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Microstructure of nanometer Al2O3 particles reinforced aluminum matrix composites processed by high pulsed electromagnetic field
Materials Letters 99 (2013) 50–53
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Microstructure of nanometer Al2O3 particles reinforced aluminum matrix composites processed by high pulsed electromagnetic field Guirong Li a,b,c,n, Hongming Wang a, Xueting Yuan a, Yutao Zhao a a
School of Materials Science & Engineering, Jiangsu University, Zhenjiang 212013, PR China The State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai 200240, PR China c Key Laboratory of Cryogenics, TIPC, Chinese Academy of Sciences, Beijing 100190, PR China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 January 2013 Accepted 21 February 2013 Available online 1 March 2013
The as-cast in situ Al2O3 particles reinforced aluminum matrix composites were subjected to the impact treatment due to the Lorentz force generated by high pulsed electromagnetic field. The magnetic induced intensity (B) was set as 1 T, 2 T and 3 T. Transmission electronic microscopy observation shows that the impact has induced the elastic deformation in materials that results in the enhancement of dislocation density. The value increases from 2.2 1011/m2 in as-cast sample to 8.9 1013/m2 in the 3 T treated one. Besides, stacking faults and deformation twins with 3, 4, 6 atomic planes can also be seen. The results demonstrate that high pulsed electromagnetic field is an efficient and economical approach to acquire a specific microstructure and, meanwhile, keep the original shape of sample. & 2013 Elsevier B.V. All rights reserved.
Keywords: Composite materials Microstructure
1. Introduction In the past decades, many attentions have been paid to the combination of electromagnetic field with new processing of advanced materials, together with the emergence of a novel concept as EPM (Electromagnetic Processing of Materials). In most cases, both the force and heat effect of electromagnetic fields were employed to influence the hyperthermia fabricating process of materials [1], the grain refining during solidification [2], phase transformation [3] and sometimes the heat treatment [4]. But the effect of high electromagnetic field on the structural evolution of solid metal/alloy at room temperature has scarcely reported. Based on the theoretical analysis, the impact effect of Lorentz force induced by high electromagnetic field is big enough to result in the deformation of metal. Hopefully a high electromagnetic field will take a positive role in the structural evolution of some solid material. In this paper a prepared Al2O3 particles reinforced aluminum matrix composite was subjected to a specific impact by high pulsed electromagnetic field (HPEMF) at different magnetic induced intensity (B). The structural evolution and mechanisms have been revealed and further discussed in detail. The Al2O3 particles reinforced aluminum matrix composites exhibit the characteristics of nanometer particles and uniform distribution of particles in matrix, which has focused the attentions of some researchers. Due to a group of available reports the
n Corresponding author at: Jiangsu University, School of Materials Science & Engineering, 301 Xurfu Road, Zhenjiang 212013, PR China. Tel.: þ86 51 188 789 850. E-mail address: [email protected] (G. Li).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.02.089
comparison will be easily conducted among microstructures resulted from different treatment process.
2. Materials and processing In situ 1 vol% Al2O3 particles reinforced aluminum matrix composites were fabricated in advance via direct melt reaction method [5]. The as-cast composites were processed into flakes with the size of 20 mm 20 mm 2 mm. They were placed and fixed onto a refractory block with several slots. A refractory with little susceptibility would not interfere with the load-carrying of samples. Fig. 1 showed the sample status and relationship with the HPEMF, where P was the magnetic pressure and J the induced current. Then the samples were subjected to the impact treatment by HPEMF, aiming to search for a new approach to acquire a specific microstructure to improve the properties of materials, meanwhile, not to affect the original shape of samples. The levels of B were set as 1 T, 2 T and 3 T and the imposed pulse number was 30 in total. The processing parameters have been illustrated in Fig. 2, where IO and UO meant the output current and voltage of electric controller. High-resolution transmission electron microscopy (HRTEM) investigations were carried out with a JEOL-2100F TEM. The values of B were tested preciously by a LZ-610H Tesla meter.
