Welcome to contribute
Carbon nanotubes (CNTs) reinforced aluminum (Al) composites are considered to be ideal lightweight structural materials with excellent mechanical properties. Over the past few decades, carbon nanotubes have shown extraordinary strengthening effects on aluminum matrices, and various strengthening mechanisms have been proposed. Unfortunately, the strength enhancement of CNT/Al composites is usually accompanied by considerable ductility loss due to the low dislocation storage capacity of ultrafine grains (UFG) and the pinning effect of CNT on dislocations, which limits their Engineering applications.
In August 2022, the top composite journal "Composites Part B" published Northeastern University and Metal Institute enhanced the strength-plasticity aspects of carbon nanotube/Al-Cu-Mg composites by introducing layered structures and grain modifications. research work. The paper is titled "Enhanced strength–ductility synergy of carbon nanotube/Al–Cu–Mg composites via introducing laminate structure and grain modification."
In the article, the laminated carbon nanotube (CNT)/Al-Cu-Mg composite is composed of alternating ductile layers (coarse-grained or ultra-fine-grained Al) without CNTs and brittle layers (ultra-fine grains) rich in CNTs. Prepared by powder metallurgy method. The results show that the strength-ductility of the composites is significantly improved compared to homogeneous composites. The mechanical incompatibility between different layers during tensile deformation generates a large number of geometrically necessary dislocations (GNDs) between the ductile and brittle layers, which suppresses strain localization and thus improves the strength-plasticity. Compared with the laminated composite with coarse-grained Al as the ductile layer, the strength of the laminated composite with ultra-fine-grained Al as the ductile layer further increased by 14%, while the elongation of and remained unchanged. . This is because ultra-fine grains of the ductile layer instead of coarse grains can lead to higher strength and better coordination with the brittle layer.
As-received CNTs with an average diameter of 10 nm and a length of more than 5 μm (Fig. 1(a)) were provided by Tsinghua University. The composition of atomized 2009Al alloy powder with an average diameter of 10 μm (Fig. 1(b)) is Al-4.5 wt% Cu-1.5 wt% Mg. The ground 2009Al alloy (Fig. 1(c)) and 3 vol% CNT/2009Al composite (Fig. 1(d)) powders were obtained by ball milling in an ultrafine pulverizer operating at a rotation speed of 250 rpm and a ball-to-powder ratio. Maintain a 15:1 ratio for 10 hours in a pure argon atmosphere. The inset of Figure 1(e) shows that CNTs can be individually inserted into Al powder after grinding.
Figure 1. SEM images of different powders: (a) as-received CNT, (b) atomized 2009Al, (c) ground 2009Al, and (d) ground 3 vol% CNT/2009Al (inset shows CNTs in Composite powder ground under TEM).
Figure 2 Schematic diagram of the preparation route of laminated composite materials.
Atomized and ground 2009Al were used to obtain ductile layers (DLs), respectively, while 3 vol% CNT/2009Al powder was used to obtain brittle layers (BLs) of laminated composites. The schematic diagram of the preparation route of laminated composite materials is shown in Figure 2. First, DL and BL powders are alternately laid into a cylindrical mold, and then cold pressed at 813 K and hot pressed under vacuum to form a blank with a layer thickness ratio of 1:2. This thickness ratio results in a laminated composite with a nominal CNT concentration of 2 vol%. The cylindrical material was taken out from the billet perpendicular to the hot pressing direction and then hot extruded into bars at 723 K with an extrusion ratio of 16:1. The hot extruded bars were further hot rolled along the extrusion direction at 753 K at a rate of 15% per pass to reduce the direction by 75%. Finally, the hot-rolled composites were solution treated at 773 K for 2 h, then quenched in water and naturally aged for more than 96 h.
Figure 3. Layer structure and grains of (a) (c) CG DL-BL, (b) (d) UFG DL-BL; (e) (f) Crystal grains and CNT distribution in BL.
