Effect of joining temperature and holding time on microstructure and shear strength of Ti2AlC/Cu joints brazed using Ag-Cu filler alloy

The present study investigated the effect of brazing temperature and holding time on the microstructure and mechanical properties of Ti2AlC-copper joints brazed with Ag-Cu filler alloy at 800-900 degrees C for 10 min and held for different times at 850 degrees C. The representative structure of the joints was Ti2AlC/interaction area in the Ti2AlC substrate/brazing layer/diffusion area of the copper substrates/Cu. The brazing layer was composed of Cu-rich phases, AlCu2Ti intermetallic compounds and Ag[Cu] solid solutions. With increasing brazing temperature, more filler alloy was infiltrated into the ceramic substrate and reacted with Ti2AlC, accelerating the decomposition of Ti2AlC and the formation of Ti3AlC2, TiC and AlCu2Ti reaction phases. Moreover, more copper substrate was dissolved into the filler alloy; thus, more Cu-rich phase and AlCu2Ti were produced in the brazing layer. Moreover, the width of the brazing layer was reduced, while the widths of both the interaction area and diffusion area increased. As the brazing temperature was increased, the shear joint strength increased and then decreased. By prolonging the holding time, the widths of both the interaction area and the diffusion area were increased, while the width of the brazing layer was held constant at approximately 50 mu m. Neither the structure nor the shear strength of the joints was influenced by the holding time. The optimum brazing parameters for joining Ti2AlC ceramic to copper with Ag-Cu filler alloy were 850 degrees C for 40 min. The joints obtained exhibit a maximum shear strength of 203.3 MPa. (C) 2012 Elsevier B.V. All rights reserved.