Diffusion brazing repair of IN738 superalloy with crack-like defect: microstructure and tensile properties at high temperatures

In this study, tapered slots with an opening width about 200 μm were artificially fabricated in IN738LC superalloy to imitate service cracks. The ‘cracks’ were repaired by diffusion brazing with a Ni–Cr–Co–Al–Ta–B filler alloy at 1150°C and then heat treated at 1180°C (HT-A) and 1190°C (HT-B), respectively. A joint with uniform microstructure, chemical composition and hardness was obtained using HT-B. The mechanisms of the borides evolution during homogenisation were discussed. The tensile strength of the HT-B joint tested at 20, 600 and 800°C reached up to approximately 96, 90 and 87% of the base metal, respectively. The fracture modes of the joints tensile tested at various temperatures were discussed.