Unveiling the Semicoherent Interface with Definite Orientation

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Unveiling the semi-coherent interface with definite orientation relationships between reinforcements and matrix in novel Al3BC/Al composites Yongfeng Zhao, Zhao Qian, Xia Ma, Houwen Chen, Tong Gao, Yuying Wu, and Xiangfa Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b08913 • Publication Date (Web): 27 Sep 2016 Downloaded from http://pubs.acs.org on October 1, 2016

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ACS Applied Materials & Interfaces

Unveiling the semi-coherent interface with definite orientation relationships between reinforcements and matrix in novel Al3BC/Al composites Yongfeng Zhaoa, Zhao Qiana, *, Xia Maa, Houwen Chenb, Tong Gaoa, Yuying Wua, Xiangfa Liua, * a

Key Laboratory for Liquid–Solid Structural Evolution & Processing of Materials, Ministry of

Education, Shandong University, Jinan 250061, China b

College of Materials Science and Engineering, Chongqing University, Chongqing 400044,China

ABSTRACT High-strength lightweight Al-based composites are promising materials for a wide range of applications. To provide high performance, a strong bonding interface for effective load transfer from the matrix to the reinforcement is essential. In this work, the novel Al3BC reinforced Al composites have been in-situ fabricated through a liquid-solid reaction method and the bonding interface between Al3BC and Al matrix has been unveiled. The HRTEM characterizations on the Al3BC/Al interface verify it to be a semi-coherent bonding structure with definite orientation 1) ; 112 0 // 011 . Periodic arrays of geometrical relationships: (0001) // (11 misfit dislocations are also observed along the interface at each (0001) plane or every five (11 1) planes. This kind of interface between the reinforcement and the matrix is strong enough for effective load transfer, which would lead to the evidently improved strength and stiffness of the introduced new Al3BC/Al composites. KEYWORDS: Al3BC; Al composites; interface; orientation relationships; semi-coherent

1

ACS Paragon Plus Environment


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1 INTRODUCTION Particulate reinforced metal matrix composites (PRMMCs) are ideally suitable for many structural and functional applications due to their generally high specific strength，high stiffness, isotropic properties and relatively simple processing as compared with monolithic materials and conventional fiber-reinforced composites 1-4. The properties of PRMMCs are determined not only by the reinforcement particulate size 5, distribution 6, volume fraction

7

and the matrix property,

but also by the structure of the particulate/matrix interface 8-10. As a ligament between particulates and matrix, the interface plays critical roles in the mechanical, physical and chemical properties of composite materials. A strong bonding interface is required for effective load transfer from the matrix to the reinforcement, leading to improved strength and stiffness

9-10

. The interfacial

properties have also been found to determine the failure mode of the composites, where the failure initiated by interfacial debonding is likely to occur when the interface is weak

4, 11

. As a result,

investigations on the interface structure have been one of the most important topics of the processing of MMCs 9-15. Generally, classified by the interfacial cohesion, the bonding of MMCs interface can be divided into the following classifications: mechanical bonding, diffusion bonding, chemical bonding and coherent or semi-coherent bonding

10, 12

. The mechanical bonding arises from mechanical

inter-locking between the matrix and reinforcements

10

. The diffusion bonding arises from the

mutual diffusion between them. Chemical bonding that always occurs along with a chemical reaction at the interface and leads to the formation of reaction product layer, is the prime interfacial cohesion in the MMCs

10

, eg. Cf /Al

16-17

, SiC/Al

18-20

, B4C/Al

21-24

MMCs, etc. This

kind of interfacial reaction can decrease the interfacial energy of the metal/reinforcement interface 2


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and improve the adhesion through chemical bonding

10

. However, the interfaces with serious

reaction between the reinforcement and Al matrix, especially with the presence of brittle intermetallic phases, such as the formation of brittle Al4C3 in the Cf /Al

16

or SiC/Al

composites18-19, do not favor good mechanical properties. Thus, coating of the reinforcement or modification of the matrix composition is adopted to prevent the unwanted interfacial reaction and enhance the wetting of reinforcements

17, 20, 24

. Another significant kind of interfacial cohesion in

MMC is coherent or semi-coherent bonding which occurs when the atoms of the matrix and reinforcement are in direct contact and is accomplished by exchange of electrons

