Long-lasting action mechanism of 3D skeleton regulated the residual stress fluctuations in SiCf/SiC heterogeneous joints

SiCf/SiC composites could improve the operating temperature and thrust-weight ratio of aero-engines, and their effective joining with superalloys can solve itself problem of poor machinability. However, large residual stress in the brazed joint deteriorates the mechanical performance. Graphene-reinforced Cu (G-Cu) foam was introduced as an energy-absorbing interlayer to relieve the residual stress in this study. Graphene played a protective clothing role, and G-Cu foam skeleton was less prone to collapse and remained intact, and had a more durable plastic deformation capacity. By using FIB and TEM to accurately observe the brazed joint, it was found that the nano-sized skeleton was not interrupted and still maintained its strong foam structure. Introducing G-Cu foam had played a great role in the optimization of the microstructure. The distribution of bulk Cu(s,s) became more uniform, and TiCu was uniformly protected around Cu(s,s). The G-Cu foam had the low coefficient of thermal expansion (CTE), which decreased the residual stress from 340 MPa to 275 MPa. The G-Cu foam balanced the difference in elastic modulus between base materials, and the brazed joint obtained the ductility-rigidity-ductility multilayer structure. By introducing the diversified optimization mechanism of energy-absorbing interlayer, the synergistic improvement of microstructure-stress-performance was realized, and joints with good structure, low stress, high strength and high toughness were obtained.

Automated summary

SiCf/SiC composites can improve the operating temperature and thrust-weight ratio of aero-engines, and their effective joining with superalloys can solve the problem of poor machinability. In this study, graphene-reinforced Cu (G-Cu) foam was introduced as an energy-absorbing interlayer to relieve the residual stress in the brazed joint. The G-Cu foam played a protective role, and its foam structure remained intact, leading to good microstructure and improved performance.