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

Si₃N₄ ceramics have shown promising application prospects as the sealing materials for liquid metal batteries (LMBs). However, the joining of Si₃N₄ 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/Si₃N₄ 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/Si₃N₄ FGMs, with optimal layer numbers, were then utilized for fabricating symmetrical W/Si₃N₄/W FGMs. The thermal stress of the products can be effectively reduced by adjusting the MgO content of the central Si₃N₄ 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 × 10¹² Ω cm). This route for the fabrication of symmetrical W/Si₃N₄/W FGMs exhibits the advantage of high efficiency, and the products with excellent properties can be used as sealing materials for LMBs.