mo5P9C7.5B1.5 alloy (a); the corresponding high-resolution TEM images of dendrites (b) and the matrix (c), respectively.
Fig. 7 The TEM images of (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy (a), and the high-resolution TEM images showing the nanocrystal size from 1 nm (b) to 10 nm (c).
Fig. 8 The TEM images of (Fe77Mo5P9C7.5B1.5)99.5Cu0.5 alloy.
Table 1 The thermal characteristics and mechanical properties of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloys. Alloy
Tg/K
Tx/K
ΔTx/K
ΔH(J/g)
σy (MPa)
σmax (MPa)
ɛ p (%)
x=0
729
790
61
-34.4
2300
2900
3.9
x=0.1
721
778
57
-28.3
2450
3100
6.6
x=0.3
726
772
46
-27.1
2270
2900
3.5
x=0.5
726
773
47
-16.4
2170
2800
0.9
x=0.7
714
777
63
-9.8
2500
2500
-
x=1
-
-
-
-
2100
2100
-
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
PII: DOI: Reference:
S0921-5093(17)31193-0 http://dx.doi.org/10.1016/j.msea.2017.09.036 MSA35503
To appear in: Materials Science & Engineering A Received date: 16 July 2017 Revised date: 9 September 2017 Accepted date: 9 September 2017 Cite this article as: Shengfeng Guo and Chen Su, Micro/nano ductile-phases reinforced Fe-based bulk metallic glass matrix composite with large plasticity, Materials Science & Engineering A, http://dx.doi.org/10.1016/j.msea.2017.09.036 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. 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.
Micro/nano ductile-phases reinforced Fe-based bulk metallic glass matrix composite with large plasticity Shengfeng Guo, Chen Su Faculty of Materials and Energy, Southwest University, Chongqing 400715, China
Abstract Fe-based bulk metallic glasses (BMGs) often show an extremely poor plastic deformation ability at room temperature, which seriously restricted their wide application. In this work, a series of in-situ (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) BMG matrix composites were successfully developed by low purity industrial raw materials using copper mold casting. An (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 BMG matrix composite reinforced by the dual heterogeneous structure with micro/nano α-Fe exhibits the highest ever reported compressive plasticity of ~6.6% during the testing rod with a diameter of 1.5 mm. The origin of a large plasticity of this Fe-based BMG composite has been discussed according to the initiation of the shear bands and the instability of the shear banding.
Keywords: Fe-based bulk metallic glass; composite; plasticity
Corresponding author. E-mail address: [email protected] (S.F. Guo)
1. Introduction Bulk metallic glasses (BMGs) are a novel class of revolutionizing metallic materials, which characterized by ultrahigh strength, large elasticity, and excellent corrosion resistance compared with their crystalline counterparts. Therefore, BMGs materials offer a great potential for a wide variety of applications [1-3]. Unfortunately, the mass commercialization and industrialization of these monolithic BMGs still remain unsolved due to some limitations, such as the high materials fabrication cost and the notorious room-temperature plasticity [4]. Among all of the BMG alloy systems, Fe-based BMGs show more attractive potentials due to the combination of ultrahigh strength and relatively low material cost [5-8]. However, most of the Fe-based BMGs currently have a very poor plasticity at room temperature, which critically hinders their widespread use and mass production [9-12]. Recently, it has been demonstrated that in-situ or ex-situ formation of BMG matrix composite through introduction of the second dendrites or particles can significantly enhance the room-temperature plasticity of these BMGs [13]. For example, in 2000, Hays et al. [14] reported an in-situ formation of ductile dendrite phase with bcc structure reinforced in a Zr-based BMG matrix, which resulted a large increase in the compressive plasticity, impact resistance, and toughness. After that, some other systems like Ti-based [15], Cu-based [16] and Mg-based [17] BMGs can also use this route to enhance the room-temperature plasticity. Although the development of Fe-based BMG matrix composite