- Email: [email protected]
Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites
MAT ER IA LS CH A R A CTE RI Z A TI O N 8 9 ( 2 0 14 ) 1–6
Available online at www.sciencedirect.com
ScienceDirect www.elsevier.com/locate/matchar
Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites Q.Q. Zhang, G.Q. Wu⁎, Z. Huang, Y. Tao School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191, PR China
AR TIC LE D ATA
ABSTR ACT
Article history:
The interfacial microstructure of SiCp or YAl2p reinforced Mg–14Li–3Al matrix composites
Received 2 November 2013
was comparatively characterized by scanning electron microscopy and electron probe
Received in revised form
microanalysis. A nanoindentation combined with scanning electron microscopy technique
20 December 2013
was used to characterize the interfacial mechanical properties between the reinforcements
Accepted 20 December 2013
and matrix. The interfacial strength and failure behaviors for the composites were analyzed from the load–penetration curves and corresponding images. In situ tensile tests were used to observe the fracture and deformation processes with the aid of scanning electron
Keywords:
microscopy. The results show that both the chemical and mechanical compatibilities
Particulate reinforced composites
between the YAl2 particles and LA143 matrix are better than those between the SiC particles
Interfaces
and LA143 matrix. The interfacial breakage load for the SiC/LA143 composite is lower than
Failure behavior
that for the YAl2/LA143 composite because of the worse chemical and mechanical
Characterization
compatibilities between the ceramic particles and metal matrix. Interfacial breakage is
Nanoindentation
the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanism for the YAl2/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix. © 2013 Elsevier Inc. All rights reserved.
1. Introduction The reinforcement/matrix interface, such as chemical reaction and element diffusion formed during the preparation process by the interactions of the reinforcement and the matrix, plays a crucial role in determining the properties of particle reinforced metal matrix composites (PMMCs) [1–3]. Most properties of the PMMCs such as strength [4], ductility [5], toughness [6] and fracture mode [7–9] depend on the interfacial behavior. The improvement of mechanical and chemical compatibility between the reinforcements and metal matrix has been attracting wide attention [10–12]. In recent years, intermetallic reinforcements are introduced to the PMMC area, on the one hand for their high strength, high ⁎ Corresponding author. Tel./fax: +86 1082313240. E-mail address: [email protected] (G.Q. Wu). 1044-5803/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.matchar.2013.12.010
elastic modulus and low work hardening rate, and on the other hand for potential inter-diffusion ability between the intermetallic particles and metals, which will be beneficial to the compatibility between the reinforcements and matrix [13–16]. In general, the failure behaviors for PMMCs display several features, such as interfacial breakage, particle breakage and matrix fracture, and the interfacial breakage is the most common due to the weak interfacial bonding strength between the reinforcements and matrix. Although the crack initiation position and propagation path can be observed by in‐situ SEM/ TEM [16–18], the relationship between the failure behavior and interfacial properties of the composites is hard to describe. In this paper, a nanoindentation combined with scanning electron microscopy technique was proposed to characterize the
2
MAT ER IA LS CH A R A CTE RI ZA TI O N 8 9 ( 2 0 14 ) 1–6
Fig. 1 – Geometry and dimension of the tensile specimens for SEM in‐situ observation.
interfacial mechanical properties between the reinforcements and matrix for the intermetallic/matrix and ceramic/matrix composites, and the failure behaviors for the composites were analyzed from the load–penetration curves and corresponding SEM images. The interfacial microstructure of YAl2 or SiC reinforced Mg–14Li–3Al (LA143) matrix composites was observed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The relationships among the type of reinforcements, particle/matrix interfaces and failure behaviors for the composites were discussed.
2. Materials and Methods A YAl2 (~30 μm, elastic modulus E1 = 158 GPa) reinforced LA143 matrix composite and a SiC (~30 μm, elastic modulus E2 = 330 GPa) reinforced LA143 composite were prepared by stir-casting at a resistance furnace under a protective argon atmosphere. The LA143 alloys (elastic modulus E3 = 34.5G Pa) were used as the base matrix alloy. The samples were cut from the two composites in order to get fresh surfaces for characterization. After cutting, the samples were metallographically polished with a 0.5 μm Al2O3 slurry. Thereafter the specimens were gold coated for scanning electron microscopy (SEM;
Fig. 3 – Scanning electron microscopy back scattered images and EPMA concentration profiles for the (a) YAl2/LA143 and (b) SiC/LA143 interface zones.
JSM-3400) and electron probe microanalysis (EPMA). Line profile quantitative elemental analyses were carried out by EPMA across the interface zones. After being metallographically polished, another two samples were used for nanoindentation immediately to avoid
Fig. 2 – Typical optical micrographs of (a) YAl2 and (b) SiC reinforced LA143 matrix composites.