3. Results and discussions Fig. 3 shows the particle distribution and dislocation morphology of as-cast and HPEMF-treated samples at different B values. The
G. Li et al. / Materials Letters 99 (2013) 50–53
in situ Al2O3 particles distribute uniformly in the matrix. The average sizes of them are in the range of 30–50 nm. In the as-cast sample there are only a few dislocations, some of which exist along or around the particles (Fig. 3a). But high density and various dislocations can be seen in the three HPEMF-treated samples at different B. Just as we know, the generation of high density dislocations is often the result of tensile or compressed deformation [6]. When B¼ 1 T and P¼0.79 MPa, the generated dislocation exhibits banded shape and 3.8 1012/m2 density that is 16.3 times in comparison to the value of 2.2 1011/m2 in as-cast sample(Fig. 3b). At the condition of B¼2 T and P¼3.17 MPa, the dislocation density further adds up to 6.7 1013/m2. When the dislocation moves forward rapidly and comes across an alumina
F
J
particle, it will circle around the particle and its shape will change from banded to hooped one, together with the increase of dislocation density (Fig. 3c). When B¼3 T and P¼7.14 MPa, the dislocation density increase continuously till to 8.9 1013/m2 (Fig. 3d). If compared to the value at 2 T the amplification is not apparent as before. On this occasion the increment of dislocation are attributed to the deformation induced by the Lorentz force effect of HPEMF. The magnetic pressure P can be expressed and calculated by Eq. (1) [7], where m0 is the magnetic conductivity of composites as 1.26 10 6 H/m. P¼
B2
ð1Þ
m0
So P equals to 7.14 MPa corresponding to B is 3 T. In comparison to the 8.35 MPa yield strength of Al2O3p/Al composites (a tested value) the samples processed by HPEMF are subjected to an elastic deformation. If B is larger than 3.23 T the P will be larger than 8.35 MPa the elastic deformation will convert to a plastic one and the sample cannot keep its original shape. In each cycle the peak impact lasts for about 1.1 s. Upon receiving the strong and instantaneous impact in a form of compression stress the sample will deform elastically, then recovers to its original state in a form of tension stress when the impact passes. The repeating 30 cycles with alternant compression and tension stress are attributed to the elastic deformation and dislocation behavior. Fig. 4 demonstrates the HRTEM diagrams of the above four samples in one grain. The incident direction is ½1 1 0. In the ascast sample the atoms are in an aligned array. No apparent disordered atomic arrays can be observed. In Fig. 4b there are two areas displaying the disordered atomic arrays and testifying the elastic deformation in composites. In Fig. 4c, besides one area showing the disordered atomic array, there is an apparent directional change of atomic array about 1451. In Fig. 4d the stacking fault (SF) and deforming twin (DT) can be found. In fcc metals, because of energy considerations, dislocations with strengths larger than unity are generally unstable and tend to dissociate into two or more dislocations of lower strength. SFs and DTs can
(a) B
51
B
S A M P L E
Refractory Block Fig. 1. The sample status and relationship with the electromagnetic field.
1.1 s
……
1T Io=4A
Magnetic induced intensity, T
UO=1.0V
30 cycles in total Time, s
(One cycle takes 2.8s) …… 2T
1.1 s Io=4A UO=1.2V
30 cycles in total Time, s
(One cycle takes 3.5s) 3T
……
1.1 s
Io=4.1A UO=1.5V (One cycle takes 4.3s) Fig. 2. The magnetic parameters of HPEMF at different B.
Time, s
.2
52
G. Li et al. / Materials Letters 99 (2013) 50–53
Fig. 3. TEM photograph of as-cast sample (a) and those treated at different B; (b) 1T; (c) 2T; (d) 3T.
Fig. 4. HRTEM diagram of samples at different states (a) as-cast; (b) 1T; (c) 2T; (d) 3T.
G. Li et al. / Materials Letters 99 (2013) 50–53
be formed from the dissociation of either screw dislocations [8]. SFs formed by two 301 Shockley partials dissociated from end-on 01 screw dislocations were frequently observed in the severe plastic deformed alloy [9]. While in the HPEMF-treated composites, SFs induced by the pulsed impact has never been reported in previous literatures. It is deduced that, in some sense, the effect of HPEMF is similar to the severe plastic deformation. For the formation mechanism of DTs, they are attributed to the dynamic overlapping of several SFs of dissociated dislocations on adjacent slip planes. The twin can grow thicker from three (DT1), four (DT3) to six atomic planes (DT2 in Fig. 4d) by adding more SFs on either side of the twin [10]. Furthermore, as indicated in Fig. 4d, high density dislocations are present around the twin boundary. Assuming that the electron beam and dislocation line are parallel to ½1 1 0 incident direction, these dislocations are determined to be on the ð1 1 1Þ plane with Burgers vectors of 1/2[1 0 1]. They are believed to be associated with the twin formation process. These results suggest that partial dislocation emission in fcc metals could also become a deformation mechanism in HPEMF treated aluminum.