would be an interesting research direction [12], the same things were not going as well as we expected in Fe-based BMGs. Until in 2006, Shen et al. [18] reported a Fe35.91Co35.91B19.15Si4.79Nb3.99Cu0.25 BMG matrix composite contains the soft α-(Fe, Co) combining with the brittle fcc-(Fe, Co)23B6 microcrystalline grains, and exhibits a plasticity of only 0.6% for using the specimen rod of 2 mm in diameter. In 2010, Guo et al. [19] successfully developed the micrometer-sized α-Fe dendrites reinforced in FePC-based BMGs, which shows over 30% room-temperature plasticity under the compression rod with a diameter of 1mm. In 2010, Li et al. [20] reported with a small addition of Cu in Fe-based BMG resulted
a large number of α-Fe nanocrystals embedded in a glassy matrix, which shows 3.1% room-temperature plasticity during the compression rod with a diameter of 1.5 mm. However, the detailed formation rule for the Fe-based BMG matrix composite was still not fully understood. There is no doubt that the development of large scale Fe-based BMG matrix composite with good plastic deformation ability have a great potential for a deep-understanding the formation mechanism and the room temperature deformation behaviors of Fe-based BMG composite. In this work, we aim to develop a new in-situ formed Fe-based BMG matrix composite with different length-scaled heterogeneity, which contains both micrometer sized and nanometer sized phases, and decode the deformation behavior of the multi-scale heterogeneous structure reinforced Fe-based BMG matrix composites. The Fe77Mo5P9C7.5B1.5 BMG matrix composite was selected as the initial alloy due to the micrometer sized α-Fe dendrites formed on the BMG matrix [19]. By micro-alloying with Cu element, we have successfully prepared a series of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7 and 1 at.%) BMGs matrix composites with a different length scale of heterogeneous structures by using low purity industrial raw materials and conventional copper mold casting, which markedly reduced the materials and fabrication cost. The room temperature deformation behaviors of these novel Fe-based BMG matrix composites were also discussed. 2 Experiment methods The alloy ingots of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) were prepared by arc-melting the mixtures of low purity Fe (99.5 wt.%), Mo (99.9 wt.%), C (99.9 wt.%), B (99.5 wt.%), Cu (99.99 wt.%) and industrial Fe-P alloy (72.6 wt.% Fe, 25.3 wt.% P and other impurities in remainder) under a Ti-gettered argon atmosphere. The specimen rod with a diameter of 1.5 mm was produced by copper mold suck-casting with water cooling. The microstructure of the as-cast alloys was identified by X-ray diffraction (XRD, SHIMADZU XRD-6100) with Cu-Kɑ radiation and a scanning electron microscope (SEM, JSM-6610), respectively. For further
observation in the transmission electron microscopy (TEM), the different structure region of the sample was fabricated by focused ion beam (FIB) using a FEI Helios Nanolab 650 Dualbeam FIB with a Ga ion source. A very thin layer of platinum was deposited over the desired region of the interest to avoid excessive Ga ion damage. A 30 kV beam operating at 2.3 nA was used to excavate the sample from both sides of the region to a depth of 5 μm. And then, the sample was thinned further using a final milling beam current of 80 pA. The sample was lifted out in-situ by welding to the micromanipulator and was subsequently moved to a TEM sample holder. Further characterization in a JEOL 3011 was performed for higher magnification. The thermal properties was examined by a differential scanning calorimetry (DSC, Perkin-Elmer 8000) at a heating rate of 20 K/min under Ar atmosphere. The room-temperature compression rod with a diameter of 1.5 mm and a length of ~ 3 mm were cut from the as-cast rods, and the two ends were polished carefully to ensure parallelism. Uniaxial compression was performed on a testing machine (Reger, RGM-4300) under a strain rate of 1×10-4 s-1. At least five specimens were tested for each composition to ensure the reproducibility of the results. The fractured morphologies were also examined with a SEM. 3 Results Fig. 1 shows the XRD patterns of the as-cast (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloy rods with a diameter of 1.5 mm. All the specimen exhibit a diffraction peaks associated with the crystal structure superimposed on the broad diffraction halo from the amorphous phase. By comparing with the standard PDF card, the crystalline of the alloys for x=0, 0.1, 0.3, 0.5 and 0.7 at.