MAT ER IA LS CH A R A CTE RI Z A TI O N 8 9 ( 2 0 14 ) 1–6
surface oxidation. The samples were subjected to the high load nanoindentations tests. The tests involved the application of single indentation marks in the proximity of the particle/matrix interfaces, increasing the penetration up to 1.5 μm to generate cracks in the interfaces with the Berkovich pyramid corner towards the interfaces. From the load–penetration curve in the loading stage of the test, the interfacial breakage load can be determined. At the same time, the bearing ability of the composites can also be determined by the slope of the curve at different stages. Then, the failure behaviors for the composites were analyzed from the curves. In our tests, 16 out of 24 indented YAl2 particles and 13 out of 24 indented SiC particles were suitable for the indentation data analysis. In situ tensile tests of the composites were used to observe fracture and deformation processes by JSM-5800 scanning electron microscope (SEM). The geometry of in situ tensile specimens is shown in Fig. 1. A notch of 0.25 mm in width and 80 μm in root radius was cut perpendicular to the loading direction in the middle of specimen for SEM in situ observation using electrical discharge machining (EDM).
3. Results 3.1. Microstructure and Interface Characterization for the Composites The typical optical micrographs of YAl2 or SiC particle reinforced LA143 matrix composites are shown in Fig. 2. The
3
YAl2/LA143 composite consists of YAl2 intermetallic particles and a (β)-Li phase, as shown in Fig. 2a. The SiC/LA143 composite consists of SiC ceramic particles and a (β)-Li phase, as shown in Fig. 2b. Both the YAl2 and SiC particles distribute homogeneously in the matrix alloys. Scanning electron microscopy back scattered images (SEM-BS) for the YAl2/LA143 and SiC/LA143 interface zones are shown in Fig. 3. A diffusion zone has been observed in the vicinity of the YAl2/LA143 interface. EPMA analysis confirms the presence of yttrium and aluminum in the diffusion zone about approximately 10 μm away from the YAl2/LA143 interface (Fig. 3a). For the SiC/LA143 interface, a relatively narrow diffusion zone less than 5 μm is presented in the vicinity of the interface. EPMA analysis showed little silicon in this zone (Fig. 3b). Additionally there is a weak bonding area at the SiC/LA143 interface, while the YAl2 particle matches well with the LA143 matrix.
3.2. High Load Nanoindentation Tests for the Interfacial Strength Fig. 4 shows the SEM images of nanoindentation imprints made with 1.5 μm penetration at the YAl2/LA143 and SiC/ LA143 interfaces. At the early stage of the indentation test, the YAl2 particle can be compatible with the deformation of the LA143 matrix, as shown in Fig. 4a. As the load increases, the interfacial breakage is clearly shown (arrowed on Fig. 4b), and a crack initiated and propagated in the particle. However, the interfacial breakage is not extensive. The SEM image for the
Fig. 4 – SEM images of nanoindentation imprints made with 1.5 μm penetrations at the (a) YAl2/LA143 interface and (b) SiC/ LA143 interface.
4
MAT ER IA LS CH A R A CTE RI ZA TI O N 8 9 ( 2 0 14 ) 1–6
Fig. 5 – The load–penetration curves measured for the indentation with 1.5 μm penetrations at the YAl2/LA143 interfaces.
Fig. 7 – The load–penetration curves measured for the indentation with 1.5 μm penetrations at the SiC/LA143 interfaces.
SiC/LA143 interface is shown in Fig. 4c. It is shown that the SiC particle is hard to deform compatibly with the LA143 matrix. A large amount of the interface broke after the high load indentation test (arrowed on Fig. 4d). The load–penetration curves measured for the indentations on the YAl2/LA143 interfaces are shown in Fig. 5, as well as an indentation test made into the LA143 matrix shown for comparison purpose (Fig. 6). For the curves, when the loads increase up to 40–60 mN, there is a step for each of the load– penetration curves, showing a discontinuity in the deformation behaviors due to the breakage of the YAl2/LA143 interface. The load for the interfacial breakage here is considered to be located between 25 and 45 mN (subtracting the contribution of the LA143 matrix). The slopes of the load– penetration curves do not change after the interfacial breakages. Cracks initiate and propagate in the particles at the loads of 80–90 mN, which are shown to be local breakages on the particles. After then, the slopes of the curves decrease, which reveal that the bearing ability of the YAl2/LA143 composite decreases due to the particle breakages.
For the SiC/LA143 interfaces, the load–penetration curves measured for the indentations are shown in Fig. 7. Arc stages are shown in the load–penetration curves after the SiC/LA143 interfacial breakages, which indicate that consecutive breakages happen. The minimum load for the interfacial breakages here is considered to 15 mN (subtracting the contribution of the LA143 matrix), as the slopes of the curves firstly decrease at this time. As the loads increase to 50–60 mN, total interfacial breakages occur and the slopes of the load– penetration curves decrease to zero, which means that the bearing ability of the SiC/LA143 composite has been totally lost. These imply that interfacial breakage is the main failure behavior for the SiC/LA143 composite, while particle breakage is the main failure behavior for the YAl2/LA143 composite.
Fig. 6 – The nanoindentation imprints made for comparison at the vicinity of the interface. (a) SEM image, (b) the corresponding load–penetration curve used in Fig. 5.
