Bonding of graphite to Cu with metal multi-foils

Graphite/Cu bonding is essential for the fabrication of graphite-based plasma-facing parts and graphite-type commutators. Transient liquid phase bonding of graphite/Cu has been conducted separately with Ti/Cu/Ti and Ti/Cu/Ni/Ti multi-foils. The interfacial microstructure and mechanical properties of the bonded joints have been characterized. For the joint with Ti/Cu/Ti multi-foils, complete melting of the Ti/Cu/Ti multi-foils and interdiffusion between the molten zone and the Cu substrate occur during the bonding process, leading to formation of Ti–Cu intermetallics in the bonding area. The liquid phase flowing toward the sidewall of the Cu substrate gives rise to a thickness of the bonding area far less than those of the as-received multi-foils. For the joint with Ti/Cu/Ni/Ti multi-foils, the bonding area can be divided into three parts (areas I, II and III). The bonding areas I and III comprise Ti–Cu intermetallics and Ti(Cu x Ni 1-x ) 2 , while the bonding area II consists of an Ni layer and two thin TiNi 3 reaction layers. The thickness of the whole bonding area is similar to those of the as-received multi-foils, indicating that addition of Ni foil can prevent the loss of liquid phase zone by inhibiting the excessive liquid phase formation. The addition of a Ni foil in bonding of the graphite/Cu may alleviate the joint residual stress by its intermediate coefficient of thermal expansion (CTE) to accommodate any thermal mismatch in the joint and by its superior ductility and plasticity, thus resulting in shear strength promotion of the joint with the Ti/Cu/Ni/Ti multi-foils by approximately 35% when compared to the Ti/Cu/Ti multi-foils.