Anisotropic elastic moduli and internal friction of graphene nanoplatelets/silicon nitride composites
Introduction
Graphene nanoplatelets (GNPs) were recently used as fillers for Si3N4 ceramic composites with the aim to obtain advanced materials with enhanced fracture toughness, or electric and thermal conductivity [1], [2], [3], [4], [5]. Due to the superior elastic properties of graphene (the in-plane Young’s modulus equal to 1.1 TPa [10]), the presence of such particles in the ceramic matrix can be also expected to have some significant impact on the macroscopic elastic moduli of the composite, especially if they are arranged along some preferred directions and form, thus, a spatially anisotropic microstructure. In this paper, we study the case of silicon nitride ceramics with 3 wt.% of GNPs prepared by spark plasma sintering (SPS), where the preferred orientation of the platelets is induced by uniaxial stress applied during the sintering process [3], [4], [5]. The knowledge of elastic constants of such material is important not only with respect to its possible mechanical applications, but, as we show in this paper, enables also a deeper insight into micromechanics of the composite. In addition, the determination of elastic constants reported here is complemented by analysis of the anisotropic internal friction in the examined material, which is a parameter never discussed for graphene/ceramic composites so far. While the mechanical, micromechanical and vibrational properties of graphene/polymer nanocomposites have been studied numerous times and from numerous points of view (e.g. [6], [7], [8]), similar analysis for graphene/ceramic composites is still lacking; this paper aims to present one of the possible approaches how this gap can be filled.
Section snippets
Examined material
The examined composite was prepared by SPS (Dr. Sinter, SPS-510CE, Japan) from the mixture of α-Si3N4 powders (plus sintering additives: 2 wt.% Al2O3 and 5 wt.% Y2O3) and 3 wt.% of GNPs. The details on mixing, homogenization and SPS conditions were reported in [4]. The prepared specimen was cylindrical, with 20 mm in diameter and 2.7 mm in thickness. The density of this material was 3.18 g cm−3, which equals to 99% of the theoretical one (calculated using values of 3.23 g cm−3 for Si3N4 and 2.2 g cm−3 for
Experimental determination of elastic constants
From the SPS specimen, two rectangular parallelepipeds of dimensions approximately 4 × 3 × 2 mm3 were prepared, oriented such that the shortest edge was always perpendicular to the preferred orientation of the platelets, i.e. that the largest face was always parallel to the expected isotropic plane. These two samples (denoted hereafter Sample 1 and Sample 2) were used for the determination of elastic coefficients by means of resonant ultrasound spectroscopy (RUS, [13], [14]). In particular, the
Discussion of elastic anisotropy
First of all, let us point out that the anisotropy induced by 3 wt.% of GNPs is surprisingly strong: the difference between the longitudinal moduli along the platelets and perpendicular to them is approximately 30% of . The overall character of the anisotropy can be more easily seen from the directional dependence of the Young’s modulus shown in Fig. 2. The Young’s modulus in any given direction n can be calculated from the coefficients aswhere is a matrix
Analysis of anisotropic internal friction
Besides the determination of the elastic coefficients, the obtained RUS spectrum also enables the estimation of anisotropy of internal friction in the examined material. If the damping is small, the internal friction coefficients can be directly extracted from the widths of the resonant peaks (more precisely from the values of FWHM/f, where FWHM denotes the full width at the half maximum of the peak and f is the resonant frequency) by using the perturbation theory [21], [22]. Since the RUS
Conclusions
This paper illustrates that the anisotropy of elastic moduli and of internal friction in the graphene/ceramic composites can be reliably analyzed by ultrasonic methods, in this case particularly by resonant ultrasound spectroscopy complemented by pulse-echo measurements. In summary, it can be concluded that the presence of just 3 wt.% of GNPs leads to significant anisotropization of the Young’s elastic modulus and the internal friction of SPSed Si3N4, while the anisotropy of the shear modulus is
Acknowledgements
This work was supported by Czech Science Foundation (Project No.GA 101/09/0702), Academy of Sciences of the Czech Republic (Project No. M100761203) and the Spanish Government (Project No. MAT2009-09600). C. Ramirez thanks the financial support of the JAE (CSIC).
References (23)
- et al.
Fracture toughness and toughening mechanisms in graphene platelet reinforced Si3N4 composites
Scripta Mater
(2012) - et al.
Anisotropic thermal conductivity of silicon nitride ceramics containing carbon nanostructures
J Eur Ceram Soc
(2012) - et al.
Electrical conductivity maps in graphene nanoplatelet/silicon nitride composites using conducting scanning force microscopy
Carbon
(2011) - et al.
Graphene nanoplatelet/silicon nitride composites with high electrical conductivity
Carbon
(2012) - et al.
The mechanics of graphene nanocomposites: a review
Compos Sci Technol
(2012) Micromechanical analysis of nanocomposites using 3D voxel based material model
Compos Sci Technol
(2012)- et al.
Vibrations of carbon nanotubes and their composites: a review
Compos Sci Technol
(2007) - et al.
Low temperature elastic properties of chemically reduced and CVD-grown graphene thin films
Diam Rel Mater
(2010) - et al.
Resonant ultrasound spectroscopic techniques for measurement of the elastic moduli of solids
Physica B
(1993) - et al.
Application of ultrasonic methods to determine elastic anisotropy of polycrystalline copper processed by equal-channel angular pressing
Acta Mater
(2010)
On approximate symmetries of the elastic properties and elliptic orthotropy
Int J Eng Sci
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