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A new method of synthesizing ultrafine vanadium carbide by dielectric barrier discharge plasma assisted milling
Int. Journal of Refractory Metals and Hard Materials 30 (2012) 48–50
Contents lists available at ScienceDirect
Int. Journal of Refractory Metals and Hard Materials j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / I J R M H M
A new method of synthesizing ultrafine vanadium carbide by dielectric barrier discharge plasma assisted milling L.Y. Dai a, b, S.F. Lin a, J.F. Chen a, M.Q. Zeng b, M. Zhu b,⁎ a b
Marine Engineering Institute, Jimei University, Xiamen 361021, China School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
a r t i c l e
i n f o
Article history: Received 28 March 2011 Accepted 11 July 2011 Keywords: Dielectric barrier discharge plasma (DBDP) Mechanical milling Vanadium carbide
a b s t r a c t A new high efficiency method of synthesis of ultrafine vanadium carbide (VC) at a low carburization temperature has been developed. Firstly, a mixture of V2O5 and graphite powders is milled using dielectric barrier discharge plasma assisted milling (denoted as DBDP milling) for 4 h, and then the milled powders are carburized at 1200 °C, causing the V2O5 to react completely with graphite to form ultrafine VC. The formation temperature of VC is much lower than that needed in the conventional milling and heating process. This is because of the greatly enhanced reaction between V2O5 and graphite arising from the unique lump-like morphology and large number of clean surface contacts and greater surface area induced by DBDP milling. © 2011 Elsevier Ltd. All rights reserved.
1. Introduction Vanadium carbide is an extremely hard refractory ceramic material with unique properties of high hardness, high temperature strength, and high chemical stability. VC has found various industrial applications in powder metallurgy, for example as an additive to tungsten carbide to inhibit the grain growth of carbide and thus improve the property of cermets. Generally, VC is synthesized through various high temperature reactions [1], such as the low pressure reaction of vanadium hydride with carbon in a reducing atmosphere at 2000 °C, or the vacuum reaction between elemental vanadium and carbon powders at temperatures ranging from 1100 °C to 1500 °C. Obviously, these fabrication conditions are relatively strict and also consume a large amount of energy. Therefore, a more efficient and cheaper synthesis of VC is needed. In recent years, mechanical alloying (MA) has been applied to prepare vanadium carbide powders in different ways. For example, Calka et al. prepared VC and V2C by ball milling elemental vanadium and graphite for 70 h [2]; Zhang et al. prepared V8C7 by milling a mixture of V2O5, Mg and graphite for 48 h and then conducting carburization treatment at 950 °C [3]. However, the fabrication efficiency of VC is low with the traditional MA technique because of the long milling times, which also cause serious Fe contamination. Recently, it has been shown that ball milling assisted by external energy fields can effectively promote powder refining and solid-state reaction [4–7]. The authors of the present paper have also developed a Abbreviations: VC, vanadium carbide; MA, mechanical alloying; DBDP, dielectric barrier discharge plasma assisted milling. ⁎ Corresponding author. Tel.: + 86 20 87113924. E-mail address: [email protected] (M. Zhu). 0263-4368/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2011.07.002
new kind of vibratory mill in which dielectric barrier discharge plasma (DBDP) is introduced [8]. We have synthesized nano-sized tungsten carbide from elemental tungsten and graphite powders by DBDP milling and subsequent carburization [9]. This fabrication process for WC has the advantages of shorter milling time (only 3 h) and lower carbonization temperature (1000 °C) compared to the traditional method. This increased efficiency is attributed to the synergism of mechanical milling and plasma in DBDP milling. The present investigation extends DBDP milling to the synthesis of VC, and explores a new lower-cost, higher-efficiency route. We demonstrate that DBDP milling of a powder mixture of V2O5 and graphite indeed enhances their mutual reaction and leads to improved formation of VC at a lower temperature. 2. Materials and methods V2O5 (99.0% purity, particle size 30 μm) and graphite (99.9% purity, particle size 30 μm) powders were mixed at an atomic ratio of 1:7. The powder mixture (150 g) and hardened steel balls with a ball-topowder weight ratio of 1:50 were sealed in a cylindrical stainless steel vial. 5 ml of ethanol was added into the mixed powders as a process control agent. In the milling process, the vial was evacuated and then backfilled with high purity argon (0.1 MPa), and the vial was then vibrated at a double amplitude of 10 mm and a frequency of 25 Hz. The dielectric barrier discharge plasma was generated by 24 kV of high-voltage alternating current at a frequency of 14 kHz. A Netzsch STA409PC differential scanning calorimeter (DSC), a Philips X'Pert MPD X-ray diffractometer (XRD) using Cu-Kα radiation, an ASAP 2010 Micromeritics specific surface area analyzer, a LEO 1530 VP scanning electron microscope (SEM) and a JEOL-2010 transmission electron microscope (TEM) were used to characterize the
L.Y. Dai et al. / Int. Journal of Refractory Metals and Hard Materials 30 (2012) 48–50
49
Fig. 1. SEM images of a) V2O5 un-milled and b) V2O5-C powders DBDP-milled for 4 h.