4. Conclusions Upon receiving the magnetic pulsed impact by HPEMF the Al2O3p/Al composites will deform elastically due to the magnetic Lorentz force. The dislocation density increases with the increase of B in the range of 1–3 T. In the 3 T treated sample stacking faults
53
and deformation twins with 3, 4, 6 atomic planes can be seen. In summary, HPEMF is an efficient and economical approach to acquire a specific microstructure similar to severe plastic deformation, but still can, meanwhile, keep the original shape of sample.
Acknowledgments This work was financially supported by the NSFC (51001054, 51174099, 51174098), Natural Science Foundation of Jiangsu Province (BK2011533), open funds of SKLMMC of SJTU(mmckf12-06), Key lab of Cryogenics, TIPC-CAS (CRYO201106) and National Science Foundation for post-doctors and Jiangsu’s (20100471382, 1001023C).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Li GR, Zhao YT. J Uni Sci Technol Beijing 2007;14:460–3. Li X, Ren ZM. J Mater Proc Tech 2008;195:125–34. Wang B, Yang YS, Sun ML. Trans Nonferrous Met Soc China 2012;20:1685–90. Akhbarizadeh A, Amini K, Javadpour S. Mater Des 2012;41:114–23. Li GR, Wang HM. Trans Nonferrous Met Soc China 2010;18:577–83. Li GR, Zhang XY. Adv Mater Res 2011;284–286:2280–3. Liu MP, Roven HJ, Yu YD. Int J Mater Res 2007;98:184–90. Yamakov V, Wolf D, Phillpot SR. Acta Mater 2002;50:5005–20. Zhou SJ, Perston DL. Science 1998;279:1525–7. Patel A, Das S, Prasad BK. Mater Sci Eng A 2011;530:225–32.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Microstructure of nanometer Al2O3 particles reinforced aluminum matrix composites processed by high pulsed electromagnetic field Guirong Li a,b,c,n, Hongming Wang a, Xueting Yuan a, Yutao Zhao a a
School of Materials Science & Engineering, Jiangsu University, Zhenjiang 212013, PR China The State Key Laboratory of Metal Matrix Composites, Shanghai Jiaotong University, Shanghai 200240, PR China c Key Laboratory of Cryogenics, TIPC, Chinese Academy of Sciences, Beijing 100190, PR China b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 January 2013 Accepted 21 February 2013 Available online 1 March 2013
The as-cast in situ Al2O3 particles reinforced aluminum matrix composites were subjected to the impact treatment due to the Lorentz force generated by high pulsed electromagnetic field. The magnetic induced intensity (B) was set as 1 T, 2 T and 3 T. Transmission electronic microscopy observation shows that the impact has induced the elastic deformation in materials that results in the enhancement of dislocation density. The value increases from 2.2 1011/m2 in as-cast sample to 8.9 1013/m2 in the 3 T treated one. Besides, stacking faults and deformation twins with 3, 4, 6 atomic planes can also be seen. The results demonstrate that high pulsed electromagnetic field is an efficient and economical approach to acquire a specific microstructure and, meanwhile, keep the original shape of sample. & 2013 Elsevier B.V. All rights reserved.