3.3. In‐Situ SEM Observation for the Fracture Process The in situ observation of fracture process in the YAl2/LA143 composite by SEM is shown in Fig. 8 [19]. It can be seen that the micro-cracks mainly initiate in the matrix rather than in the interfaces (Fig. 8a), and the micro-cracks propagate in the matrix that is about 5 μm away from the interface (Fig. 8b). Two initiated cracks propagate to each other. There are two arc propagation routes for both cracks, and the route for the crack below propagates around the particle. These imply that YAl2 particles can be compatible with the deformation of the matrix due to their deformation, exhibiting a “soft” restriction to the matrix, and the YAl2 particles may resist the propagation of cracks in micro-scale during deformation of the composite. The fracture process for the SiC/LA143 composite by in situ SEM observation is shown in Fig. 9. As we can see, the micro-cracks mainly initiate in the interfaces rather than in the matrix or particles (arrowed in Fig. 9a). After deformation the micro-cracks propagate from the interface into the matrix (arrowed in Fig. 9b). The SiC particles can hardly be compatible with the deformation of the matrix, because the SiC particles are more brittle than the intermetallic particles. At the same time, some micro-cracks propagate into the particle, leading to the particle breakage, revealing that the SiC
MAT ER IA LS CH A R A CTE RI Z A TI O N 8 9 ( 2 0 14 ) 1–6
Fig. 8 – The propagation process of micro-cracks in the YAl2/ LA143 composite during the in‐situ observation [19]. (a) Crack initiation in the matrix, (b) crack propagation around the particles.
particles can hardly resist the propagation of cracks in micro-scale during deformation of the composite.
4. Discussion As we can see, the interface analysis by EPMA shows that diffusion easily happens between the YAl2 particle and LA143
5
matrix, while it is hard to happens between the SiC particle and LA143 matrix (Fig. 3). In addition, we can see that the YAl2 particle matches with the LA143 matrix better than the SiC particle. These phenomena reveal that the chemical compatibility between the YAl2 particle and LA143 matrix is better than that between the SiC particle and LA143 matrix. In the high load nanoindentation tests (Fig. 4), the YAl2 particle deforms compatibly with the LA143 matrix, while the SiC particle can hardly deform compatibly with the LA143 matrix. This indicates that the mechanical compatibility between the YAl2 particles and LA143 matrix is better than that between the SiC particles and LA143 matrix. The study in detail of the nanoindentation curves can help to identify possible inelastic phenomena occurring in those interfaces. The interfacial strength for the SiC/LA143 composite are lower than that for the YAl2/LA143 composite, which is probably related to the better chemical and mechanical compatibilities between the intermetallic particles and metal matrix (Figs. 5 and 7). As the previous studies showed, a diffusion interface can lead to a transition interface layer [20], where the stress can be released during the loading [19]. The local plastic deformation concentrates firstly at the junction of the particle and matrix, and the deformation here is always the maximum with increasing load in the SiC/LA143 composite without a transition interface layer. In this case, the interfacial breakage and particle debonding may occur easily (Fig. 4d). However, it is very different from the case with a transition interface layer which may be related to the better chemical and mechanical compatibilities between the intermetallic particles and metal matrix (Fig. 4b). Under such a circumstance, the interfacial breakage may be hard to occur, and the interfacial strength for the YAl2/LA143 interface is higher than that of the SiC/LA143 interface. The interfacial mechanical properties play a crucial role in the fracture behavior for the metal matrix composites [7–9]. In the SiC/LA143 composite with a lower interfacial strength, the interfacial breakage and particle debonding may occur easily during the deformation process (Fig. 4d). The results by in‐situ SEM observation show that the fracture process for the SiC/ LA143 composite is mainly determined by the interfacial
Fig. 9 – The propagation process of micro-cracks in the SiC/LA143 composite during the in‐situ observation. (a) Crack initiation in the interface, (b) crack propagation into the matrix.
6
MAT ER IA LS CH A R A CTE RI ZA TI O N 8 9 ( 2 0 14 ) 1–6
debonding (Fig. 9). However, it is very different from the YAl2/ LA143 composite with a higher interfacial strength (Fig. 4b). The YAl2 particles are “softer” as compared with ceramics. Under such a circumstance, the interfacial breakage may be hard to occur, and the failure of the intermetallic/matrix composite may be controlled by the particle breakage and ductile fracture in the matrix (Fig. 8). Both the results by in‐ situ observation are in agreement with the results derived by the high load nanoindentation tests.
[3]
[4]
[5]
[6]
5. Conclusions In summary, a nanoindentation combined with scanning electron microscopy technique was successfully used to characterize the failure behaviors for particle reinforced metal matrix composites, and the correlations between the interfaces and failure behaviors were discussed. The conclusions are as follows: (1) The YAl2/LA143 composite consists of YAl2 intermetallic particles and a (β)-Li phase, and the SiC/LA143 composite consists of SiC ceramic particles and a (β)-Li phase. Both the YAl2 and SiC particles distribute homogeneously in the matrix alloys. (2) The diffusion easily happens in the interface between the YAl2 intermetallic particles and LA143 matrix, while it is hard to happens between the SiC ceramic particles and LA143 matrix. Both the chemical and mechanical compatibilities between the YAl2 particles and LA143 matrix are better than those between the SiC particles and LA143 matrix. (3) The interfacial breakage load for the YAl2/LA143 composite is 25–45 mN (subtracting the contribution of the matrix), and the load for the SiC/LA143 composite is 15 mN. The interfacial breakage load for the SiC/LA143 composite is lower than the YAl2/LA143 composite because of the worse chemical and mechanical compatibilities between the ceramic particles and metal matrix. (4) Interfacial breakage is the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanisms for the YAl2/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix.