structural and microstructural changes in the powders. The DSC measurement was performed under Ar protection at a heating rate of 20 K/min. 3. Results and discussion Fig. 1(a) and (b) shows the SEM morphologies of the original V2O5 powders and the V2O5-C powders DBDP milled for 4 h, respectively. The original V2O5 powders were spicular with length of about 30 μm. After DBDP milling, the morphology of the V2O5-C powders had changed markedly to a lump-like structure in which the particles were actually agglomerates of smaller primitive particles of about 300 nm in size. Similar morphological features were also previously found for DBDP-milled W-C powders [9]. The lump-like V2O5-C particles also show a melting phenomenon similar to that seen in the DBDP-milled W-C powders, suggesting that significant heating effect is associated with DBDP milling. The continuous welding and fracturing of particles during DBDP milling enables the V2O5-C powder particles to repeatedly form close contacts with one another and creates a large amount of clean interfaces and surfaces. The specific surface area of DPDB-milled V2O5-C powders was determined to be 105.9 m 2/g, which is much higher than the value of 66.6 m 2/g for a V2O5-C powder sample treated by conventional milling for 4 h. The above morphological features and higher specific surface area are related to the synergism of the thermal explosions and mechanical impacts induced by the DBDP milling, as discussed in our previous work [9,10]. Fig. 2 shows the TG and DSC heating scan curves of 4 h DBDP milled V2O5-C powders. The variation of weight loss of the sample in the TG curve indicates the reduction reaction kinetics. As shown in the TG curve, continuous weight loss suggests the conversion of V2O5 follows the principle of step by step reduction and accompanying release of carbon monoxide. When the temperature exceeds the melting point of V2O5 (690 °C), the weight loss curve declines more steeply because of volatilization of V2O5. The exothermic peaks in the DSC curve also indicate the multi-step deoxidizing reaction characteristics of V2O5. Since the purpose of this work is to reveal the
Fig. 2. DTA and DSC heating scan curves of V2O5-C powders DBDP-milled for 4 h.
synthesis of VC and its microstructural features, we did not investigate the details of each reaction step corresponding to the peaks in DSC curve. Only the product obtained after DSC heating to 1200 °C was studied by XRD, SEM and TEM. The XRD patterns of the V2O5-C powder mixtures are given in Fig. 3. The starting materials are a mixture of coarse-grained V2O5 and C powders, as characterized by the sharp diffraction peaks of V2O5 shown in Fig. 3a, and noting that diffraction peaks of graphite were hardly observed owing to its small scattering factor. After 4 h of DBDP milling, the diffraction peaks of V2O5 broadened and the high-angle diffraction peaks vanished (Fig. 3b) as a result of grain refinement and increase in lattice distortion. However, no VC or other new phases were detected by XRD. Fig. 3c and d compares the XRD patterns of V2O5-C powders after conventional milling or DBDP milling for 4 h, followed by heating to 1200 °C during the DSC scan. In both samples, the VC phase can be identified. A single VC phase is observed for the DBDP milled V2O5-C powders, while traces of V8C7 and V2O3 are observed in addition to VC in the V2O5-C powders treated by conventional milling. The existence of V8C7 and V2O3 means that the carbonization reaction is incomplete for the conventionally milled V2O5-C powders even at 1200 °C.