10, 23

. This type

of bonding can be metallic, ionic or covalent. An interface with metallic bonding is more ductile than other bonding, and is desirable in the MMCs. During these years, the in-situ fabrication method has got more attentions for the advantages of much cleaner and stronger interface as well as uniformly-distributed fine reinforcements 25. As the reinforcements are in-situ fabricated from the matrix, the interface between them is more likely to form a coherent or semi-coherent bonding structure. In recent years, aluminum boron-carbide phases (such as Al3BC3, Al8B4C7, AlB24C4, etc.) in the Al–B–C system have become the topics of several current investigations since the composites reinforced by them possess excellent properties such as low density, high strength and high hardness 26-28. Al3BC which was firstly described as phase X 29 with a hexagonal crystal lattice (a= 3.491(2) Å, c= 11.541(4) Å)

30-31

is another promising reinforcement owing to its low density

(2.83 g/cm3; close to that of Al), high hardness (14 GPa), excellent thermal stability (stable up to 1700 K under a high pressure of 1.6–4.8 GPa) 326 GPa)

33

32

, and remarkable stiffness (Young’s modulus =

. Table 1 and Fig. 1 show our Density functional theory calculations of Al3BC 3



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structure. The first in-situ Al3BC reinforced Al composites have successfully been fabricated through a liquid-solid reaction method in our recent work 34 and the Al3BC particulates distribute uniformly in the matrix, leading to a remarkable enhancement of mechanical properties. However， the deep investigations on the interface between Al3BC and Al are still not documented yet. In this work, the novel Al3BC/Al composites are in-situ fabricated and their microstructures together with the bonding interface structure between reinforcements and Al matrix are unveiled. The semi-coherent Al3BC/Al interface with definite orientation relationships and periodic misfit dislocations is characterized. Table. 1 Theoretical and experimental crystal symmetry as well as lattice constants of Al3BC.

Method

System

Space Group

a (Å)

c (Å)

c/a

Calc.

Hexagonal

P63 / mmc

3.500(4)

11.559(3)

3.302(3)

Expt. 30

Hexagonal

P63 / mmc

3.491(2)

11.541(4)

3.305(9)

Fig. 1 Equilibrium crystal structure of Al3BC after geometry optimization and relaxation calculation, which can be described as a closest packing of Al atoms with a layer sequence ABACBC with isolated boron atoms placed in all octahedral voids between layers A and C while isolated C atoms occupied half of the trigonal voids in the layers B.

2 METHODS The Al3BC reinforced Al or 6061 matrix composites containing 15% (all compositions quoted in this work are nominal values in wt.% unless otherwise stated) Al3BC particulates were in-situ 4


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fabricated through a liquid-solid reaction method and they were well consolidated by extrusion process. More details on the synthesis methods have been documented in our previous work 34. The phase compositions and microstructures of the composites were characterized utilizing X-ray diffraction (XRD, Rigaku D/max-rB) and field emission scanning electron microscope (FESEM, SU-70, Japan) equipped with an energy dispersive X-ray spectroscopy (EDS) detector. High resolution transmission electron microscope (HRTEM, ZEISS LIBRA200) equipped with electron energy loss spectroscopy (EELS) was also used to identify the crystal structure of Al3BC and its bonding interface with Al matrix. The size of Al3BC particles was estimated using the Image-pro Plus software. Digital Micrograph and Single Crystal software were used to analyze the HRTEM results. In this work, the state-of-the-art Density Functional Theory (DFT) calculations have been performed using the projector augmented wave (PAW) method, which is implemented in the Vienna Ab initio Simulation Package. The generalized gradient approximation (GGA) has been used throughout the work and the K-points mesh of 21×21×9 has been used for the crystal. The geometry optimization and relaxation has fully been done by minimizing the total energy with a conjugate gradient algorithm and also minimizing stresses on the unit cell without any symmetry constraint. A plane wave basis set has been employed with an energy cutoff of 520 eV to describe the electronic wave function. The PAW potentials with the valence states 2s22p1 for B, 2s22p2 for C and 3s23p1 for Al have been employed. To determine the atom positions in the HRTEM images, image simulations of the Al3BC crystal using the equilibrium crystal structure were performed by HREM software in a wide range of defocus and thickness permutations. The crystal lattice of Al3BC particulate is established utilizing the Crystal Maker software. 5



