Short communicationPreparation and thermophysical properties of directional SiC/Cu–Si composite via spontaneous infiltration
Introduction
The development of electronic devices with higher calculating speeds and smaller compact size leads to an increased heat production per unit. In order to meet thermal dissipation requirements for electronic devices, heat sink materials with high thermal conductivity (TC) and tailored coefficients of thermal expansion (CTE) matching with those of semiconductor substrates (4–7×10−6 K−1) are desired [1], [2], [3], [4].
As a promising heat sink material, SiC reinforced copper matrix (SiC/Cu) composite has attracted considerable attentions due to its excellent thermophysical properties and good mechanical properties [5], [6], [7]. Generally, particulate SiC reinforcements are used to produce these composites [8], [9]. In order to match the CTE of the SiC/Cu composite with the substrates, high volume fractions of SiC particles are needed to incorporate into Cu-matrix due to the large CTE of Cu (αCu=16.47×10−6 K−1). However, the TC of the composite is decreased inevitably because of the relatively lower TC of SiC [10]. Recently, many studies confirmed that the phase continuity of ceramic reinforcement can significantly improve the thermophysical properties of metal–matrix composites [11]. Li et al. [12] reported that the TC and CTE of porous SiC ceramic reinforced Al-matrix composite were 70.2 W m−1 K−1 higher and 1.4×10−6 K−1 lower than those of SiC particles reinforced Al-matrix composites with similar SiC content respectively. Furthermore, compared with the isotropic porous ceramic as reinforcement, directional porous ceramic reinforced metal–matrix composites are expected to exhibit superior thermophysical properties. For instance, Roy et al. [13] reported the fabrication of directional Al2O3/Al composites by using freeze-casted Al2O3 ceramics with lamellar structure as reinforcement, and found that even lower CTE value parallel to the freezing direction can be obtained. However, the fabrication of directional SiC/Cu composite has rarely been reported.
The spontaneous infiltration of molten metals into porous ceramic preforms has been an attractive processing route for producing ceramic–metal composites owing to its simplicity, low cost and the near-net-shapes with complex parts [3], [7]. In this paper, directional SiC/Cu–Si composite was successfully fabricated via spontaneous infiltration of Cu-24 at%Si alloy into a directional porous SiC ceramic produced by a high temperature recrystallization process. The microstructure of the resultant composite was characterized, and its thermophysical properties along different directions were investigated. The Cu-24 at%Si alloy was chosen here for two reasons. First, the nonreactivity between the alloy and SiC can prevent the continuous structure of directional porous SiC ceramic from damage. Second, the good wettability between them was crucial for the realization of a spontaneous infiltration process [14].
Section snippets
Experimental
The starting materials used in present work were commercial grade β-SiC powder (d50=100 μm, 98.5%purity), Cu powder (d50=70 μm, 99.7% purity) and Si powder (d50=70 μm, 99.9% purity). Directional porous SiC ceramic with a porosity of 52% was prepared by the high temperature recrystallization process, as reported in our previous study [15]. Briefly, proper amounts of SiC powder was added into a graphite crucible and compacted by vibration. Then, the crucible was sintered at 2200 °C for 2 h in vacuum
Results and discussion
The fracture surfaces of the directional porous SiC ceramics normal to the axial and radial directions are exhibited in Fig. 2(a) and (b), respectively. As can be seen, the columnar SiC crystals show a fibrous structure which is parallel to the axial direction. The directional and tubular pores that are intercommunicating result in the formation of the long conducting channels, which is similar to the cellular structure of woods [16]. The formation mechanism of aligned pores can be ascribed to
Conclusions
In conclusion, using directional porous SiC ceramic prepared by high temperature recrystallization as reinforcement, directional SiC/Cu–Si composite was successfully prepared by a spontaneous infiltration process. The initial anisotropic microstructure of porous SiC ceramic could be retained after infiltration. Consequently, the prepared SiC/Cu–Si composite with directional microstructure exhibits significant thermophysical anisotropy, with both higher TC and lower CTE in the axial direction.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (No. 51172177), the Key (Key grant) Project of Chinese Ministry of Education (No. 313046) and the Program for New Century Excellent Talents in University (NCET-12–0454).
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