Fig. 3. XRD patterns of V2O5-C powders: (a) un-milled and (b) DBDP-milled for 4 h; and the V2O5-C powders after DSC heating to 1200 °C following: (c) conventional milling and (d) DBDP milling for 4 h.
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Fig. 4. SEM and TEM images of VC obtained by heating V2O5-C powders at 1200 °C after DBDP milling for 4 h, (a) and (b) are SEM images with different magnifications, (c) and (d) are the TEM bright field and dark field images, respectively. The inset in Fig. 4 shows the selected area diffraction pattern of VC phase.
We have shown that DBDP milling strongly enhances the synthesis of VC with respect to conventional milling. This should be attributed to the unique effects of this type of milling and the resultant microstructural features summarized as follows: (1) During DBDP milling, the V2O5 and C powders were refined rapidly and mixed homogeneously to form a composite structure with a higher specific surface area; and (2) the DBDP bombardment generates a quasistatic thermal stress and a dynamic thermal stress to create radicals and excited particles [11]. Therefore, the V2O5-C powder mixtures are highly activated by DBDP, creating many more sites for nucleation or reaction of VC formation, and also shortening the diffusion distances required for its growth. As shown in Fig. 4, SEM and TEM analysis further reveals the morphology and microstructure of the VC obtained by DBDP milling and subsequent carburization at 1200 °C of the V2O5-C powders. The agglomerated VC particles (Fig. 4a) have a lump-like morphology with a planar size of 50–200 nm (Fig. 4b). The inset of selected area electron diffraction pattern (Fig. 4d) verifies the existence of VC phase, while the TEM bright field image (Fig. 4c) and the dark field image (Fig. 4d) further shows that the VC obtained is also ultrafine in grain size. 4. Conclusions In summary, we have shown that DBDP milling can effectively activate the V2O5-C powders and enhance the deoxidation reaction at a relatively low temperature; ultrafine VC particles are obtained. In comparison with the fabricating process using conventional milling and carburization, DBDP milling requires a much shorter milling time (4 h) and lower carburization temperature (1200 °C). This result further illustrates the advantages of DBDP milling for the synthesis of hard materials.
Acknowledgements This work was supported by the Nature Science Foundation of Fujian Province (No. E0810024), the Science & Technology project from Educational Commission of Fujian Province (No. JA09150), the Science & Technology Major Subject of Fujian Province (No. 2008HZ0002-1) and the Scientific and Technical Personnel Serving Enterprise Project of Ministry of Finance and Ministry of Science & Technology (Financial Education [2009] No. 365).
References [1] Gupta CK, Krishnamurthy N. Extractive metallurgy of vanadium. Amsterdam: Elsevier; 1992. [2] Calka A, Kaczmarek WA. The effect of milling conditions on the formation of nanostructures: synthesis of vanadium carbides. Scripta Metall Mater 1992;26: 249–53. [3] Zhang B, Li ZQ. Synthesis of vanadium carbide by mechanical alloying. J Alloys Compd 2005;392:83–6. [4] Mordyuk BN, Prokopenko GI. Mechanical alloying of powder materials by ultrasonic milling. Ultrasonics 2004;42:43–6. [5] Radlinski AP, Calka A. Mechanical alloying of high melting point intermetallics. Mater Sci Eng A 1991;134:1376–9. [6] Calka A, Wexler D. Mechanical milling assisted by electrical discharge. Nature 2002;419:147–51. [7] Huang B, Perez RJ, Lavernia EJ, Luton MJ. Formation of supersaturated solid solutions by mechanical alloying. Nanostruct Mater 1996;7:67–79. [8] Zhu M, Dai LY, Cao B, Ouyang LZ. China Patent: ZL 200510036231.9, 2007.08.29. [9] Zhu M, Dai LY, Gu NS, Cao B, Ouyang LZ. Synergism of mechanical milling and dielectric barrier discharge plasma on the fabrication of nano-powders of pure metals and tungsten carbide. J Alloys Compd 2009;478:624–9. [10] Dai LY, Cao B, Zhu M. Comparison on refinement of iron powder by ball milling assisted by different external field. Acta Metall Sinica 2006;19:411–5. [11] Qin Y, Zou JX, Dong C, Wang XG, Wu AM, Liu Y, et al. Temperature-stress fields and related phenomena induced by a high current pulsed electron beam. Nucl Instrum Meth Phys Res Sect B 2004;225:544–54.