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The strengthening effects of Al3BC were also verified through the tensile test on extruded Al or 6061 matrix composites with Al3BC concentration of 15% (labeled as 15-Al and 15-6061). The Al3BC/6061 composites were solution treated at 530℃ for 1 hour and then aged at 175℃ for 8 hours. For comparison, the matrix alloys were also tested. The tensile test was conducted on ‘dog-bone’ type specimens (5mm in diameter and 25mm in original gauge length) using a CMT700 universal material test machine at ambient temperature. The extension rate is taken as 2 mm/min according to the ASTM E08 standard. In each case, four specimens were tested and the average values were reported. 3 RESULTS AND DISCUSSIONS

3.1 Microstructure of the Al3BC/Al composites The microstructures of Al3BC/Al composites with weight fraction of 15% have been detected firstly by means of FESEM and STEM (Fig. 2). As the low magnification microstructures in Fig. 2a-b shown, large amounts of submicron Al3BC particulates with polygonal morphology distribute uniformly along the extrusion direction in the matrix. Although the Al3BC particles in the composites distribute homogenously in a whole, there still exist some areas where have few reinforcements. High magnification image of the area with more Al3BC particulates in Fig. 2c indicates that the reinforcements distribute separately in the matrix. The inserted image of Al3BC on the bending fracture surface reveals it to be the polyhedral morphology. Moreover, the scanning transmission electron microscope (STEM) microstructures in Fig. 2d correspond well to the morphology of the particulate observed by FESEM. In order to estimate the size of the particles, Image-pro Plus software is utilized. The result in Fig. 2e reveals that Al3BC particles have an average diameter of 230nm. Fig.2 f demonstrates the EDS spectrum which verifies the existence 6


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of Al, B and C element, indicating the particulates to be Al3BC. This is further verified by the EELS patterns shown in Fig. 2(g-h).

Fig. 2 Microstructures of the extruded 15% Al3BC/Al composites and the composition analyses of Al3BC particulates: (a-b) Low magnification FESEM images of the sample showing the distribution of the reinforcements; (c) High magnification FESEM microstructure of the area with more reinforcements; the inset shows the Al3BC particulates on the bending fracture surface; (d) Scanning transmission electron microscope (STEM) microstructures; (e Diameter of the particles estimated by Image-pro Plus software; (f) The EDS spectrum of the Al3BC particulate; (g-h) The EELS patterns which verify the existence of boron and carbon elements.

For deeper understanding of the Al3BC structure in this work, thorough analysis has been done. 0 direction The HRTEM results of the Al3BC particulate with incident beam parallel to the 112 is first observed in Fig. 3a-c. The Al atoms stacking sequence of Al3BC can be clearly observed along this viewing direction, as displayed in Fig. 3a. In order to confirm the corresponding 7



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relationship between the atoms in Al3BC and the bright spots in the image, the HRTEM image simulations of the Al3BC crystal were performed by HREM software in a wide range of defocus and thickness permutations. Simulations reveal that there is one-to-one correspondence between the Al atomic columns and the bright spots in the image. The boron and carbon atoms in the crystal cannot be resolved in microscope because of their weak diffraction power

35-38

. More

detailed data of the simulation are supplied in the Supporting Information. The inset in Fig. 3a shows the simulated image which corresponds well with the observed HRTEM image. The bright spots can be described as Al atoms stacking with the sequence of ABACBC along the [0001] direction with a periodicity of 11.56 Å. Note that it’s very hard for us to distinguish the A position from the C position, because the spacing between the Al1-Al3 plane (A position) and the Al4-Al6 plane (C position) (Fig. 3c) is only about 1 Å, which has exceeded the resolution of the instrument. However, we can still identify the sequence to be ABACBC rather than ABAABA, because the spacing between Al3 and Al4 layers (1.76 Å) is much smaller than the diameter of the Al atom (2.86 Å), which determines the impossibility of ABAABA sequence. The stacking sequence of ABACBC is consistent with the crystal structure of Al3BC, which is clearly illustrated in Fig. 3c. 0 zone axis was also observed as is exhibited in Fig. Then the HRTEM image oriented to the 011 3d. The image also corresponds well to the simulated image inserted in Fig.3d and the projected lattice configuration of Al3BC in Fig. 3f. When we compare the relative fast Fourier transforms 0 zone axis (Fig. (FFT) pattern indexed as 112 0 zone axis (Fig. 3b) with that indexed as 011 3b), it is noted that all reflections in the 112 0 pattern appear, but the (000) reflections with = odd in the 011 0 pattern are absent. For structures of the P63/mmc space group, the {000} and } reflections with = odd are forbidden {hh2ℎ

37

. The appearance of the (000) forbidden

8


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1 0 pattern can be attributed to the double diffraction 37-38. For reflections with = odd in the 21 example, the combination of (11 00) and (1 101) can give rise to a (0001) reflection when the 0 patterns, the incident beam is parallel to the 112 0 zone axis. However, in the 011 1 0) and (2 111) cannot give rise to a (0001) reflection because the (2 111) combination of (21 reflection is forbidden.