[7]
[8]
[9]
[10]
[11]
[12] [13]
[14]
[15]
[16]
[17]
Acknowledgments This paper is financially supported by the Natural Science Foundation of China (Grant No. 50901005) and the Fund of Aeronautics Science (Grant No. 2010ZF51068).
REFERENCES
[1] Evans RD, Boyd JD. Near-interface microstructure in a SiC/Al composite. Scr Mater 2003;49:59–63. [2] Schubert T, Ciupinski Ł, Zieliński W, Michalski A, Weisgarber T, Kieback B. Interfacial characterization of Cu/diamond
[18]
[19]
[20]
composites prepared by powder metallurgy for heat sink applications. Scr Mater 2008;58:263–6. Li YF, Liu P, Liu XD. Interface structure and formation mechanism of BN/intergranular amorphous phase in pressureless sintered Si3N4/BN composites. Scr Mater 2010;63:185–8. Chen SH, Jin PP, Schumacher G, Wanderka N. Microstructure and interface characterization of a cast Mg2B2O5 whisker reinforced AZ91D magnesium alloy composite. Compos Sci Technol 2010;70:123–9. Inoue J, Nambu S, Ishimoto Y, Koseki T. Fracture elongation of brittle/ductile multilayered steel composites with a strong interface. Scr Mater 2008;59:1055–8. Bartolome JF, Beltran JI, Gutierrez-Gonzalez CF, Pecharroman C, Munoz MC, Moya JS. Influence of ceramic–metal interface adhesion on crack growth resistance of ZrO2–Nb ceramic matrix composites. Acta Mater 2008;56:3358–66. Kennedy AR, Wyatt SM. Characterising particle–matrix interfacial bonding in particulate Al–TiC MMCs produced by different methods. Compos Part A 2001;32:555–9. Romanova VA, Balokhonov RR, Schmauder S. The influence of the reinforcing particle shape and interface strength on the fracture behavior of a metal matrix composite. Acta Mater 2009;57:97–107. Devinder Yadav, Ranjit Bauri. Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite. Mater Sci Eng A 2011;528:1326–33. Tham LM, Gupta M, Cheng L. Effect of limited matrix-reinforcement interfacial reaction on enhancing the mechanical properties of aluminium–silicon carbide composites. Acta Mater 2001;49:3243–53. Kudela Jr S, Wendrock H, Kudela S, Pawełek A, Pi˛atkowski A, Wetzig K. Fracture behavior of Mg–Li matrix composites. Int J Mater Res 2009;100:910–4. Trojanova Z, Drozd Z, Kudela S, Szaraz Z, Lukăc P. Strengthening in Mg–Li matrix composites. Compos Sci Technol 2007;67:1965–73. Laplanche G, Joulain A, Bonneville J, Schaller R, El Kabir T. Microstructures and mechanical properties of Al-base composite materials reinforced by Al–Cu–Fe particles. J Alloy Compd 2010;493:453–60. Abbasi Chianeha V, Madaah Hosseini HR, Nofar M. Microstructural features and mechanical properties of Al–Al3Ti composite fabricated by in-situ powder metallurgy route. J Alloy Compd 2009;473:127–32. Pour HA, Lieblich M, Lopez AJ, Rams J, Salehi MT, Shabestari SG. Assessment of tensile behaviour of an Al–Mg alloy composite reinforced with NiAl and oxidized NiAl powder particles helped by nanoindentation. Compos Part A 2007;38:2536–40. Wu GQ, Ling ZH, Zhang X, Wang SJ, Zhang T, Huang Z. Research on YAl2 intermetallics particles reinforced Mg–14Li–3Al matrix composites. J Alloys Compd 2010;507:137–41. Rosner H, Boucharat N, Markmann J, Padmanabhan KA, Wilde G. In situ transmission electron microscopic observations of deformation and fracture processes in nanocrystalline palladium and Pd90Au10. Mater Sci Eng A 2009;525:102–6. Son CY, Kim CK, Shin SY, Lee S, Parka I. In situ microfracture observation of Cu-based amorphous alloy matrix composites containing copper or brass particles. Mater Sci Eng A 2009;508:15–22. Yang X, Wu GQ, Sha W, Zhang QQ, Huang Z. Numerical study of the effects of reinforcement/matrix interphase on stress–strain behavior of YAl2 particle reinforced MgLiAl composites. Compos Part A 2012;43:363–9. Zhang QQ, Wu GQ, Niu LY, Huang Z, Tao Y. Effects of heat treatment on interface and mechanical properties of YAl2 reinforced Mg–14Li–3Al matrix composite. Mater Sci Eng A 2013;564:298–302.
