Weldability and Mechanical Properties of a Ni-Based Alloy for Future Fusion Applications
摘要
In order to stimulate greater fusion power output, China is independently designing the China Fusion Engineering Test Reactor (CFETR). The welded joints of the CFETR central solenoid (CS) tie-plates must exhibit a yield strength exceeding 800 MPa and a fracture toughness greater than 130 MPa m1/2, both at room temperature and at the ultra-low temperature of 4.2 K. Conventional stainless steels such as 316LN, N50, JJ1, and JK2LB cannot meet these requirements. Therefore, there is an urgent need to develop novel high-strength and high-toughness materials to satisfy the demanding requirements of the CFETR CS tie-plates. Precipitation-strengthened nickel-based alloys, notably for their high room-temperature strength and weldability, have great potential for the application of CS tie-plates. Based on the designed Ni-based alloy, we have successfully prepared the inner and outer CS tie-plates as well as the corresponding welding wire. The entire process of preparation, including smelting, refining, forging, hot rolling, and drawing, was fully established. The welded joint exhibited an exceptional combination of strength and toughness at both room temperature and 4.2 K with yield strengths of ~ 817.5 and ~ 1024 MPa, ultimate tensile strengths of ~ 1203.5 and ~ 1623 MPa, and fracture toughness values of ~ 146.5 and ~ 230 MPa m1/2, respectively. The microstructural analysis results suggest that both the base metal and the weld metal exhibit predominantly austenitic grains in the heat-treated welded sample with numerous precipitation of γ′-Ni3(Al,Ti), γ″-Ni3Nb, and (Nb,Ti)C phases mostly on grain boundaries, which enabled a significant increase in the strength. This study will present experimental data on welding joints and discuss the feasibility of developed Ni-based alloy as a high-magnetic field CS tie-plates material for next-generation fusion reactors.