Effect of Nanometer WC Coating on Thermal Conductivity of Diamond/6061 Composites

Diamond has poor interface tolerance with Al. To enhance interface bonding, in this study, tungsten carbide (WC) nanocoatings on the surface of diamond particles were prepared using sol-gel and in-situ reaction methods. WO3 sol-gel with two concentrations, 0.2 mol/L, and 0.5 mol/L, was, respectively, coated on diamond particles, then sintered at 1250 degrees C for 2 h to produce WC nanocoatings. The concentration of 0.2 mol/L WO3 sol-gel was not enough to cover the surface of the diamond completely, while 0.5 mol/L WO3 sol-gel could fully cover it. Moreover, WO3 was preferentially deposited on {100} planes of the diamond. WO3 converted to WC in-situ nanocoatings after sintering due to the in-situ reaction of WO3 and diamond. The diamond-reinforced Al composites with and without WC coating were fabricated by powder metallurgy. The diamond/Al composite without coating has a thermal conductivity of 584.7 W/mK, while the composite with a coating formed by 0.2 mol/L and 0.5 mol/L WO3 sol-gel showed thermal conductivities of 626.1 W/mK and 584.2 W/mK, respectively. The moderate thickness of nanocoatings formed by 0.2 mol/L WO3 sol-gel could enhance interface bonding, therefore improving thermal conductivity. The nanocoating produced by 0.5 mol/L WO3 sol-gel cracked during the fabrication of the composite, leading to Al12W formation and a decrease in thermal conductivity.