Available online at www.sciencedirect.com
ScienceDirect www.elsevier.com/locate/matchar
Characterization of the correlation between the interfaces and failure behaviors for particle reinforced Mg–Li composites Q.Q. Zhang, G.Q. Wu⁎, Z. Huang, Y. Tao School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191, PR China
AR TIC LE D ATA
ABSTR ACT
Article history:
The interfacial microstructure of SiCp or YAl2p reinforced Mg–14Li–3Al matrix composites
Received 2 November 2013
was comparatively characterized by scanning electron microscopy and electron probe
Received in revised form
microanalysis. A nanoindentation combined with scanning electron microscopy technique
20 December 2013
was used to characterize the interfacial mechanical properties between the reinforcements
Accepted 20 December 2013
and matrix. The interfacial strength and failure behaviors for the composites were analyzed from the load–penetration curves and corresponding images. In situ tensile tests were used to observe the fracture and deformation processes with the aid of scanning electron
Keywords:
microscopy. The results show that both the chemical and mechanical compatibilities
Particulate reinforced composites
between the YAl2 particles and LA143 matrix are better than those between the SiC particles
Interfaces
and LA143 matrix. The interfacial breakage load for the SiC/LA143 composite is lower than
Failure behavior
that for the YAl2/LA143 composite because of the worse chemical and mechanical
Characterization
compatibilities between the ceramic particles and metal matrix. Interfacial breakage is
Nanoindentation
the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanism for the YAl2/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix. © 2013 Elsevier Inc. All rights reserved.
1. Introduction The reinforcement/matrix interface, such as chemical reaction and element diffusion formed during the preparation process by the interactions of the reinforcement and the matrix, plays a crucial role in determining the properties of particle reinforced metal matrix composites (PMMCs) [1–3]. Most properties of the PMMCs such as strength [4], ductility [5], toughness [6] and fracture mode [7–9] depend on the interfacial behavior. The improvement of mechanical and chemical compatibility between the reinforcements and metal matrix has been attracting wide attention [10–12]. In recent years, intermetallic reinforcements are introduced to the PMMC area, on the one hand for their high strength, high ⁎ Corresponding author. Tel./fax: +86 1082313240. E-mail address: [email protected] (G.Q. Wu). 1044-5803/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.matchar.2013.12.010
elastic modulus and low work hardening rate, and on the other hand for potential inter-diffusion ability between the intermetallic particles and metals, which will be beneficial to the compatibility between the reinforcements and matrix [13–16]. In general, the failure behaviors for PMMCs display several features, such as interfacial breakage, particle breakage and matrix fracture, and the interfacial breakage is the most common due to the weak interfacial bonding strength between the reinforcements and matrix. Although the crack initiation position and propagation path can be observed by in‐situ SEM/ TEM [16–18], the relationship between the failure behavior and interfacial properties of the composites is hard to describe. In this paper, a nanoindentation combined with scanning electron microscopy technique was proposed to characterize the
2
MAT ER IA LS CH A R A CTE RI ZA TI O N 8 9 ( 2 0 14 ) 1–6
Fig. 1 – Geometry and dimension of the tensile specimens for SEM in‐situ observation.
interfacial mechanical properties between the reinforcements and matrix for the intermetallic/matrix and ceramic/matrix composites, and the failure behaviors for the composites were analyzed from the load–penetration curves and corresponding SEM images. The interfacial microstructure of YAl2 or SiC reinforced Mg–14Li–3Al (LA143) matrix composites was observed by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The relationships among the type of reinforcements, particle/matrix interfaces and failure behaviors for the composites were discussed.
2. Materials and Methods A YAl2 (~30 μm, elastic modulus E1 = 158 GPa) reinforced LA143 matrix composite and a SiC (~30 μm, elastic modulus E2 = 330 GPa) reinforced LA143 composite were prepared by stir-casting at a resistance furnace under a protective argon atmosphere. The LA143 alloys (elastic modulus E3 = 34.5G Pa) were used as the base matrix alloy. The samples were cut from the two composites in order to get fresh surfaces for characterization. After cutting, the samples were metallographically polished with a 0.5 μm Al2O3 slurry. Thereafter the specimens were gold coated for scanning electron microscopy (SEM;
Fig. 3 – Scanning electron microscopy back scattered images and EPMA concentration profiles for the (a) YAl2/LA143 and (b) SiC/LA143 interface zones.
JSM-3400) and electron probe microanalysis (EPMA). Line profile quantitative elemental analyses were carried out by EPMA across the interface zones. After being metallographically polished, another two samples were used for nanoindentation immediately to avoid
Fig. 2 – Typical optical micrographs of (a) YAl2 and (b) SiC reinforced LA143 matrix composites.
