Reactive composite brazing of C/C composite and GH3044 with Ag–Ti mixed powder filler material

In this study, a novel Ag–Ti reactive composite brazing technology was employed to join carbon fiber reinforced carbon matrix composite (C/C) to Nickel-based superalloy GH3044. The microstructural evolution mechanism and the effects of process parameters on the microstructures and shear strength of the brazed joints were investigated systematically. The results showed that, during the brazing holding stage, Ti (α-Ti) in the liquid phase would convert to β-Ti (above 1020°C) or react with Ag formed AgTi (below 1020°C). Solid phase β-Ti or AgTi inhibited the loss of the molten filler material, thus forming a thicker interlayer, which was beneficial to relieve the residual stress of the joints. After brazing, an Ag matrix composite interlayer reinforced by in situ synthesized phases and a few residual Ti particles could be obtained. Notably, the reinforcing phases were various with different brazing parameters. Under weaker parameters (lower Ti content, lower temperature and shorter holding time), the reinforcing phases were mainly in situ synthesized AgTi phase and residual Ti particles, with which the Ag matrix composite interlayer had good plasticity and low coefficient of thermal expansion. As a result, the residual stress of the joints was further effectively relieved. Under stronger parameters, the reinforcing phases were mainly brittle phases Ti2Ni and Cr1.93Ti1.07, which increased the brittleness of the composite interlayer. The maximum shear strength of the joints reached 45.8 MPa brazed at 1020°C for 30 min using Ag–20Ti (Wt.%).