Fig. 3 HRTEM characterization on the crystal structure of Al3BC particulates: (a) HRTEM images of Al3BC taken with the incident beam parallel to the 112 0 direction. The inset shows the simulated HRTEM image by HREM software; (b) Relative fast Fourier transforms of Al3BC in (a); (c) Projected lattice configuration of Al3BC to a (112 0) plane in a 3*3*1 supercell; (d) HRTEM images of Al3BC taken with the incident beam parallel to the 0 direction. The inset shows the simulated image by HREM software; (e) Relative fast Fourier transforms of 011 Al3BC in (d); (f) Projected lattice configuration of Al3BC to a (011 0) plane in a 2*2*1 supercell.

3.2 Semi-coherent bonding interface between Al3BC and Al matrix As mentioned above, the interface between reinforcements and matrix plays crucial roles in the 9



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mechanical, chemical as well as the physical properties of the composites; thus, the investigations on the interface structure are significant and essential. To verify the structure of the interface between Al3BC and Al in the composites, Al3BC particulate embedded in the Al matrix has been selected to be detected by HRTEM. A characteristic interface between Al3BC and Al matrix is displayed in Fig. 4(a-d). From the higher magnification HRTEM images and FFT patterns inserted in Fig. 4a, Al3BC (left) and the Al matrix (right) are indexed at their 011 0 and 1 12 zone axes, respectively. As the Al3BC is in-situ fabricated, the interface is straight, clean and free of other compounds. Fig. 4b demonstrates the Fourier-filtered atomic resolution image which shows much clearer characteristic of the interface. It is noted that a certain orientation relationships exist between the adjacent phases. The (0001) and (21 1 0)

1) and (220) planes, planes parallel to the (11

respectively. The collinear relationships of these planes’ diffraction spots shown in the compound FFT patterns getting from the interface (Fig. 4c) also indicate this result. In addition, from the patterns, it can be noted that (21 1 4)

plane also parallels approximately to the (311)

plane. This kind of orientation relationship can be expressed as follows: 1) ; 011 0 // 1 12 (0001) // (11

(1)

The calculated SAED patterns of Al3BC and Al by Single Crystal software displayed in Fig. 4d correspond well with the compound FFT results, which clearly illustrates the orientation relationships expressed in equation (1). Fig. 4(e-h) shows another characteristic interface between Al3BC and Al matrix, oriented to the 112 0 and [011] zone axes, respectively. It clearly shows that the (0001) plane is also parallel to the (11 1) plane. The compound FFT patterns and calculated SAED patterns in Fig. 10


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4(g-h) also indicate the parallel relationships between them. This kind of orientation relationship can be expressed as follows: 1) ; 112 0 // 011 (0001) // (11

(2)

Fig. 4 HRTEM analysis of the characteristic interface between Al3BC and Al matrix, oriented to the

0 // 1 12 zone axes (a-d) or the 112 0 // 011 zone axes (e-h): (a&e) HRTEM image of 011 Al3BC/Al interface and the inserted higher magnification images and related FFT patterns; (b&f) Fourier-filtered atomic resolution image of the interface. (c&g) Compound FFT patterns the interface, corresponding to the area in (b or f); (d&h) Calculated SAED of Al3BC (black dots) and Al (red dots) by Single Crystal software.