MAT ER IA LS CH A R A CTE RI Z A TI O N 8 9 ( 2 0 14 ) 1–6
surface oxidation. The samples were subjected to the high load nanoindentations tests. The tests involved the application of single indentation marks in the proximity of the particle/matrix interfaces, increasing the penetration up to 1.5 μm to generate cracks in the interfaces with the Berkovich pyramid corner towards the interfaces. From the load–penetration curve in the loading stage of the test, the interfacial breakage load can be determined. At the same time, the bearing ability of the composites can also be determined by the slope of the curve at different stages. Then, the failure behaviors for the composites were analyzed from the curves. In our tests, 16 out of 24 indented YAl2 particles and 13 out of 24 indented SiC particles were suitable for the indentation data analysis. In situ tensile tests of the composites were used to observe fracture and deformation processes by JSM-5800 scanning electron microscope (SEM). The geometry of in situ tensile specimens is shown in Fig. 1. A notch of 0.25 mm in width and 80 μm in root radius was cut perpendicular to the loading direction in the middle of specimen for SEM in situ observation using electrical discharge machining (EDM).
3. Results 3.1. Microstructure and Interface Characterization for the Composites The typical optical micrographs of YAl2 or SiC particle reinforced LA143 matrix composites are shown in Fig. 2. The
3
YAl2/LA143 composite consists of YAl2 intermetallic particles and a (β)-Li phase, as shown in Fig. 2a. The SiC/LA143 composite consists of SiC ceramic particles and a (β)-Li phase, as shown in Fig. 2b. Both the YAl2 and SiC particles distribute homogeneously in the matrix alloys. Scanning electron microscopy back scattered images (SEM-BS) for the YAl2/LA143 and SiC/LA143 interface zones are shown in Fig. 3. A diffusion zone has been observed in the vicinity of the YAl2/LA143 interface. EPMA analysis confirms the presence of yttrium and aluminum in the diffusion zone about approximately 10 μm away from the YAl2/LA143 interface (Fig. 3a). For the SiC/LA143 interface, a relatively narrow diffusion zone less than 5 μm is presented in the vicinity of the interface. EPMA analysis showed little silicon in this zone (Fig. 3b). Additionally there is a weak bonding area at the SiC/LA143 interface, while the YAl2 particle matches well with the LA143 matrix.
3.2. High Load Nanoindentation Tests for the Interfacial Strength Fig. 4 shows the SEM images of nanoindentation imprints made with 1.5 μm penetration at the YAl2/LA143 and SiC/ LA143 interfaces. At the early stage of the indentation test, the YAl2 particle can be compatible with the deformation of the LA143 matrix, as shown in Fig. 4a. As the load increases, the interfacial breakage is clearly shown (arrowed on Fig. 4b), and a crack initiated and propagated in the particle. However, the interfacial breakage is not extensive. The SEM image for the
Fig. 4 – SEM images of nanoindentation imprints made with 1.5 μm penetrations at the (a) YAl2/LA143 interface and (b) SiC/ LA143 interface.
4
MAT ER IA LS CH A R A CTE RI ZA TI O N 8 9 ( 2 0 14 ) 1–6
Fig. 5 – The load–penetration curves measured for the indentation with 1.5 μm penetrations at the YAl2/LA143 interfaces.
Fig. 7 – The load–penetration curves measured for the indentation with 1.5 μm penetrations at the SiC/LA143 interfaces.
SiC/LA143 interface is shown in Fig. 4c. It is shown that the SiC particle is hard to deform compatibly with the LA143 matrix. A large amount of the interface broke after the high load indentation test (arrowed on Fig. 4d). The load–penetration curves measured for the indentations on the YAl2/LA143 interfaces are shown in Fig. 5, as well as an indentation test made into the LA143 matrix shown for comparison purpose (Fig. 6). For the curves, when the loads increase up to 40–60 mN, there is a step for each of the load– penetration curves, showing a discontinuity in the deformation behaviors due to the breakage of the YAl2/LA143 interface. The load for the interfacial breakage here is considered to be located between 25 and 45 mN (subtracting the contribution of the LA143 matrix). The slopes of the load– penetration curves do not change after the interfacial breakages. Cracks initiate and propagate in the particles at the loads of 80–90 mN, which are shown to be local breakages on the particles. After then, the slopes of the curves decrease, which reveal that the bearing ability of the YAl2/LA143 composite decreases due to the particle breakages.
For the SiC/LA143 interfaces, the load–penetration curves measured for the indentations are shown in Fig. 7. Arc stages are shown in the load–penetration curves after the SiC/LA143 interfacial breakages, which indicate that consecutive breakages happen. The minimum load for the interfacial breakages here is considered to 15 mN (subtracting the contribution of the LA143 matrix), as the slopes of the curves firstly decrease at this time. As the loads increase to 50–60 mN, total interfacial breakages occur and the slopes of the load– penetration curves decrease to zero, which means that the bearing ability of the SiC/LA143 composite has been totally lost. These imply that interfacial breakage is the main failure behavior for the SiC/LA143 composite, while particle breakage is the main failure behavior for the YAl2/LA143 composite.
Fig. 6 – The nanoindentation imprints made for comparison at the vicinity of the interface. (a) SEM image, (b) the corresponding load–penetration curve used in Fig. 5.