Contents lists available at ScienceDirect
Int. Journal of Refractory Metals and Hard Materials j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / I J R M H M
A new method of synthesizing ultrafine vanadium carbide by dielectric barrier discharge plasma assisted milling L.Y. Dai a, b, S.F. Lin a, J.F. Chen a, M.Q. Zeng b, M. Zhu b,⁎ a b
Marine Engineering Institute, Jimei University, Xiamen 361021, China School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
a r t i c l e
i n f o
Article history: Received 28 March 2011 Accepted 11 July 2011 Keywords: Dielectric barrier discharge plasma (DBDP) Mechanical milling Vanadium carbide
a b s t r a c t A new high efficiency method of synthesis of ultrafine vanadium carbide (VC) at a low carburization temperature has been developed. Firstly, a mixture of V2O5 and graphite powders is milled using dielectric barrier discharge plasma assisted milling (denoted as DBDP milling) for 4 h, and then the milled powders are carburized at 1200 °C, causing the V2O5 to react completely with graphite to form ultrafine VC. The formation temperature of VC is much lower than that needed in the conventional milling and heating process. This is because of the greatly enhanced reaction between V2O5 and graphite arising from the unique lump-like morphology and large number of clean surface contacts and greater surface area induced by DBDP milling. © 2011 Elsevier Ltd. All rights reserved.
1. Introduction Vanadium carbide is an extremely hard refractory ceramic material with unique properties of high hardness, high temperature strength, and high chemical stability. VC has found various industrial applications in powder metallurgy, for example as an additive to tungsten carbide to inhibit the grain growth of carbide and thus improve the property of cermets. Generally, VC is synthesized through various high temperature reactions [1], such as the low pressure reaction of vanadium hydride with carbon in a reducing atmosphere at 2000 °C, or the vacuum reaction between elemental vanadium and carbon powders at temperatures ranging from 1100 °C to 1500 °C. Obviously, these fabrication conditions are relatively strict and also consume a large amount of energy. Therefore, a more efficient and cheaper synthesis of VC is needed. In recent years, mechanical alloying (MA) has been applied to prepare vanadium carbide powders in different ways. For example, Calka et al. prepared VC and V2C by ball milling elemental vanadium and graphite for 70 h [2]; Zhang et al. prepared V8C7 by milling a mixture of V2O5, Mg and graphite for 48 h and then conducting carburization treatment at 950 °C [3]. However, the fabrication efficiency of VC is low with the traditional MA technique because of the long milling times, which also cause serious Fe contamination. Recently, it has been shown that ball milling assisted by external energy fields can effectively promote powder refining and solid-state reaction [4–7]. The authors of the present paper have also developed a Abbreviations: VC, vanadium carbide; MA, mechanical alloying; DBDP, dielectric barrier discharge plasma assisted milling. ⁎ Corresponding author. Tel.: + 86 20 87113924. E-mail address: [email protected] (M. Zhu). 0263-4368/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2011.07.002
new kind of vibratory mill in which dielectric barrier discharge plasma (DBDP) is introduced [8]. We have synthesized nano-sized tungsten carbide from elemental tungsten and graphite powders by DBDP milling and subsequent carburization [9]. This fabrication process for WC has the advantages of shorter milling time (only 3 h) and lower carbonization temperature (1000 °C) compared to the traditional method. This increased efficiency is attributed to the synergism of mechanical milling and plasma in DBDP milling. The present investigation extends DBDP milling to the synthesis of VC, and explores a new lower-cost, higher-efficiency route. We demonstrate that DBDP milling of a powder mixture of V2O5 and graphite indeed enhances their mutual reaction and leads to improved formation of VC at a lower temperature. 2. Materials and methods V2O5 (99.0% purity, particle size 30 μm) and graphite (99.9% purity, particle size 30 μm) powders were mixed at an atomic ratio of 1:7. The powder mixture (150 g) and hardened steel balls with a ball-topowder weight ratio of 1:50 were sealed in a cylindrical stainless steel vial. 5 ml of ethanol was added into the mixed powders as a process control agent. In the milling process, the vial was evacuated and then backfilled with high purity argon (0.1 MPa), and the vial was then vibrated at a double amplitude of 10 mm and a frequency of 25 Hz. The dielectric barrier discharge plasma was generated by 24 kV of high-voltage alternating current at a frequency of 14 kHz. A Netzsch STA409PC differential scanning calorimeter (DSC), a Philips X'Pert MPD X-ray diffractometer (XRD) using Cu-Kα radiation, an ASAP 2010 Micromeritics specific surface area analyzer, a LEO 1530 VP scanning electron microscope (SEM) and a JEOL-2010 transmission electron microscope (TEM) were used to characterize the
L.Y. Dai et al. / Int. Journal of Refractory Metals and Hard Materials 30 (2012) 48–50
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Fig. 1. SEM images of a) V2O5 un-milled and b) V2O5-C powders DBDP-milled for 4 h.
