Study on brazing connection process and mechanism between TiAl and surface densified porous Si₃N₄ ceramics

Porous Si₃N₄ (p- Si₃N₄) ceramics are ideal radome materials, while TiAl alloys are preferred for radome connecting rings, but their direct brazing suffers from filler infiltration. Herein, a dense coating composed of Si₃N₄ particles and Y-Al-Si-O glass phase was fabricated on porous Si₃N₄ via gas-pressure sintering. TiAl alloy was vacuum-brazed to the surface-densified porous Si₃N₄ (d-p-Si₃N₄) using AgCu-2wt.%Ti filler. The interfacial microstructure, mechanical properties and joining mechanism were systematically investigated. The results show that the dense coating effectively inhibits filler infiltration, forming a three-layer joint structure: TiAl/AlCu₂Ti/Ag (s,s)+Cu(s,s)/TiCu₄+TiN + TiO/d-p-Si₃N₄. The joint shear strength first increases and then decreases with rising temperature and prolonged holding time, reaching a maximum of 25.3 MPa (66% higher than that of the unmodified joint) at 880 °C for 15 min. The joining mechanism is dominated by Ti dissolution, diffusion and reactions with Si₃N₄ and glass phase. This method is suitable for the vacuum brazing of porous silicon nitride ceramics and TiAl alloys, and can offer a reference for the joining of similar porous ceramic/metal systems.