Boride evolutionary behavior and mechanism in the TLP repaired IN738 superalloy with crack-like defects

Boride evolution in the transient liquid phase (TLP) repaired cracks for IN738LC alloy had important influence on mechanical properties. The microstructure of the repaired crack contained two typical zones: isothermal solidification zone (ISZ) and diffusion affected zone (DAZ). There were blocky and acicular borides with hexagonal crystal structure in the DAZ, and boride morphology depended on the interfacial distance, Cr/B content, and aging time. i) As the distance from the ISZ/DAZ interface increased, blocky borides gradually decreased and acicular borides began to form. ii) When Cr and B were sufficient, blocky borides firstly formed. When the content decreased to a certain extent, borides would not form. iii) As aging time increased, the amount of blocky borides gradually increased due to the diffusion of B. Meanwhile, acicular borides began to form along (111) plane, which could effectively reduce the interfacial energy.