Stereographic projection can effectively demonstrate the three-dimensional orientation relationships of the crystal planes; thus, it is usually adopted to investigate the interface. Fig. 5(a-b) displays the stereographic projections of the main low index crystal planes of Al and Al3BC along 011 and 112 0 direction respectively with a Wulff net every 30°. According to the orientation relationship observed in Fig. 4, as expressed by equation (2), we overlap the 1) plane, and finally get the superimposed stereographic (0001) plane with the (11 projection patterns as shown in Fig. 5c. The compound stereographic projection shows the orientation relationships between Al3BC and Al clearly. It is noted that the (1 100) plane at 11



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1 1) plane at the [011] zone axis, which is not the [112 0] zone axis is also parallel to the (2 observed in Fig. 4 for the absence of (2 1 1) reflection. The orientation relationship expressed by equation (1) is also verified, that is to say, the orientation relationships expressed by equation (1) and (2) are actually the same. The Al3BC particulates observed in Fig. 4(a-d) and Fig. 4(e-h) have the same orientation relationships with Al matrix, indicating the universality of this kind of orientation relationships. From the superimposed stereographic projection patterns, it’s easy to find that the planes of both Al3BC and Al on the equator coincide with each other exactly. In addition to the parallel orientation relationships mentioned above, there also exist many other orientation relationships such as (21 1 0) // (110)

Al,

(1 21 0) // (1 01)

Al,

(101 0) // (121)Al. Actually, once the orientation relationship expressed by equation (2) is achieved, other orientation relationships would be achieved consequently. That is to say, the orientation relationships between Al3BC and Al can be absolutely expressed by equation (2). In conclusion, the interface between Al3BC and Al is a semi-coherent bonding with definite orientation relationships expressed by equation (2).

Fig. 5 Stereographic projection of the Al3BC and Al: (a) Stereographic projection of Al along 011 direction; (b) Stereographic projection of Al3BC along 112 0 direction; (c) Compound stereographic projection showing the orientation relationships between Al3BC and Al.

To deeper understand the semi-coherent Al3BC/Al interface, the higher magnification 12


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0 // [011]Al Fourier-filtered HRTEM images of the interface were observed along the 112 12]Al directions (Fig. 6b), respectively. It is noted that periodic (Fig. 6a) and 011 0 // [1 arrays of geometrical misfit dislocations （labeled by ⟘） are clearly observed along the interface 1 )Al, implying that the interface is formed in a at each (0001) or every five ( 11 semi-coherent manner. The near-periodic spacing of these extra misfit dislocations is about 1.16 nm, corresponding to the spacing of (0001) plane. In order to estimate the semi-coherency of the interface, the continuity of closed-packed (0001) and (11 1)Al planes were examined. The lattice mismatch between the two phases can be calculated by the following equation 39: =

!!!" !!!"

#$

=

%.'( ).*%

#$

).*%

= 21.9%

(3)

The mismatch vector -./ predicted from the Burgers circuit shown in the HRTEM micrograph is 0 '

1]Al. In the case where all the elastic strain has been released by misfit dislocations, the [11

spacing between misfit dislocations S can be calculated by the following equation 39: S=

./│ │3 4

%.'(

= %).*% = 10.68 Å

(4)

The calculated spacing between misfit dislocations of 10.68 Å is smaller than the average measured value of 11.6 Å, which indicates that only about 92% of the lattice mismatch is accommodated by misfit dislocations and there still remains some mismatch accommodated 1)Al plane as shown in Fig. partially by an in-plane elastic strain indicted by the distortion of (11 6(a-b). Thus, the (0001) and (11 1) planes join each other at a semi-coherent interface with a large mismatch of 21.9%, accommodated whereby both of the misfit dislocation and elastic strain. Fig. 6c shows the schematic of the atomic configuration of the Al3BC/Al interface, which clearly illustrates the semi-coherent interface with misfit dislocation at every (0001) plane or every five (11 1)Al planes. Compared with the other kinds of interface such as chemical 13



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bonding interface, the semi-coherent interface has much smaller interfacial energy, leading to much stronger bonding strength.

Fig. 6 Fourier-filtered HRTEM images of Al3BC/Al interface with higher magnification, indicating the formation of one dislocation in per Al3BC unit cell: (a-b) Al3BC/Al interface with the incident beam parallel to the 112 0 and 011 0 directions of Al3BC, respectively; (c) The atomic configuration of the interface between Al3BC and Al matrix，oriented to the 011 0 and 1 12 zone axes, respectively.