Keywords: Composite materials Microstructure
1. Introduction In the past decades, many attentions have been paid to the combination of electromagnetic field with new processing of advanced materials, together with the emergence of a novel concept as EPM (Electromagnetic Processing of Materials). In most cases, both the force and heat effect of electromagnetic fields were employed to influence the hyperthermia fabricating process of materials [1], the grain refining during solidification [2], phase transformation [3] and sometimes the heat treatment [4]. But the effect of high electromagnetic field on the structural evolution of solid metal/alloy at room temperature has scarcely reported. Based on the theoretical analysis, the impact effect of Lorentz force induced by high electromagnetic field is big enough to result in the deformation of metal. Hopefully a high electromagnetic field will take a positive role in the structural evolution of some solid material. In this paper a prepared Al2O3 particles reinforced aluminum matrix composite was subjected to a specific impact by high pulsed electromagnetic field (HPEMF) at different magnetic induced intensity (B). The structural evolution and mechanisms have been revealed and further discussed in detail. The Al2O3 particles reinforced aluminum matrix composites exhibit the characteristics of nanometer particles and uniform distribution of particles in matrix, which has focused the attentions of some researchers. Due to a group of available reports the
n Corresponding author at: Jiangsu University, School of Materials Science & Engineering, 301 Xurfu Road, Zhenjiang 212013, PR China. Tel.: þ86 51 188 789 850. E-mail address: [email protected] (G. Li).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.02.089
comparison will be easily conducted among microstructures resulted from different treatment process.
2. Materials and processing In situ 1 vol% Al2O3 particles reinforced aluminum matrix composites were fabricated in advance via direct melt reaction method [5]. The as-cast composites were processed into flakes with the size of 20 mm 20 mm 2 mm. They were placed and fixed onto a refractory block with several slots. A refractory with little susceptibility would not interfere with the load-carrying of samples. Fig. 1 showed the sample status and relationship with the HPEMF, where P was the magnetic pressure and J the induced current. Then the samples were subjected to the impact treatment by HPEMF, aiming to search for a new approach to acquire a specific microstructure to improve the properties of materials, meanwhile, not to affect the original shape of samples. The levels of B were set as 1 T, 2 T and 3 T and the imposed pulse number was 30 in total. The processing parameters have been illustrated in Fig. 2, where IO and UO meant the output current and voltage of electric controller. High-resolution transmission electron microscopy (HRTEM) investigations were carried out with a JEOL-2100F TEM. The values of B were tested preciously by a LZ-610H Tesla meter.
3. Results and discussions Fig. 3 shows the particle distribution and dislocation morphology of as-cast and HPEMF-treated samples at different B values. The
G. Li et al. / Materials Letters 99 (2013) 50–53
in situ Al2O3 particles distribute uniformly in the matrix. The average sizes of them are in the range of 30–50 nm. In the as-cast sample there are only a few dislocations, some of which exist along or around the particles (Fig. 3a). But high density and various dislocations can be seen in the three HPEMF-treated samples at different B. Just as we know, the generation of high density dislocations is often the result of tensile or compressed deformation [6]. When B¼ 1 T and P¼0.79 MPa, the generated dislocation exhibits banded shape and 3.8 1012/m2 density that is 16.3 times in comparison to the value of 2.2 1011/m2 in as-cast sample(Fig. 3b). At the condition of B¼2 T and P¼3.17 MPa, the dislocation density further adds up to 6.7 1013/m2. When the dislocation moves forward rapidly and comes across an alumina
F
J
particle, it will circle around the particle and its shape will change from banded to hooped one, together with the increase of dislocation density (Fig. 3c). When B¼3 T and P¼7.14 MPa, the dislocation density increase continuously till to 8.9 1013/m2 (Fig. 3d). If compared to the value at 2 T the amplification is not apparent as before. On this occasion the increment of dislocation are attributed to the deformation induced by the Lorentz force effect of HPEMF. The magnetic pressure P can be expressed and calculated by Eq. (1) [7], where m0 is the magnetic conductivity of composites as 1.26 10 6 H/m. P¼
B2
ð1Þ
m0
So P equals to 7.14 MPa corresponding to B is 3 T. In comparison to the 8.35 MPa yield strength of Al2O3p/Al composites (a tested value) the samples processed by HPEMF are subjected to an elastic deformation. If B is larger than 3.23 T the P will be larger than 8.35 MPa the elastic deformation will convert to a plastic one and the sample cannot keep its original shape. In each cycle the peak impact lasts for about 1.1 s. Upon receiving the strong and instantaneous impact in a form of compression stress the sample will deform elastically, then recovers to its original state in a form of tension stress when the impact passes. The repeating 30 cycles with alternant compression and tension stress are attributed to the elastic deformation and dislocation behavior. Fig. 4 demonstrates the HRTEM diagrams of the above four samples in one grain. The incident direction is ½1 1 0. In the ascast sample the atoms are in an aligned array. No apparent disordered atomic arrays can be observed. In Fig. 4b there are two areas displaying the disordered atomic arrays and testifying the elastic deformation in composites. In Fig. 4c, besides one area showing the disordered atomic array, there is an apparent directional change of atomic array about 1451. In Fig. 4d the stacking fault (SF) and deforming twin (DT) can be found. In fcc metals, because of energy considerations, dislocations with strengths larger than unity are generally unstable and tend to dissociate into two or more dislocations of lower strength. SFs and DTs can
(a) B
51
B
S A M P L E
Refractory Block Fig. 1. The sample status and relationship with the electromagnetic field.