% were determined to be a bcc α-Fe phase, which were coincident with our pervious reported [19]. However, the Fe3P phase and Fe2B phase were precipitated simultaneously beside of the α-Fe phase when addition of 1 at.% Cu on the present alloy. Therefore, it can be concluded that a little of Cu addition would not dramatically destroy the glass forming ability (GFA) of this Fe-based BMG, resulting the main precipitation of the
α-Fe phase on the amorphous matrix. However, the Fe3P phase, Fe2B phase, and α-Fe phase were precipitated at same time from the Fe-based BMG with an excessive addition of Cu, implying that a decrease in the GFA of this Fe-based BMG matrix composite. Fig. 2 displays the DSC curves of the as-cast (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloy. Except for the x=1 at.% alloy, the Fe-based BMG matrix composites reveal a distinct glass transition followed by a supercooled liquid region before the multi-step crystallization. Combination with the XRD results, it can be confirmed that the alloy matrix were indeed mainly amorphous phase even the precipitation of the α-Fe phase on the Fe-based BMG matrix. However, for the alloy with 1 at.% Cu, it shows an approximate straight line without distinctly exothermic peaks, implying that there was no evidence for glass transition and glassy phase remain in this alloy. The glass transition temperature Tg, the onset crystallization temperature Tx, the supercooled liquid region ∆Tx, and the enthalpy of crystallization ∆H are summarized in Table 1. It can be found that with the increase of Cu additions, the ∆H decrease monotonously, conforming that the volume fraction of the amorphous phase was gradually decreased as the increase of Cu content. To further investigate the morphologies of precipitation, the SEM images of the cross-sectional of the samples with different Cu were shown in Fig. 3. It can be seen that the volume fraction of the micrometer-sized dendrites and the dendrite size increased with Cu addition. The volume fraction of the dendrites span the range from 40% to 100%. These percentages were obtained by analyzing the contrast from SEM images using computer software, and also independently verified by analyzing the enthalpy of crystallization ∆H in their DSC scans relative to the ∆H from a fully Fe-based BMG matrix [19]. According to the XRD results, these micro-sized dendrites were mainly α-Fe phase except for the alloy with 1 at.% Cu, which was hardly to find the amorphous matrix. The Fe-based BMG matrix composite with only 1% Cu addition resulted the precipitation of fully intermetallic phases, implying that the relatively poor GFA of the current FePC-based BMGs [21]. Fig. 4 shows the typical engineering stress–strain curves of the as-cast
(Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloys rods with a diameter of 1.5mm. The original Fe77Mo5P9C7.5B1.5 BMG matrix exhibits a good plastic deformation ability even by using the low purity Fe for fabrication. The compressive plasticity was about 4% for the testing rod with a diameter of 1.5mm. Interestingly, with a little of Cu doping, the (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy shows a high yield strength of ~3100 MPa with a plasticity of ~6.6%. To our best knowledge, the present Fe-based BMG matrix composite exhibits the highest ever reported compressive plasticity when the specimen rod under 1.5 mm in diameter. However, with further increasing of Cu, the deformation ability of the Fe-based BMG matrix composite was gradually decreased, especially for the Cu contents equal or more than 0.7 at.