Figure 4 TEM and HRTEM images of the laminated composite boundary between DL and BL in laminated composites: (a) and (b) CG DL-BL, (c) UFG DL-BL, and (d-f) BF , HAADF and CG DL-BL element mapping.The microstructure of the DL-BL boundary of the
laminated composite is shown in Figure 4. The TEM and HRTEM images are shown in Figure 4(a–f), further confirming that no hole defects are observed at the BL-DL boundary and the two layers are tightly bonded. The elemental mapping shown in Figure 4(f) shows that no elemental segregation of Cu or Mg was detected at the BL-DL boundary. All of this suggests that BL and DL are relatively independent and well integrated.
Figure 5 HRTEM images of the structure around the CNT-Al interface in BLs. The HRTEM image of the structure around the CNT-Al interface in
laminated composite BL is shown in Figure 5. This shows that the wall structure of the CNT is well retained and the CNT-Al interface is well bonded (Figure 5(a) and (b)), indicating that subsequent hot rolling did not further damage the structure of the CNT. In addition, some nanoscale Al4C3 particles were formed in the region attached on or near some CNTs (Fig. 5(c) and (d)). It is well known that a certain amount of interfacial reaction can increase interfacial bonding, which is beneficial to improving strengthening efficiency.
Figure 6. (a) Tensile curves of laminated composites and corresponding DL and BL materials, (b) Tensile curves of uniform and laminated CNT/2009Al with nominal 2 vol% CNT, (c) CNT/ Strength-ductility comparison of Al composites made by HEBM.
Figure 6(c) shows the strength-ductility reported in the literature. It can be seen that all composites exhibit a trade-off between strength and ductility, i.e., high strength is accompanied by low ductility. However, laminated composites exhibit relatively higher strength-ductility compared to reported homogeneous composites.
Figure 7. (a) Partially enlarged tensile curve and (b) strain hardening of homogeneous and laminated composites. (c)-(f) Ex-situ TEM images showing the dislocation evolution corresponding to the tip drop on the stretch curve at point “c-f”. (g1)-(g3) Schematic illustration of dislocation evolution during deformation. The first stage: elastic deformation of ; the second stage: elastic-plastic deformation; the third stage: plastic deformation of .
According to the above analysis, the tensile deformation of laminated composite materials can be divided into three stages. During the elastic phase, DLs and BLs deform independently (Fig. 7(g1)). In the elastoplastic stage, plastic deformation preferentially occurs in soft DLs, while BLs are still in the elastic deformation stage (Fig. 7(g2)). During the plastic stage, both BLs and DLs undergo plastic deformation (Fig. 7(g3)). However, since the plastic strain in DLs is larger than that in BLs, strain gradient occurs not only in DLs but also in BLs near the interface. These strain gradients become larger as they continue to deform, forming more GNDs and causing to backstress to harden. At different stages, DLs and BLs undergo different deformations. As a result, back stresses and GNDs are generated to mitigate deformation incompatibilities at the interface. It has been reported that laminated structures can provide a large number of zone boundaries that separate zones of different stiffness. Therefore, the existence of back stress between DLs and BLs increases the deformation ability of BLs, which is also the reason for the increase in the elongation of the composite.
Figure 8. Typical OM and SEM images of longitudinal and cross sections of two different laminated composites: (a) (b) (c) CG DL-BL. (d) (e) (f) UFG DL-BL.
Figure 9. Comparison of experimental and calculated tensile properties of heterogeneous composites: (a) YS, (b) UTS, and (c) SDP.
Figure 10 Microstructure of UFG DL-BL laminated composites with increasing tensile strain at different tensile stages. (a) and (b) no deformation, (c) elastic stage and (d) (f) plastic stage with different pre-stretching stages.
Figure 10 shows the TEM images of UFG DL-BL at different stretching stages. Overall, the dislocation accumulation trend of UFG DL-BL under different strains was similar to that of CG DL-BL (Fig. 7). In addition to the large number of dislocations in DLs, there are also obvious dislocations in BLs (Fig. 10(d)–(f)), which indicates that the CNT/2009Al grains in BLs can also plastically deform and sustain strain hardening under tension. .This provides direct evidence that dislocations in cause hardening and contribute to the observed high strain hardening capacity.
