Study On Diffusion Bonding Of Plasma Facing Materials Tungsten And Structural Material MA956 Steel

In this paper,W and MA956 steel were diffusion bonded by efficient Spark Plasma Sintering technique.The effects of holding time,diffusion temperature and interlayer on microstructure and mechanical properties of diffusion bonded W/MA956 steel joints are studied.W and MA956 steel was successfully diffusion bonded with titanium（Ti）interlayer with a bonding pressure of 10 MPa,holding time ranged for 10 to 30min,and bonding temperature changed from 850 to 950℃.The W/Ti/MA956 joint consisted of W/Ti solid solution layer,Ti interlayer and the intermetallic layer between Ti/MA956 steel.The optimum bonding parameter of SPS technique was 900℃,20 min,10 MPa,and the shear strength of joints was up to 228 MPa.The joints all fractured at the Ti/MA956steel interface with a brittle fracture mode.With the rising of holding time or bonding temperature,the type and quantity of intermetallic compounds increased,and two layers of intermetallic compounds,Fe Ti,Fe₂Ti and Cr₂Ti,were formed.W/MA956,W/Ni/MA956 and W/Nb/Ni/MA956 steel SPS joints were obtained at 900℃ and 20MPa.The shear strength of the joint with composite interlayer Nb/Ni was the lowest,which is only 132.3 MPa,and the fracture of the joint occured at the W/Nb interface.It was found that Nb and W are large size atoms with high melting points,and the diffusion channels are not easily formed at a relatively low temperature.The residual stresses of W/MA956 steel diffusion bonded joints with different interlayer were simulated by ANSYS software.The results showed that the maximum residual stress of the joints located at the W substrate adjacent to the joining interface,the design of composite interlayer Nb/Ni can reduce the residual stress of joint greatly.When cooling from the bonding temperature,the Nb interlayer would transfer some residual stress from W substrate and the soft Ni interlayer would relieve the residual stress by plastic deformation.when the bonding temperature is raised to 1050℃,the average shear strength of diffusion bonded joints was 113.7 MPa,170.5 MPa,303 MPa,respectively.The design of the composite interlayer Nb/Ni greatly improved the mechanical properties of the joint.Brittle and hard intermetallic compounds were formed at the Nb/Ni interface,and the joint fractured at the Nb/Ni interface with a brittle fracture mode.