3.3. In‐Situ SEM Observation for the Fracture Process The in situ observation of fracture process in the YAl2/LA143 composite by SEM is shown in Fig. 8 [19]. It can be seen that the micro-cracks mainly initiate in the matrix rather than in the interfaces (Fig. 8a), and the micro-cracks propagate in the matrix that is about 5 μm away from the interface (Fig. 8b). Two initiated cracks propagate to each other. There are two arc propagation routes for both cracks, and the route for the crack below propagates around the particle. These imply that YAl2 particles can be compatible with the deformation of the matrix due to their deformation, exhibiting a “soft” restriction to the matrix, and the YAl2 particles may resist the propagation of cracks in micro-scale during deformation of the composite. The fracture process for the SiC/LA143 composite by in situ SEM observation is shown in Fig. 9. As we can see, the micro-cracks mainly initiate in the interfaces rather than in the matrix or particles (arrowed in Fig. 9a). After deformation the micro-cracks propagate from the interface into the matrix (arrowed in Fig. 9b). The SiC particles can hardly be compatible with the deformation of the matrix, because the SiC particles are more brittle than the intermetallic particles. At the same time, some micro-cracks propagate into the particle, leading to the particle breakage, revealing that the SiC
MAT ER IA LS CH A R A CTE RI Z A TI O N 8 9 ( 2 0 14 ) 1–6
Fig. 8 – The propagation process of micro-cracks in the YAl2/ LA143 composite during the in‐situ observation [19]. (a) Crack initiation in the matrix, (b) crack propagation around the particles.
particles can hardly resist the propagation of cracks in micro-scale during deformation of the composite.
4. Discussion As we can see, the interface analysis by EPMA shows that diffusion easily happens between the YAl2 particle and LA143
5
matrix, while it is hard to happens between the SiC particle and LA143 matrix (Fig. 3). In addition, we can see that the YAl2 particle matches with the LA143 matrix better than the SiC particle. These phenomena reveal that the chemical compatibility between the YAl2 particle and LA143 matrix is better than that between the SiC particle and LA143 matrix. In the high load nanoindentation tests (Fig. 4), the YAl2 particle deforms compatibly with the LA143 matrix, while the SiC particle can hardly deform compatibly with the LA143 matrix. This indicates that the mechanical compatibility between the YAl2 particles and LA143 matrix is better than that between the SiC particles and LA143 matrix. The study in detail of the nanoindentation curves can help to identify possible inelastic phenomena occurring in those interfaces. The interfacial strength for the SiC/LA143 composite are lower than that for the YAl2/LA143 composite, which is probably related to the better chemical and mechanical compatibilities between the intermetallic particles and metal matrix (Figs. 5 and 7). As the previous studies showed, a diffusion interface can lead to a transition interface layer [20], where the stress can be released during the loading [19]. The local plastic deformation concentrates firstly at the junction of the particle and matrix, and the deformation here is always the maximum with increasing load in the SiC/LA143 composite without a transition interface layer. In this case, the interfacial breakage and particle debonding may occur easily (Fig. 4d). However, it is very different from the case with a transition interface layer which may be related to the better chemical and mechanical compatibilities between the intermetallic particles and metal matrix (Fig. 4b). Under such a circumstance, the interfacial breakage may be hard to occur, and the interfacial strength for the YAl2/LA143 interface is higher than that of the SiC/LA143 interface. The interfacial mechanical properties play a crucial role in the fracture behavior for the metal matrix composites [7–9]. In the SiC/LA143 composite with a lower interfacial strength, the interfacial breakage and particle debonding may occur easily during the deformation process (Fig. 4d). The results by in‐situ SEM observation show that the fracture process for the SiC/ LA143 composite is mainly determined by the interfacial
Fig. 9 – The propagation process of micro-cracks in the SiC/LA143 composite during the in‐situ observation. (a) Crack initiation in the interface, (b) crack propagation into the matrix.
6
MAT ER IA LS CH A R A CTE RI ZA TI O N 8 9 ( 2 0 14 ) 1–6
debonding (Fig. 9). However, it is very different from the YAl2/ LA143 composite with a higher interfacial strength (Fig. 4b). The YAl2 particles are “softer” as compared with ceramics. Under such a circumstance, the interfacial breakage may be hard to occur, and the failure of the intermetallic/matrix composite may be controlled by the particle breakage and ductile fracture in the matrix (Fig. 8). Both the results by in‐ situ observation are in agreement with the results derived by the high load nanoindentation tests.
[3]
[4]
[5]
[6]
5. Conclusions In summary, a nanoindentation combined with scanning electron microscopy technique was successfully used to characterize the failure behaviors for particle reinforced metal matrix composites, and the correlations between the interfaces and failure behaviors were discussed. The conclusions are as follows: (1) The YAl2/LA143 composite consists of YAl2 intermetallic particles and a (β)-Li phase, and the SiC/LA143 composite consists of SiC ceramic particles and a (β)-Li phase. Both the YAl2 and SiC particles distribute homogeneously in the matrix alloys. (2) The diffusion easily happens in the interface between the YAl2 intermetallic particles and LA143 matrix, while it is hard to happens between the SiC ceramic particles and LA143 matrix. Both the chemical and mechanical compatibilities between the YAl2 particles and LA143 matrix are better than those between the SiC particles and LA143 matrix. (3) The interfacial breakage load for the YAl2/LA143 composite is 25–45 mN (subtracting the contribution of the matrix), and the load for the SiC/LA143 composite is 15 mN. The interfacial breakage load for the SiC/LA143 composite is lower than the YAl2/LA143 composite because of the worse chemical and mechanical compatibilities between the ceramic particles and metal matrix. (4) Interfacial breakage is the main failure mechanism for the SiC/LA143 composite, while the particle breakage and matrix crack are the main failure mechanisms for the YAl2/LA143 composite. These may be related to the stronger interfacial bonding between the intermetallic particles and metal matrix.
