2002 Volume 66 Issue 7 Pages 792-798
C/C composites were bonded to nickel in vacuum, using an RF-induction furnace, with joining temperature, keeping time and joining compressive stress as variables. C/C composites with different carbon fiber orientations and heat treatment temperatures were used. The bending strength of the C/C composite/nickel joints was investigated. The fracture surface of the joints was observed using a scanning electron microscope. X-ray diffraction was performed on the joining surface of C/C composites. Changes in the microstructure and hardness of nickel near the joining interface were investigated. On the basis of the results of these experiments, the influences of carbon fiber orientation and graphitization on the solid-state bonding of C/C composite to nickel were examined.
A large difference in thermal expansion coefficients between the longitudinal section of carbon fiber and nickel results in delamination at the interface. In the bending test, when the longitudinal section of carbon fiber is parallel to the joining surface, slip due to crystallographic anisotropy occurs. Therefore, good bonding between the longitudinal section of the carbon fiber and nickel is not achieved. On the other hand, good bonding to nickel along the cross section perpendicular to the carbon fiber axis becomes feasible. Therefore, in plain woven carbon fiber-reinforced carbon composite/nickel joints, the bending strength is low, while in unidirectional carbon fiber-reinforced carbon composite/nickel joints, the bending strength is equivalent to that of C/C composite.
The degree of graphitization affects the joining quality. Strong bonding of C/C composite to nickel is accomplished with the progress of graphitization. The bending strength of the joint is equivalent to that of C/C composite.
The bending strength of C/C composite/Ni joints is affected by the joining temperature, keeping time and joining compressive stress, because these factors are related to full contact of joining surfaces and diffusion of carbon atoms from C/C composite into nickel.