%, which show an ideally brittle behavior, i.e. a catastrophic failure immediately after elastic deformation without discernible plasticity. The yield strength σy, defined by the deviation from the linear relation in the stress-strain cure, σmax and plastic strain ɛ p of the alloys were also summarized and listed in Table 1. Fig. 5 exhibits the fracture morphologies of the (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy with the best plasticity in current work. It can be seen that the compression sample failed into two pieces of big fragments (see Fig. 5a), exhibiting a characteristic shear failure at an inclined angle to the compression axis, which failed via localized plastic shear flow and very similar to the ductile Zr-based BMGs [22]. The failure mode of this Fe-based BMG matrix composite shows no "explosive" fracture that often occur in most of the brittle Fe-based BMGs [23], demonstrating that the plastic deformation ability of this composite is much better than most of the brittle Fe-based BMGs. Furthermore, a great number of secondary shear bands parallel to the main shear band and multiple shear bands were shown on the cylindrical surface (see Fig. 5b and Fig. 5c, respectively). These shear bands were significantly deflected and bifurcated several times, indicating that the main shear band encountered many obstacles at the same time and also induced a number of shear bands formation, which can effectively suppressed the shear band instability during plastic flow. Therefore, the main shear band was not easy to develop into microcracks and resulting an enhanced of the plastic deformation ability for the Fe-based BMG matrix composite. The fractured
surface of the Fe-based BMG matrix composite (see Fig. 5d and Fig. 5e) illustrates both a well-developed vein pattern as indicated in region I and a relatively smooth area as indicated in region II (see Fig. 5f). Compared to the monolithic Fe-based BMGs [24], the typical shear vein patterns shown in region I of the Fe-based BMG matrix composite are relatively rough, indicating that the dendrite phase effectively impeded the immediate shear-off and failure during shear band propagation. The formation of region II was probably caused by the whole slip or movement of a dendrite phase when the glassy matrix softened due to the adiabatic heating during fracture moment [19]. 4 Discussion From the microstructure perspective to further understand the effect of Cu on the deformation behavior of Fe-based BMG matrix composites, we focus on the TEM study of the microstructure with Cu=0, 0.1, 0.5 at.% alloys. For the Cu-free Fe77Mo5P9C7.5B1.5 alloy (see Fig. 6a), it shows only two distinct regions, i.e. the micrometer-sized dendrites and the alloy matrix. Fig. 6b and Fig. 6c show the high resolution TEM images of the two regions, demonstrating that the micrometer-sized dendrites were α-Fe phases and the matrix was typically amorphous phases within the TEM resolution. The microstructure characteristics of the current Fe-based matrix composite was consistent with our previous report [22] even using low purity raw materials. Because of the strong interaction between the micrometer-sized α-Fe dendrites and the shear bands, it can hinder the rapid instability of the main shear bands and result a good compressive plastic strain of ~ 4% at the specimen rod of 1.5 mm in diameter. For a little of Cu doping, the (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 BMG matrix composite also exhibits two different regions including the micrometer-sized α-Fe dendrites and the amorphous matrix under TEM observation (see Fig. 7a). Interestingly, when the glassy matrix was further amplified, some nanocrystals from 1nm to 10 nm were clearly embedded in the glassy matrix (see Fig. 7b and Fig. 7c). The local FFT
analysis of these nanosized particles was performed and the patterns can be indexed as α-Fe (see the inset of Fig. 7b). The precipitation of nano-scaled α-Fe was probably resulted from the positively mixing enthalpy between Fe and Cu (13 kJ/mol). Therefore, a repulsive interaction should exist between Fe and Cu atoms, which contributed
to
the
nanocrystals
α-Fe
formation
[25].
