Papers by Author: Yan Cui

Abstract: For obtaining materials with high thermal conductivities and suitable thermal expansion coefficient for thermal management applications, diamond/Al composites were fabricated by the low-cost pressureless metal infiltration. The resulting composites exhibited thermal conductivities as high as 518.7 W/m•K and thermal expansion coefficient as low as 4.61×10-6/K friendly matching with semiconductors materials like Si or GaAs. The diamond particles were not only well embedded, but also uniformly distributed in the metallic matrix along with SEM observations of the composites. Fractograph of the composites illustrated that aluminum matrix fracture was the dominant fracture mechanism and the stepped breakage of diamond particles indicated strong interfacial bonding between diamond and the Al matrix. The Si skeleton with coralline morphology in the interface between diamond and the matrix were found to play a role of bridge in the interfacial structure and result in distinctive interfacial bonding. Also a little content of Al4C3 were realized to have positive effect on the improved thermal conductivities for promoting interfacial bonding between aluminum and diamond. In addition, the excellent mechanical behavior of the composite was illustrated. The results shows a superior Young’s modulus of 286 GPa compared with traditional thermal management materials and relatively high bending strength of 306MPa.

Abstract: The chemical element and its valence at the fracture surface of SiCp/Al2O3-Al composites synthesized by oxidative infiltration of Al melt were analyzed quantitatively using X-ray photoelectron spectrometer(XPS), the percentage content of various phase at fracture surface was determined accordingly. Additionally, the volume fraction of different phase in the composites was meassured by optical metallographic examination of the three-dimensional section. And then, by the comparison of phase content between fracture surface and section of the composites, the preference for the crack penetrating various phases of the composites was identified ,which in turn micro-fracture mechanisms of the composites were revealed quantitatively. It is proved that SiC particle size has a critical influence on the percent content of co-continuous Al2O3 and Al phases, as well as the micro-fracture mechanisms of this kind of composites. Based on the analysis of micro-fracture mechanisms, the moderate size (about 10μm) of SiC particulate would be beneficial to the mechanical properties of composites, the tested results of mechanical properties under room and elevated temperature verified the hypothesis.

Abstract: High volume fraction (63vol.%) SiCp/Al composite for electronic packaging fabricated by pressureless infiltration was characterized by microscopy, physical and mechanical tests. Microscopy observations and XRD analysis indicated that the composite appeared to be free of porosity and macroscopically homogeneous, SiC-Al interface was atomic bonding interface with low thermal resistivity and electrical resistivity, no interfacial reaction products was detected. Examination of the fracture surfaces of the composites revealed that the cracks passed through the SiC particles and Al matrix, no debonding of SiC-Al interface was observed. The fracture mode indicated that the bonding between SiC-Al was sufficient strong. The properties of the composite were noted for its ultrahigh thermal conductivity of 235W/m·K and specific modulus (79.9×105m), low coefficient of thermal expansion (7.2×10-6/K) and density of 2.99g/cm3. The advantages of the composite over traditional materials used as the electronic packages for aerospace applications were analyzed.