Mo-Ni foam interlayer deposited pyrolytic carbon for brazing C/C and nickel-based superalloy

Abstract

C/C composites possess both lightweight and high-strength properties, and joining them with superalloys can reduce the mass of the joints and construct ultra-high heat flux lightweight cooling components, which are widely used in the hot end of a nuclear reactor. Nonetheless, significant residual stress caused by thermal mismatch is the counterpart when brazing C/C composites and metals. This increases the initiation of the joint cracks. In this study, a new method of deposition pyrolytic carbon (PyC) on the Mo-Ni skeleton to help braze C/C composites and nickel-based superalloys was proposed. With the protection of a uniformly distributed PyC layer, the corrosion and dissolution of the metal skeleton by the brazing material can be effectively mitigated. The low coefficient of thermal expansion (CTE) of the PyC layer mitigates the thermal mismatch of the joint, while the high plastic deformation capacity of the skeleton effectively mitigates the residual stresses. The two mechanisms cooperate to increase joint strength. To enhance the chemical bonding of the joint, a modification of Ti powder was implemented. The synergistic reinforcement of PyC-modified Mo-Ni foam (C-MN) and Ti powder-modified brazing material was utilized to effectively enhance the shear strength of the joint to ∼41 MPa, a 163 % improvement over unmodified joints. This work can provide a new idea for the preparation of high-performance C/C composites and joining materials for metals.