The evolutionary process and intermetallic compounds of Cu/Al couples during isothermal heating at a constant bonding temperature of 550°C were investigated in this paper. The interfacial morphologies and microstructures were examined by optical microscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, and X-ray diffraction. The results suggest that bonding is not achieved between Cu and Al at 550°C in 10 min due to undamaged oxide films. Upon increasing the bonding time from 15 to 25 min, however, metallurgical bonding is obtained in these samples, and the thickness of the reactive zone varies with holding time. In the interfacial region, the final microstructure consists of Cu₉Al₄, CuAl, CuAl₂, and α-Al + CuAl₂. Furthermore, these results provide new insights into the mechanism of the interfacial reaction between Cu and Al. Microhardness measurements show that the chemical composition exerts a significant influence on the mechanical properties of Cu/Al couples.

The coefficients of thermal expansion (CTE) and thermal conductivity (TC) are important for heat sink applications, as they can minimize stress between heat sink substrates and chips and prevent failure from thermal accumulation in electronics. We investigated the interface behavior and manufacturing of diamond/Cu composites and found that they have much lower TCs than copper due to their low densities. Most defects, such as cavities, form around diamond particles, substantially decreasing the high TC of diamond reinforcements. However, the measurement results for the Cu-coated diamond/Cu composites are unsatisfactory because the nanosized copper layer on the diamond surface grew and spheroidized at elevated sintering temperatures. Realizing ideal interfacial bonding between a copper matrix and diamond particles is difficult. The TC of the 40 vol.% Ti-coated diamond/Cu composite is 475.01 W m⁻¹ K⁻¹, much higher than that of diamond/Cu and Cu-coated diamond/Cu composites under equivalent manufacturing conditions. The minimally grown titanium layer retained its nanosized and was consistent with the sintering temperature. Depositing a nanosized titanium layer on a diamond surface will strengthen interfacial bonding through interface reactions among the copper matrix, nanosized titanium layer and diamond particles, reducing the interfacial thermal resistance and exploiting the high TC of diamond particles, even if defects from powder metallurgy remain. These results provide an important experimental and theoretical basis for manufacturing diamond/Cu composites for heat sink applications.

Carbon fiber is mainly distributed in the shape of short fibers and continuous fiber bundles as the reinforcing phase in metal matrix composites, and it is seldom studied as braided rope shaped to reinforce the matrix. For this paper, the pretreatment and the surface metallization of the carbon fiber braided rope were studied. Besides, the casting experiments of aluminum-based carbon fiber braided rope composites were performed without external pressure. XPS analysis shows that the surface of the carbon fiber braided rope treated with ultrasonic degumming contains many hydrophilic oxygen-containing functional groups C-OH, C=O, COOH, etc., which can effectively improve the wettability between the carbon fiber braided rope and the aluminum matrix. SEM, EDS, and XRD were used to analyze the micromorphology and structure of the copper plating on the surface of carbon fiber braided ropes obtained from different pH plating solutions. When pH is 12, a continuous, uniform, and dense layer was formed on the surface of carbon fiber braided ropes. In addition, copper coating can effectively inhibit the formation of Al₄C₃ brittle phase. Finally, the mechanical properties results indicated that the tensile strength of the carbon fiber bundle and carbon fiber rope reinforced composite materials were 69 MPa and 83 MPa, respectively, indicating that the reinforcing effect of the carbon fiber rope is better than that of the carbon fiber bundle.

Diamond/Cu composites are widely studied as a new generation of thermal management materials in the field of electronic packaging and heat sink materials. The surface modification of diamond can improve interfacial bonding between the diamond and Cu matrix. The Ti-coated diamond/Cu composites are prepared via an independently developed liquid-solid separation (LSS) technology. It is worth noting that there are obvious differences for the surface roughness between the diamond-{100} and -{111} face by AFM analysis, which may be related to the surface energy of different facets. In this work, the formation of titanium carbide (TiC) phase makes up the chemical incompatibility between the diamond and copper, and the thermal conductivities of 40 vol.% Ti-coated diamond/Cu composites can be improved to reach 457.22 W·m⁻¹·K⁻¹. The results estimated by the differential effective medium (DEM) model illustrate that the thermal conductivity for 40 vol.% Ti-coated diamond/Cu composites show a dramatic decline with increasing TiC layer thickness, giving a critical value of ~260 nm.