Numerical Simulation And Experimental Verification For The Residual Stress Distribution Of Brazed Joints Between Tungsten And Ferrtic Steel

New requirement of joining tungsten(W) to ferritic steel(FS) was put forward by the design of the divertor components of demonstration reactor (DEMO). However, significant differences in physical properties (coefficients of thermal expansion and elastic modulus et.al) between W and FS would result in high thermal residual stress in the W/FS joints leading to the failure of the joints. Therefore, the connection of W and FS has being an urgent problem in DEMO. Brazing is a suitable way to realize the joint of W and FS. Analysis of the residual stress distribution in W/FS brazed joint is critical to obtian high quality W/FS brazed joint.In the present work, the2D and3D residual stress distribution of W/FS joints were simulated by ANSYS software. The influences of inter layers on residual stress distribution in W/FS joints were analyzed. The residual stress was determined by nanoindentation method. Finite element simulation results were verified by the experimental data. The conclusions drawn from our present work are as follows:(1) The maximum radial compressive residual stress was in tungsten matrix near the brazing seam, while the maximum radial tensile residual stress was in the brazing foil near free boundary. Minor axial residual stress distributed in the internal area of the joints. The distribution of circumferential residual stress was similar to that of radial residual stress.(2) The radial compressive residual stress in tungsten matrix can be efficiently reduced by soft Cu interlayers; and the thicker the Cu layer, the less the radial compressive residual stress. But excessive thickness of Cu interlayer leaded to the huge radial tensile residual stress in the W-Ni reaction layer. The maximum tensile stress in the W-Ni reaction layer of W/0.5Cu/FS brazed joint reaches up to769MPa, but the tensile strength of joint was only89MPa. Regardless of thickness, Ta interlayers have less influence on the residual stress of the joints than that of soft Cu interlayers.(3) A reliable brazed joint of W and FS could be achieved by Cu and Ta interlayer. The fracture sourcesof W/FS brazed joints were in the tungsten matrix near the brazing seam, which agrees reasonable well with the finite element results. The maximum tensile strength was obtained in the W/0.2FeNi/FS brazed joint, up to310.67MPa, while minimum tensile strength is the direct brazed W/FS joint (154.9MPa).The tensile strength of W/0.03Cu/FS (267.52MPa) and W/0.5Ta/FS were267.52MPa and256.45MPa, respectively. The strength distribution was consistent well with the simulation distribution of residual stress in W/FS brazed joints.(4) Good consistency of2D and3D simulation results was obtained. The average surface residual stress determined by nanoindentation gradually decreases from the edge to center, which, again, agrees well with the finite element analysis.