Improving the interface strength and fatigue property of W-Cu-steel brazed joint via induced interface alloying

Abstract

Heterogeneous W-steel joining components will produce brittle intermetallic compounds (IMCs) and significant residual stress in the interface. Adding a Cu interlayer serves as an effective solution. Nevertheless, the strengthening of W-Cu-steel joints is restricted because W-Cu and Cu-steel are members of binary immiscible and finite solid solution systems. Thus, accomplishing interface alloying by overcoming the positive generating energy of insoluble systems and opening up interatomic diffusion channels is a crucial issue to be addressed. In this work, casting and brazing technologies were incorporated into bonding W-Cu-steel to provide a high temperature field, as well as the dissolving and wetting of Cu-based liquid phase to refractory W. It is shown that the superior tensile strength of the W/Cu castings-steel brazed joints (∼264 MPa) was achieved, and the joint survived 1000 cycles of thermal fatigue under 1 MW/m². To assess the effects of brazing and casting on the W-Cu-steel joint, a detailed analysis was conducted on the mechanism of atomic diffusion in the joint interface. It is considered that in W-Cu joining, casting provided a higher thermodynamic driving force than brazing, thus achieving better interatomic diffusion and a wider microalloying region. Cu-steel joining achieved good alloying and forming dendritic extensions by intergranular diffusion. Based on the process optimization results, the feasibility of preparing the U-shaped first wall (FW) mock-up with W armor using brazing technology was verified. This study provides a new technological path, offering a major design and manufacturing guide for plasma facing components (PFCs).