In this work, CNT/2009Al composites with layered structure were prepared by combining PM with hot rolling. The main conclusions are as follows:
(1) CNT/2009Al laminated composites consisting of a CNT-free ductile layer and a CNT-rich brittle layer were successfully fabricated. BLs and DLs are tightly combined without defects, which is conducive to giving full play to the performance of each layer of the entire sample.
(2) By building a laminated structure, they successfully achieved an excellent combination of strength and ductility in composite materials. The increased dislocation storage capacity and back stress hardening effect caused by GNDs are the main reasons for the excellent ductility of laminated composites.
(3) The coordinated deformation ability between DLs and BLs is improved by appropriately refining the grain size of BLs. As a result, UFG DL-BL achieved simultaneous improvements in strength and elongation compared with uniform and CG DL-BL. This provides new ideas for the design of high-strength and toughness composite materials.
Original article
P.Y. Li, In Composites Part B 243, p. 110178. DOI: 10.1016/j.compositesb.2022.110178.
Original link
https://www.sciencedirect.com/science/article/pii/S1359836822005534
focuses on the creation and sharing of knowledge in the field of composite materials mechanics . It is one of the most influential technical exchange platforms in the field of domestic composite materials. It updates cutting-edge technologies in the direction of composite materials as soon as possible, and publishes cutting-edge information, simulation cases, and technical methods. , code plug-ins have helped improve the professional literacy and professional skills of countless students, and are deeply loved by the majority of students and young science and technology workers. "Focus on the frontier and lead the future", the Composite Materials Mechanics Public Platform looks forward to your attention!
| Original works may not be reproduced without permission|
Official account homepage reply to the following numbers to obtain the corresponding information
【01】: Historical article【02】: Submission guidelines【03】: Video materials
【04】: Material library【05】 ：Technical training 【06】: Project cooperation
【07】: Business cooperation 【08】: Article reprint 【09】: Join us
【10】: Contact us 【11】: Communication group 【12】: Opinions and suggestions
The microstructure of the DL-BL boundary of thelaminated composite is shown in Figure 4. The TEM and HRTEM images are shown in Figure 4(a–f), further confirming that no hole defects are observed at the BL-DL boundary and the two layers are tightly bonded. The elemental mapping shown in Figure 4(f) shows that no elemental segregation of Cu or Mg was detected at the BL-DL boundary. All of this suggests that BL and DL are relatively independent and well integrated.
Figure 5 HRTEM images of the structure around the CNT-Al interface in BLs. The HRTEM image of the structure around the CNT-Al interface in
laminated composite BL is shown in Figure 5. This shows that the wall structure of the CNT is well retained and the CNT-Al interface is well bonded (Figure 5(a) and (b)), indicating that subsequent hot rolling did not further damage the structure of the CNT. In addition, some nanoscale Al4C3 particles were formed in the region attached on or near some CNTs (Fig. 5(c) and (d)). It is well known that a certain amount of interfacial reaction can increase interfacial bonding, which is beneficial to improving strengthening efficiency.
Figure 6. (a) Tensile curves of laminated composites and corresponding DL and BL materials, (b) Tensile curves of uniform and laminated CNT/2009Al with nominal 2 vol% CNT, (c) CNT/ Strength-ductility comparison of Al composites made by HEBM.
Figure 6(c) shows the strength-ductility reported in the literature. It can be seen that all composites exhibit a trade-off between strength and ductility, i.e., high strength is accompanied by low ductility. However, laminated composites exhibit relatively higher strength-ductility compared to reported homogeneous composites.
Figure 7. (a) Partially enlarged tensile curve and (b) strain hardening of homogeneous and laminated composites. (c)-(f) Ex-situ TEM images showing the dislocation evolution corresponding to the tip drop on the stretch curve at point “c-f”. (g1)-(g3) Schematic illustration of dislocation evolution during deformation. The first stage: elastic deformation of ; the second stage: elastic-plastic deformation; the third stage: plastic deformation of .