[7]
[8]
[9]
[10]
[11]
[12] [13]
[14]
[15]
[16]
[17]
Acknowledgments This paper is financially supported by the Natural Science Foundation of China (Grant No. 50901005) and the Fund of Aeronautics Science (Grant No. 2010ZF51068).
REFERENCES
[1] Evans RD, Boyd JD. Near-interface microstructure in a SiC/Al composite. Scr Mater 2003;49:59–63. [2] Schubert T, Ciupinski Ł, Zieliński W, Michalski A, Weisgarber T, Kieback B. Interfacial characterization of Cu/diamond
[18]
[19]
[20]
composites prepared by powder metallurgy for heat sink applications. Scr Mater 2008;58:263–6. Li YF, Liu P, Liu XD. Interface structure and formation mechanism of BN/intergranular amorphous phase in pressureless sintered Si3N4/BN composites. Scr Mater 2010;63:185–8. Chen SH, Jin PP, Schumacher G, Wanderka N. Microstructure and interface characterization of a cast Mg2B2O5 whisker reinforced AZ91D magnesium alloy composite. Compos Sci Technol 2010;70:123–9. Inoue J, Nambu S, Ishimoto Y, Koseki T. Fracture elongation of brittle/ductile multilayered steel composites with a strong interface. Scr Mater 2008;59:1055–8. Bartolome JF, Beltran JI, Gutierrez-Gonzalez CF, Pecharroman C, Munoz MC, Moya JS. Influence of ceramic–metal interface adhesion on crack growth resistance of ZrO2–Nb ceramic matrix composites. Acta Mater 2008;56:3358–66. Kennedy AR, Wyatt SM. Characterising particle–matrix interfacial bonding in particulate Al–TiC MMCs produced by different methods. Compos Part A 2001;32:555–9. Romanova VA, Balokhonov RR, Schmauder S. The influence of the reinforcing particle shape and interface strength on the fracture behavior of a metal matrix composite. Acta Mater 2009;57:97–107. Devinder Yadav, Ranjit Bauri. Processing, microstructure and mechanical properties of nickel particles embedded aluminium matrix composite. Mater Sci Eng A 2011;528:1326–33. Tham LM, Gupta M, Cheng L. Effect of limited matrix-reinforcement interfacial reaction on enhancing the mechanical properties of aluminium–silicon carbide composites. Acta Mater 2001;49:3243–53. Kudela Jr S, Wendrock H, Kudela S, Pawełek A, Pi˛atkowski A, Wetzig K. Fracture behavior of Mg–Li matrix composites. Int J Mater Res 2009;100:910–4. Trojanova Z, Drozd Z, Kudela S, Szaraz Z, Lukăc P. Strengthening in Mg–Li matrix composites. Compos Sci Technol 2007;67:1965–73. Laplanche G, Joulain A, Bonneville J, Schaller R, El Kabir T. Microstructures and mechanical properties of Al-base composite materials reinforced by Al–Cu–Fe particles. J Alloy Compd 2010;493:453–60. Abbasi Chianeha V, Madaah Hosseini HR, Nofar M. Microstructural features and mechanical properties of Al–Al3Ti composite fabricated by in-situ powder metallurgy route. J Alloy Compd 2009;473:127–32. Pour HA, Lieblich M, Lopez AJ, Rams J, Salehi MT, Shabestari SG. Assessment of tensile behaviour of an Al–Mg alloy composite reinforced with NiAl and oxidized NiAl powder particles helped by nanoindentation. Compos Part A 2007;38:2536–40. Wu GQ, Ling ZH, Zhang X, Wang SJ, Zhang T, Huang Z. Research on YAl2 intermetallics particles reinforced Mg–14Li–3Al matrix composites. J Alloys Compd 2010;507:137–41. Rosner H, Boucharat N, Markmann J, Padmanabhan KA, Wilde G. In situ transmission electron microscopic observations of deformation and fracture processes in nanocrystalline palladium and Pd90Au10. Mater Sci Eng A 2009;525:102–6. Son CY, Kim CK, Shin SY, Lee S, Parka I. In situ microfracture observation of Cu-based amorphous alloy matrix composites containing copper or brass particles. Mater Sci Eng A 2009;508:15–22. Yang X, Wu GQ, Sha W, Zhang QQ, Huang Z. Numerical study of the effects of reinforcement/matrix interphase on stress–strain behavior of YAl2 particle reinforced MgLiAl composites. Compos Part A 2012;43:363–9. Zhang QQ, Wu GQ, Niu LY, Huang Z, Tao Y. Effects of heat treatment on interface and mechanical properties of YAl2 reinforced Mg–14Li–3Al matrix composite. Mater Sci Eng A 2013;564:298–302.