structural and microstructural changes in the powders. The DSC measurement was performed under Ar protection at a heating rate of 20 K/min. 3. Results and discussion Fig. 1(a) and (b) shows the SEM morphologies of the original V2O5 powders and the V2O5-C powders DBDP milled for 4 h, respectively. The original V2O5 powders were spicular with length of about 30 μm. After DBDP milling, the morphology of the V2O5-C powders had changed markedly to a lump-like structure in which the particles were actually agglomerates of smaller primitive particles of about 300 nm in size. Similar morphological features were also previously found for DBDP-milled W-C powders [9]. The lump-like V2O5-C particles also show a melting phenomenon similar to that seen in the DBDP-milled W-C powders, suggesting that significant heating effect is associated with DBDP milling. The continuous welding and fracturing of particles during DBDP milling enables the V2O5-C powder particles to repeatedly form close contacts with one another and creates a large amount of clean interfaces and surfaces. The specific surface area of DPDB-milled V2O5-C powders was determined to be 105.9 m 2/g, which is much higher than the value of 66.6 m 2/g for a V2O5-C powder sample treated by conventional milling for 4 h. The above morphological features and higher specific surface area are related to the synergism of the thermal explosions and mechanical impacts induced by the DBDP milling, as discussed in our previous work [9,10]. Fig. 2 shows the TG and DSC heating scan curves of 4 h DBDP milled V2O5-C powders. The variation of weight loss of the sample in the TG curve indicates the reduction reaction kinetics. As shown in the TG curve, continuous weight loss suggests the conversion of V2O5 follows the principle of step by step reduction and accompanying release of carbon monoxide. When the temperature exceeds the melting point of V2O5 (690 °C), the weight loss curve declines more steeply because of volatilization of V2O5. The exothermic peaks in the DSC curve also indicate the multi-step deoxidizing reaction characteristics of V2O5. Since the purpose of this work is to reveal the
Fig. 2. DTA and DSC heating scan curves of V2O5-C powders DBDP-milled for 4 h.
synthesis of VC and its microstructural features, we did not investigate the details of each reaction step corresponding to the peaks in DSC curve. Only the product obtained after DSC heating to 1200 °C was studied by XRD, SEM and TEM. The XRD patterns of the V2O5-C powder mixtures are given in Fig. 3. The starting materials are a mixture of coarse-grained V2O5 and C powders, as characterized by the sharp diffraction peaks of V2O5 shown in Fig. 3a, and noting that diffraction peaks of graphite were hardly observed owing to its small scattering factor. After 4 h of DBDP milling, the diffraction peaks of V2O5 broadened and the high-angle diffraction peaks vanished (Fig. 3b) as a result of grain refinement and increase in lattice distortion. However, no VC or other new phases were detected by XRD. Fig. 3c and d compares the XRD patterns of V2O5-C powders after conventional milling or DBDP milling for 4 h, followed by heating to 1200 °C during the DSC scan. In both samples, the VC phase can be identified. A single VC phase is observed for the DBDP milled V2O5-C powders, while traces of V8C7 and V2O3 are observed in addition to VC in the V2O5-C powders treated by conventional milling. The existence of V8C7 and V2O3 means that the carbonization reaction is incomplete for the conventionally milled V2O5-C powders even at 1200 °C.
Fig. 3. XRD patterns of V2O5-C powders: (a) un-milled and (b) DBDP-milled for 4 h; and the V2O5-C powders after DSC heating to 1200 °C following: (c) conventional milling and (d) DBDP milling for 4 h.