According to the above analysis, the tensile deformation of laminated composite materials can be divided into three stages. During the elastic phase, DLs and BLs deform independently (Fig. 7(g1)). In the elastoplastic stage, plastic deformation preferentially occurs in soft DLs, while BLs are still in the elastic deformation stage (Fig. 7(g2)). During the plastic stage, both BLs and DLs undergo plastic deformation (Fig. 7(g3)). However, since the plastic strain in DLs is larger than that in BLs, strain gradient occurs not only in DLs but also in BLs near the interface. These strain gradients become larger as they continue to deform, forming more GNDs and causing to backstress to harden. At different stages, DLs and BLs undergo different deformations. As a result, back stresses and GNDs are generated to mitigate deformation incompatibilities at the interface. It has been reported that laminated structures can provide a large number of zone boundaries that separate zones of different stiffness. Therefore, the existence of back stress between DLs and BLs increases the deformation ability of BLs, which is also the reason for the increase in the elongation of the composite.
Figure 8. Typical OM and SEM images of longitudinal and cross sections of two different laminated composites: (a) (b) (c) CG DL-BL. (d) (e) (f) UFG DL-BL.
Figure 9. Comparison of experimental and calculated tensile properties of heterogeneous composites: (a) YS, (b) UTS, and (c) SDP.
Figure 10 Microstructure of UFG DL-BL laminated composites with increasing tensile strain at different tensile stages. (a) and (b) no deformation, (c) elastic stage and (d) (f) plastic stage with different pre-stretching stages.
Figure 10 shows the TEM images of UFG DL-BL at different stretching stages. Overall, the dislocation accumulation trend of UFG DL-BL under different strains was similar to that of CG DL-BL (Fig. 7). In addition to the large number of dislocations in DLs, there are also obvious dislocations in BLs (Fig. 10(d)–(f)), which indicates that the CNT/2009Al grains in BLs can also plastically deform and sustain strain hardening under tension. .This provides direct evidence that dislocations in cause hardening and contribute to the observed high strain hardening capacity.
In this work, CNT/2009Al composites with layered structure were prepared by combining PM with hot rolling. The main conclusions are as follows:
(1) CNT/2009Al laminated composites consisting of a CNT-free ductile layer and a CNT-rich brittle layer were successfully fabricated. BLs and DLs are tightly combined without defects, which is conducive to giving full play to the performance of each layer of the entire sample.
(2) By building a laminated structure, they successfully achieved an excellent combination of strength and ductility in composite materials. The increased dislocation storage capacity and back stress hardening effect caused by GNDs are the main reasons for the excellent ductility of laminated composites.
(3) The coordinated deformation ability between DLs and BLs is improved by appropriately refining the grain size of BLs. As a result, UFG DL-BL achieved simultaneous improvements in strength and elongation compared with uniform and CG DL-BL. This provides new ideas for the design of high-strength and toughness composite materials.
Original article
P.Y. Li, In Composites Part B 243, p. 110178. DOI: 10.1016/j.compositesb.2022.110178.
Original link
https://www.sciencedirect.com/science/article/pii/S1359836822005534
focuses on the creation and sharing of knowledge in the field of composite materials mechanics . It is one of the most influential technical exchange platforms in the field of domestic composite materials. It updates cutting-edge technologies in the direction of composite materials as soon as possible, and publishes cutting-edge information, simulation cases, and technical methods. , code plug-ins have helped improve the professional literacy and professional skills of countless students, and are deeply loved by the majority of students and young science and technology workers. "Focus on the frontier and lead the future", the Composite Materials Mechanics Public Platform looks forward to your attention!
| Original works may not be reproduced without permission|
Official account homepage reply to the following numbers to obtain the corresponding information
【01】: Historical article【02】: Submission guidelines【03】: Video materials
【04】: Material library【05】 ：Technical training 【06】: Project cooperation
【07】: Business cooperation 【08】: Article reprint 【09】: Join us
【10】: Contact us 【11】: Communication group 【12】: Opinions and suggestions
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-