| The increase of integration level has led to an inevitable heat emission of electrical devices. Higher thermal dissipation properties of thermal management materials (TMMs) were demanded for making electronic products more high-powered and reliable. Kovar alloy, WCu alloy and SiC/Al are typical third generation TMMs, but thermal conductivity of each of them is lower than 220 Wm-1K-1. Since traditional TMM could no longer meet the requirement of ever-developing modern thermal dissipation technology, composite of materials has become an irresistible trend. The latest high thermal conductivity composite has overcame deficiencies of traditional TMMs, and forth generation TMMs, represented by diamond particle enhanced metal-matrix composite, has shown a great thermo-physical property. Diamond/Al composite plays an irreplaceable role in the field of lightweight.In this study, in order to seek the optimum parameter of diamond surface coating, surface metallization treatment of diamond was performed through preparing a layer of Ti/Cr by vacuum stowly vapor deposition or a layer of W by chemical vapor deposition (CVD) method. The influence of liquid Al on the wettability of coated diamond film was also studied. Diamond(x)/Al composite were fabricated using vacuum pressure infiltration system, so that the regularities of how infiltration temperature and holding time affect the micro structure and performance of the composite could be summarized. Thermal conductivity, coefficient of thermal expansion (CTE) and mechanical property of coated diamond film were compared and analyzed with these properties of uncoated diamond film. Theoretical thermal conductivities of three different kinds of clad layers were calculated using interface thermal resistance model.The results indicate that, the improvement of inter facial adhesion be twee n Al-matrix and reinforcement can be achieved by choosing the right cladding material and plating pr℃ess. Otherwise, the introduction of plating could destroy the integrity between matrix and reinforcement and this might introduce malignant interface, which would cause the decrease of composite thermo- physical property. Depositing a layer of Ti using vacuum slowly vapor deposition method, and critical parameters were 780℃,100 min. The thermal conductivity of Diamond(Ti)/Al composite will reach 517 Wm-1K-1 after soaking for 30 min at 960℃. The thermal conductivity is much higher than that of composite prepared by uncoated diamond particles. Cr clad layer was deposited at a higher temperature of 810℃ for 120 min, and the thickness of Cr clad layer is approximately 1.3μm P and Trans-crystalline fractures were found in fracture morphology of the composite when pressure infiltration was performed at 960℃, and interface selective was improved. Measured value of thermal conductivity of Diamond(Cr)/Al composite was 269 Wm-1K-1, which did not indicate a good thermal conductivity property. Combined with the analysis of EDS data, diffusion of Cr on diamond surface was evident, but the high solubility has decreased the thermal conductivity of Al-matrix. SEM images reveal that Al-matrix in Diamond(Cr)/Al composite no longer presents a good continuity, and dimple is not obvious. Besides, there exists a large amount of vacancies, which virtually increased the interrace thermal resistance. W was deposited on the surface of diamond by CVD method at 900℃ for 90 min. A uniform layer of WC was synthesized on the surface of diamond, and the thickness is about 1 μm. Analysis results show that interrace bond within Diamond(W)/Al composite can be improved by increasing the infiltrating temperature. Trans-crystalline fracture was found in fracture morphology of the composite when infiltrating temperature was 1150℃, and thermal conductivity of the composite was 143 Wm-1K-1. Comparing the measured value with theoretical model, interface thermal resistance of Diamond(W)/Al composited was largely increased, which is contrary to the excellent interface bond. Observation of the fracture morphology of the composite indicates that, solubility of W in Al-matrix is rather high, and bonding strength between clad layer and diamond particle is not ideal. Depositing W by CVD method at high temperature may cause burning on diamond surface and vacancies in the reinforcement has broken the integrity of diamond particles, which lead to the decrease of the intrinsic thermal conductivity of diamond. Hence, right kind of cladding material and proper clad layer thickness helps increase the thermal conductivity of composite while performing modification through surface treatment. In contrast, improper choice may introduce extra thermal resistance and malignant interface, which may cause a harmful influence. |
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