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Fig. 4. SEM and TEM images of VC obtained by heating V2O5-C powders at 1200 °C after DBDP milling for 4 h, (a) and (b) are SEM images with different magnifications, (c) and (d) are the TEM bright field and dark field images, respectively. The inset in Fig. 4 shows the selected area diffraction pattern of VC phase.
We have shown that DBDP milling strongly enhances the synthesis of VC with respect to conventional milling. This should be attributed to the unique effects of this type of milling and the resultant microstructural features summarized as follows: (1) During DBDP milling, the V2O5 and C powders were refined rapidly and mixed homogeneously to form a composite structure with a higher specific surface area; and (2) the DBDP bombardment generates a quasistatic thermal stress and a dynamic thermal stress to create radicals and excited particles [11]. Therefore, the V2O5-C powder mixtures are highly activated by DBDP, creating many more sites for nucleation or reaction of VC formation, and also shortening the diffusion distances required for its growth. As shown in Fig. 4, SEM and TEM analysis further reveals the morphology and microstructure of the VC obtained by DBDP milling and subsequent carburization at 1200 °C of the V2O5-C powders. The agglomerated VC particles (Fig. 4a) have a lump-like morphology with a planar size of 50–200 nm (Fig. 4b). The inset of selected area electron diffraction pattern (Fig. 4d) verifies the existence of VC phase, while the TEM bright field image (Fig. 4c) and the dark field image (Fig. 4d) further shows that the VC obtained is also ultrafine in grain size. 4. Conclusions In summary, we have shown that DBDP milling can effectively activate the V2O5-C powders and enhance the deoxidation reaction at a relatively low temperature; ultrafine VC particles are obtained. In comparison with the fabricating process using conventional milling and carburization, DBDP milling requires a much shorter milling time (4 h) and lower carburization temperature (1200 °C). This result further illustrates the advantages of DBDP milling for the synthesis of hard materials.
Acknowledgements This work was supported by the Nature Science Foundation of Fujian Province (No. E0810024), the Science & Technology project from Educational Commission of Fujian Province (No. JA09150), the Science & Technology Major Subject of Fujian Province (No. 2008HZ0002-1) and the Scientific and Technical Personnel Serving Enterprise Project of Ministry of Finance and Ministry of Science & Technology (Financial Education [2009] No. 365).
References [1] Gupta CK, Krishnamurthy N. Extractive metallurgy of vanadium. Amsterdam: Elsevier; 1992. [2] Calka A, Kaczmarek WA. The effect of milling conditions on the formation of nanostructures: synthesis of vanadium carbides. Scripta Metall Mater 1992;26: 249–53. [3] Zhang B, Li ZQ. Synthesis of vanadium carbide by mechanical alloying. J Alloys Compd 2005;392:83–6. [4] Mordyuk BN, Prokopenko GI. Mechanical alloying of powder materials by ultrasonic milling. Ultrasonics 2004;42:43–6. [5] Radlinski AP, Calka A. Mechanical alloying of high melting point intermetallics. Mater Sci Eng A 1991;134:1376–9. [6] Calka A, Wexler D. Mechanical milling assisted by electrical discharge. Nature 2002;419:147–51. [7] Huang B, Perez RJ, Lavernia EJ, Luton MJ. Formation of supersaturated solid solutions by mechanical alloying. Nanostruct Mater 1996;7:67–79. [8] Zhu M, Dai LY, Cao B, Ouyang LZ. China Patent: ZL 200510036231.9, 2007.08.29. [9] Zhu M, Dai LY, Gu NS, Cao B, Ouyang LZ. Synergism of mechanical milling and dielectric barrier discharge plasma on the fabrication of nano-powders of pure metals and tungsten carbide. J Alloys Compd 2009;478:624–9. [10] Dai LY, Cao B, Zhu M. Comparison on refinement of iron powder by ball milling assisted by different external field. Acta Metall Sinica 2006;19:411–5. [11] Qin Y, Zou JX, Dong C, Wang XG, Wu AM, Liu Y, et al. Temperature-stress fields and related phenomena induced by a high current pulsed electron beam. Nucl Instrum Meth Phys Res Sect B 2004;225:544–54.