The
present
(Fe77Mo5P9C7.5B1.5)99.9Cu0.1 BMG matrix composite exhibited two different scale of heterogeneous
structures;
the
micrometer-sized
α-Fe
dendrites
and
the
nanometer-sized α-Fe particles. The nanocrystal particles would probably act as the initiation sites for the multiple shear band initiation on the glassy matrix under compression, and the microscale α-Fe dendrites could strong interact with the shear bands during the shear bands propagation, which resulting the shear bands deflecting and branching. Therefore, the Fe-based BMG matrix composite with multi-scaled heterogeneous structures could effectively hinder the rapid instability of the shear banding and form a great number of the branching shear bands, leading to a distinctly enhanced on the room-temperature plasticity. However, the size of the nano-particles would increase with Cu addition as shown in the TEM images for x=0.5 at.% alloy in Fig. 8a. The size of α-Fe nanocrystal was around 20 nm (see Fig. 8b and Fig. 8c), which is above the shear bandwidth (10 nm) [26]. In contrast, large particles with a size above the shear bandwidth cannot have some effect on the shear band propagation. The shear band probably shear off when they encounter these nanocrystals, rather than block or circle, resulting a decrease of the plastic strain. This demonstrated that the room-temperature deformation ability of Fe-based BMG matrix composite was strongly related to the critical length scale of the microstructural heterogeneity [27], i.e., an appropriate of nano-scale and micro-scale α-Fe phases, leading to an enhanced plasticity by a combined effect of initiation and stability of shear bands. In additions, unlike the monolithic BMGs, the current Fe-based BMG matrix composites show the work hardening deformation behavior under room temperature, which may be due to a large amount of α-Fe is involved in plastic deformation. These results will open the way for designing of high performance Fe-based BMG matrix composite with multi-scaled
heterogeneous structures. 5 Conclusion In summary, in-situ formed (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) BMG matrix composites reinforced with microscale and nanoscale α-Fe phases have been successfully developed by copper mold casting using low purity raw materials. The (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 composite exhibits a record plasticity of 6.6% under the compression rod of 1.5 mm in diameter, together with high fracture strength of 3.1 GPa. The origin of the significant enhancement in plasticity is due to the combining effect from the initiation of shear bands and the stability of shear banding. The room-temperature deformation ability of Fe-based BMG matrix composite is strongly related to the critical length scale of the microstructural heterogeneity, i.e., nano-scale and micro-scale α-Fe phases. Our results will open the way for designing of high performance Fe-based BMG matrix composite using low purity raw materials for the engineering industry. Acknowledgements The authors would like to thank Dr. Feifei Zhang from University of Michigan for providing TEM assistance. This work was financially supported by the National Natural Science Foundation of China (Nos. 51671162 and 51301142), the Fundamental Research Funds for the Central Universities (No. XDJK2017B054) and Chongqing Research Program of Basic Research and Frontier Technology (No. cstc2015jcyjBX0107). References [1] W.L. Johnson, MRS Bull 32 (1999) 42-56. [2] A. Inoue, Acta Mater. 48 (2000) 279-306. [3] W.H. Wang, C. Dong, C.H. Shek, Mater. Sci. Eng. R. 44 (2004) 45-89. [4] W.L. Johnson. Nat. Mater. 14 (2015) 553-555.
