Factors affecting strength of dissimilar TiAl/Ni-Si-B/Ni-based superalloy brazed joint

This paper addresses the process-microstructure-strength correlation during dissimilar brazing of TiAl alloy to IN738 Ni-based superalloy using Ni-4Si-3.2B filler metal. The solid/liquid reactions, solidification phenomena, and solid-state phenomena are analyzed. The thickness of the athermal solidification zone and reaction layer at different bonding conditions (holding times and temperatures) determined and analyzed using a Larson-Miller parameter (LMP). It was resulted that the shear strength of the joint can be formulated regarding bonding temperature and holding time through using LMP. It was found that the sizes of athermally solidified zone and reaction layer are two key factors controlling the joint strength. The shear strength of the joints made at lower brazing temperature/times (i.e., low LMP) is controlled by the width of hard centerline eutectic borides. However, the width of the reaction layer is the dominating factor for the strength of the joints made at higher temperatures /times (i.e., high LMP). In addition, the highest shear strength of the joint was obtained in the optimum value of LMP.