Interface structure regulation and thermal expansion coefficient of tungsten-coated diamond/copper composites

Tungsten (W) coating with thickness of 300 nm was deposited on the diamond surface by magnetron sputtering, and the influence of heat treatment parameters on the phase transformation of the W coating on the diamond surface was studied. The W-coated diamond particles after heat treatment were then prepared into Cu matrix composites by pressure infiltration. The influence of the phase evolution of the W coatings on the thermal expansion coefficient of the Diamond/Cu composite was studied systematically. The results show that the W coatings on the diamond particles begin to react with the diamond to form W₂C at 900℃. As the heat treatment temperature increases, the C atoms in the diamond particles gradually react with W and W₂C to form WC phase. Noteworthy, the C atoms on the diamond surface tend to graphite at high temperature of 1200℃. The evolution of the tungsten-coating phase significantly influences the interface bonding of the diamond/Cu composites, and subsequently impacting its coefficient of thermal expansion. As the W phase gradually transforms into the corresponding carbide phases (W₂C, WC), the interface gap in the composite diminishes, leading to an increase in the effective volume fraction of diamond. Consequently, the coefficient of thermal expansion exhibits a fluctuating trend with initial decrease followed by an increase, consistent with variations predicted by Turner and Kerner models. In cases where the interface structure of the composites is Diamond/WC/W₂C/Cu, its coefficient of thermal expansion can be as low as 6.35×10⁻⁶ K⁻¹ (50℃). Good interface bonding and the low thermal expansion coefficient and high elastic modulus of the interface layer play a critical role in enhancing load transfer efficiency and reducing the coefficient of thermal expansion for the composite. This work provides a theoretical basis for optimizing the coefficient of thermal expansion of diamond/copper composite and the selection of the interface carbide layer.