[5] A. Inoue, Y. Shinohara, J.S. Gook, Mater. Trans. 36 (1995) 1427-1433. [6] A. Inoue, B.L. Shen, A.R. Yavari, A.L. Greer, J. Mater. Res. 18 (2003) 1487-1492. [7] C. Su, Y. Chen, P. Yu, M. Song , W. Chen, S.F. Guo, J. Alloys. Compd. 663 (2016) 867-871. [8] S.F. Guo, L. Liu, X. Lin, J. Alloys. Compd. 478 (2009) 226-228. [9] Z.P. Lu, C.T. Liu, J.R. Thompson, W.D. Porter, Phys. Rev. Lett. 92 (2004) 245503. [10] V. Ponnambalam, S.J. Poon, J. Mater. Res. 19 (2004) 1320-1323. [11] M. Stoica, J. Eckerta, S. Roth, Z.F. Zhang, L. Schultz, W.H. Wang, Intermetallics. 13 (2005) 764-769. [12] X.J. Gu, S.J. Poon, J. Mater. Res. 22 (2007) 344-351. [13] J.W. Qiao, H.L. Jia, P.K. Liaw, Mater. Sci. Eng. R. 100 (2016) 1-69. [14] C.C. Hays, C.P. Kim, W.L. Johnson, Phys. Rev. Lett. 84 (2000) 2091-2094. [15] D.C. Hofmann, J.Y. Suh, A. Wiest, M.L. Lind, M.D. Demetriou, W.L. Johnson, Proc. Natl. Acad. Sci. USA 105 (2008) 20136-20140. [16] Y.C. Kim, D.H. Kim, J.C. Lee, Mater. Trans. 44 (2003) 2224-2227. [17] H. Ma, J. Xu, E. Ma, Appl. Phys. Lett. 83 (2003) 2793-2795. [18] B.L. Shen, H. Men, A. Inoue, Appl. Phys. Lett. 89 (2006) 101915. [19] S.F. Guo, L. Liu, N. Li, Y. Li, Scripta Mater. 62 (2010) 329-332. [20] X. Li, H. Kato, K. Yubuta, A. Makino, A. Inoue, Mater. Sci. Eng. A. 527 (2010) 2598-2602. [21] S.F. Guo, J.L. Qiu, P. Yu, S.H. Xie, W. Chen, Appl. Phys. Lett. 105 (2014) 161901 [22] Y.H. Liu, G. Wang, R.J. Wang, D.Q. Zhao, M.X. Pan, W.H. Wang, Science 315 (2007) 1385-1388. [23] J.X. Zhao, R.T. Qu, F.F. Wu, Z.F. Zhang, B.L. Shen, M. Stoica, J. Eckert, J. Appl. Phys. 105 (2009) 103519 [24] S.F. Guo, N. Li, C. Zhang, L. Liu, Journal of Alloys and Compounds 504 (2010) 78 [25] A. Makino, X. Li, K. Yubuta, C.T. Chang, T. Kubota, A. Inoue, Scripta Mater. 60 (2009) 277-280 [26] J. Li, F. Spaepen, T.C. Hufnagel, Philos. Mag. A 82 (2002) 2623-2630. [27] J.M. Park, D.H. Kim, M. Stoica, N. Mattern, R. Li, J. Eckert. J. Mater. Res. 26 (2011) 2080-2086.
Figure captions
Fig. 1 The XRD patterns of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7 and 1 at.%) alloy.
Fig. 2 The DSC curves of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7 and 1 at.%) alloys at a heat rate of 20 K/min, respectively.
Fig.
3
The
SEM
backscattered
electron
images
of
(Fe77Mo5P9C7.5B1.5)100-xCux alloys with different Cu. (a) x=0; (b) x=0.1; (c) x=0.3; (d) x=0.5; (e) x=0.7; (f) x=1.
Fig. 4 The strain-stress curves of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloy rod with a diameter of 1.5 mm under room-temperature compression.
Fig. 5 The SEM images of fractured (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy. Fig. 6 The TEM images of Fe77Mo5P9C7.5B1.5 alloy (a); the corresponding high-resolution TEM images of dendrites (b) and the matrix (c), respectively.
Fig. 7 The TEM images of (Fe77Mo5P9C7.5B1.5)99.9Cu0.1 alloy (a), and the high-resolution TEM images showing the nanocrystal size from 1 nm (b) to 10 nm (c).
Fig. 8 The TEM images of (Fe77Mo5P9C7.5B1.5)99.5Cu0.5 alloy.
Table 1 The thermal characteristics and mechanical properties of (Fe77Mo5P9C7.5B1.5)100-xCux (x=0, 0.1, 0.3, 0.5, 0.7, 1 at.%) alloys. Alloy
Tg/K
Tx/K
ΔTx/K
ΔH(J/g)
σy (MPa)
σmax (MPa)
ɛ p (%)
x=0
729
790
61
-34.4
2300
2900
3.9
x=0.1
721
778
57
-28.3
2450
3100
6.6
x=0.3
726
772
46
-27.1
2270
2900
3.5
x=0.5
726
773
47
-16.4
2170
2800
0.9
x=0.7
714
777
63
-9.8
2500
2500
-
x=1
-
-
-
-
2100
2100
-
Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8