Advanced high-temperature resistant (RT-1000 degrees C) aluminum phosphate-based adhesive for titanium superalloys in extreme environments

To facilitate the repairing and connecting processes for titanium superalloys, an advanced high-temperature resistant adhesive that can be converted to a composite of intermetallics and ceramics was prepared by modifying aluminum phosphate-based adhesive with various additives. The composition evolution of the adhesive, the structure changes in the bonding layer, the reaction process at interfaces and the fracture mode of joints are comprehensively studied to explore the bonding mechanism. The results showed that the chemical bonding based on the formation of TiSi and Ti5Si4 started to work at 600 degrees C, and became the crucial bonding mechanism at higher temperatures. A diffusion reaction layer with size up to 6 mu m effectively alleviated the difference of composition and performance between alloy substrate and adhesive. From RT to 900 degrees C, the coefficient of thermal expansion (CTE) of adhesive matched well with that of alloy substrates, and the difference of their CTE was always lower than 2 x 10(-6) k(-1). The bonding strength reached similar to 16 MPa after pre-treatment at 900 degrees C without pressure, and remained over 13 MPa within the common operating temperature range (400-600 degrees C) of TC4 alloys. Without any pre-treatment, the adhesive could still provide above 5 MPa in range of RT-600 degrees C.