Graphene-coated copper foam interlayer for brazing carbon/carbon composite and niobium

Problems such as poor structural integrity, inhomogeneous dispersion, and agglomeration of graphene in the brazing seam are typically encountered for graphene additives in a brazed joint interface. To resolve these problems, a plasma-enhanced chemical vapor deposition process was employed for in-situ preparation of a high-quality graphene-coated copper (Cu) foam composite interlayer prior to be applied for brazing carbon/carbon composite and niobium. The prepared graphene and the brazed joints were characterized via Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results revealed that graphene was evenly distributed in the brazing seam with the help of the Cu foam, which was characterized by interconnected porosity. Simultaneously, the excellent chemical inertia of graphene inhibited the collapse of the Cu foam, based on which the thermal residual stress in the joint was effectively mitigated due to the synergistic reinforcement effect of the Cu foam (with good plastic deformation capacity) and graphene (with extremely low coefficient of linear expansion). This effect led to significant improvement in the average shear strength of the joint.