1.1 s
……
1T Io=4A
Magnetic induced intensity, T
UO=1.0V
30 cycles in total Time, s
(One cycle takes 2.8s) …… 2T
1.1 s Io=4A UO=1.2V
30 cycles in total Time, s
(One cycle takes 3.5s) 3T
……
1.1 s
Io=4.1A UO=1.5V (One cycle takes 4.3s) Fig. 2. The magnetic parameters of HPEMF at different B.
Time, s
.2
52
G. Li et al. / Materials Letters 99 (2013) 50–53
Fig. 3. TEM photograph of as-cast sample (a) and those treated at different B; (b) 1T; (c) 2T; (d) 3T.
Fig. 4. HRTEM diagram of samples at different states (a) as-cast; (b) 1T; (c) 2T; (d) 3T.
G. Li et al. / Materials Letters 99 (2013) 50–53
be formed from the dissociation of either screw dislocations [8]. SFs formed by two 301 Shockley partials dissociated from end-on 01 screw dislocations were frequently observed in the severe plastic deformed alloy [9]. While in the HPEMF-treated composites, SFs induced by the pulsed impact has never been reported in previous literatures. It is deduced that, in some sense, the effect of HPEMF is similar to the severe plastic deformation. For the formation mechanism of DTs, they are attributed to the dynamic overlapping of several SFs of dissociated dislocations on adjacent slip planes. The twin can grow thicker from three (DT1), four (DT3) to six atomic planes (DT2 in Fig. 4d) by adding more SFs on either side of the twin [10]. Furthermore, as indicated in Fig. 4d, high density dislocations are present around the twin boundary. Assuming that the electron beam and dislocation line are parallel to ½1 1 0 incident direction, these dislocations are determined to be on the ð1 1 1Þ plane with Burgers vectors of 1/2[1 0 1]. They are believed to be associated with the twin formation process. These results suggest that partial dislocation emission in fcc metals could also become a deformation mechanism in HPEMF treated aluminum.
4. Conclusions Upon receiving the magnetic pulsed impact by HPEMF the Al2O3p/Al composites will deform elastically due to the magnetic Lorentz force. The dislocation density increases with the increase of B in the range of 1–3 T. In the 3 T treated sample stacking faults
53
and deformation twins with 3, 4, 6 atomic planes can be seen. In summary, HPEMF is an efficient and economical approach to acquire a specific microstructure similar to severe plastic deformation, but still can, meanwhile, keep the original shape of sample.
Acknowledgments This work was financially supported by the NSFC (51001054, 51174099, 51174098), Natural Science Foundation of Jiangsu Province (BK2011533), open funds of SKLMMC of SJTU(mmckf12-06), Key lab of Cryogenics, TIPC-CAS (CRYO201106) and National Science Foundation for post-doctors and Jiangsu’s (20100471382, 1001023C).
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]
Li GR, Zhao YT. J Uni Sci Technol Beijing 2007;14:460–3. Li X, Ren ZM. J Mater Proc Tech 2008;195:125–34. Wang B, Yang YS, Sun ML. Trans Nonferrous Met Soc China 2012;20:1685–90. Akhbarizadeh A, Amini K, Javadpour S. Mater Des 2012;41:114–23. Li GR, Wang HM. Trans Nonferrous Met Soc China 2010;18:577–83. Li GR, Zhang XY. Adv Mater Res 2011;284–286:2280–3. Liu MP, Roven HJ, Yu YD. Int J Mater Res 2007;98:184–90. Yamakov V, Wolf D, Phillpot SR. Acta Mater 2002;50:5005–20. Zhou SJ, Perston DL. Science 1998;279:1525–7. Patel A, Das S, Prasad BK. Mater Sci Eng A 2011;530:225–32.