Polycarbosilane-modified phosphate adhesives for porous Si3N4 ceramic pressure-free bonding at high temperatures

Si₃N₄ ceramics are widely employed in the aerospace and automotive sectors owing to exceptional mechanical performances, anti-oxidant nature, and corrosion resistance properties. However, their brittleness makes manufacturing complex components challenging, while the intricate nature of welding restricts its use. A Si₃N₄ ceramic adhesive joint capable of withstanding high-temperature conditions was formed under ambient conditions. Polycarbosilane was introduced into the phosphate adhesive to improve high-temperature thermal matching between the adhesive and substrate, At 600 and 800 ℃, the compressive shear strength increased by 25 % and 83 %, respectively. After 48 h at 1000 ℃, the compressive shear strength was 8.6 MPa, indicating excellent oxidation resistance. The adhesive penetrated the matrix pores under capillary action, forming network bonding, and an interfacial reaction generated Si₅AlON₇, buffering thermal stress. This represents the first phosphate adhesive for bonding Si₃N₄ ceramics, demonstrating excellent forming capabilities, with bond strengths comparable to that of conventional welds, showing high potential for engineering applications.