3.3 Strengthening effects of Al3BC particulates on the matrix alloys The strong interface between reinforcement and Al matrix is the precondition of effective load transfer, finally leading to improved strength and stiffness. In this work the semi-coherent interface between Al3BC and Al matrix can effectively transfer the mechanical load from the matrix to Al3BC, and the result has been verified by tensile test on the extruded Al3BC/6061 or Al composites after T6 heat treatment. Fig. 7 displays the stress-strain curves of Al3BC reinforced Al and 6061 composites containing 15% Al3BC, labeled as 15-Al and 15-6061, respectively. For comparison, the Al and 6061 alloy without Al3BC addition are also tested. The specific values of the tensile tests on the samples are summarized in Table. 2. Compared with that of the matrix alloys, the ultimate tensile strength σb, the yield strength σy as well as the elastic modulus of the composites are all improved significantly, which suggest the promising strengthening effects of

14


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Al3BC on the matrix. The average ultimate tensile strength (UTS) of Al3BC reinforced Al or 6061 composites with 15% Al3BC particulates are 323 MPa and 525 MPa, 368.1% and 87.5% higher than that of the matrix alloys, respectively. In addition, the elongation of the Al or 6061 based composites keep in receivable values of 14.5% and 5.0%, respectively. The elastic modulus of the Al3BC/6061 composites can even reach up to 103 GPa, which is also improved significantly. The insets show the fracture surface of 15-Al and 15-6061 tensile samples, respectively. For the 15-Al samples, large amount of distried circular dimples occur on the fracture surface, indicating a failure mechanism resulting from ductile void growth, coalescence and failure. This kind of fracture mechanism belongs to a ductile fractured mechanism, which is beneficial to getting a higher plasticity. For the 15-6061 samples, both the ductile and the brittle fractures happened during the tensile process. Dimples on the fracture surface indicate the ductile fracture mechanism, while the cleavage planes on the Mg2Si particles indicate the brittle fracture of this kind of particle. The cracks nucleate on the Mg2Si-Al interface and then propagate across the particle directly. One point need to be mentioned is that Al3BC particles are rarely observed on both of the fracture structures, i.e., very few debonding phenomena occur during the tensile process, indicating a strong bonding interface between Al3BC and Al matrix. The high strength and stiffness of the composites verifies the strong enhancing effects of the Al3BC particulates benefitting from the strong semi-coherent interface investigated in this work.

15



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Fig. 7 Tensile stress-strain curves of extruded Al3BC reinforced Al or 6061 composites after T6 heat treatment with 15% Al3BC, labeled as 15-Al, 15-6061, respectively. The insets show the fracture surface of the tensile samples.

Table. 2 Tensile results of Al3BC reinforced Al or 6061 composites and the matrix alloy.

σb/MPa

σy/MPa

Yield Ratio

Modulus/GPa

Elongation/%

Al

69

43

0.62

9

33.0

15-Al

353

265

0.75

54

14.5

6061

280

210

0.75

64

17.0

15-6061

525

451

0.86

103

5.0

4 CONCLUSIONS The novel Al-based composites with submicron Al3BC particles as reinforcements have been in-situ prepared through a liquid-solid reaction method. The Al3BC/Al interface is characterized to be formed in a semi-coherent manner with definite orientation relationships: (0001) // (11 1) ; 112 0 // 011 . Periodic arrays of geometrical misfit dislocations are also observed along the interface at every (0001) plane or every five (11 1) planes. This kind of interface bonding is strong enough for effective load transfer and finally leads to improved 16


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strength and stiffness, which has been verified by tensile test on the composites. The average UTS of Al3BC reinforced Al and 6061 composites with 15% Al3BC are 353 MPa and 525 MPa, 368.1% and 87.5% higher than that of the matrix alloys, respectively. ASSOCIATED CONTENT Supporting Information HRTEM Image simulations of the Al3BC crystal using the equilibrium crystal structure were performed by HREM software in a wide range of defocus and thickness permutations. More detailed data of the simulation is displayed in the supporting information. AUTHOR INFORMATION Corresponding Authors * Tel.: +86 531 88392006; fax: +86 531 88395414. E-mail: [email protected] (Xiangfa Liu)；[email protected] (Zhao Qian). Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This research was financially supported by the National Natural Science Foundation of China (No.51271101) and the National Basic Research Program of China (973 Program, No. 2012CB825702). REFERENCES (1) Mortensen A.; Llorca J. Metal Matrix Composites. Annu. Rev. Mater. Res. 2010, 40, 243-270. (2) Ibrahim I.A.; Mohamed F.A.; Lavernia E.J. Particulate Reinforced Metal Matrix Composites– a Review. J. Mater. Sci. 1991, 26, 1137-1156. 17



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Unveiling the Semicoherent Interface with Definite Orientation

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