Fabrication and properties of symmetrical W/Si3N4/W functionally graded materials by spark plasma sintering

• Symmetrical W/Si3N4/W functionally graded materials (FMGs) were fabricated. • The layer numbers and MgO content affected the structure and thermal stress of FGMs. • The W/Si3N4/W FGMs exhibited high flexural strength and electrical resistivity. • The W/Si3N4/W FGMs can be used as sealing materials of liquid metal batteries. Si 3 N 4 ceramics have shown promising application prospects as the sealing materials for liquid metal batteries (LMBs). However, the joining of Si 3 N 4 to the metal shell of LMBs is rather difficult because of the non-wetting property and mismatch of their thermal expansion coefficients (CTEs). Herein, to solve the above issue, W/Si 3 N 4 functionally graded materials (FGMs) were designed and fabricated via the spark plasma sintering (SPS) process. The effects of layer numbers and layer components on the phase composition, structure, and thermal stress of the FGMs were systematically investigated using both experimental and simulation methods. W/Si 3 N 4 FGMs, with optimal layer numbers, were then utilized for fabricating symmetrical W/Si 3 N 4 /W FGMs. The thermal stress of the products can be effectively reduced by adjusting the MgO content of the central Si 3 N 4 layer. As a result, the optimal product displayed good interface bonding between two adjacent layers and also exhibited high flexural strength (943.9 MPa) and electrical resistivity (2.0 × 10 12 Ω cm). This route for the fabrication of symmetrical W/Si 3 N 4 /W FGMs exhibits the advantage of high efficiency, and the products with excellent properties can be used as sealing materials for LMBs.