Creep strength and toughness synergistic strengthening mechanism investigation of the Inconel625/ BNi-2 brazed joint

Abstract

Creep strength and toughness synergistic strengthening mechanism of Inconel625/BNi-2 brazed joint is investigated based on the post-brazing solid solution heat treatment (PSSHT). The heat treatment temperature of 1150 °C is adopted. The results show that borides in brazed joint are eliminated and broken gradually with the increasing of PSSHT time, and the elements are more uniformly distributed. The brazed joint with PSSHT time of 3 h has the longest creep life and the highest toughness, followed by those with PSSHT time of 6 h and 0 h, respectively. Elements homogenization can promote the creep strength and toughness of the brazed joint. While more PSSHT time will increase the grain size of brazed joint, and thus it degenerates the creep strength and toughness of the brazed joint. Although the borides can increase the risk of joint crack failure, the proper amount of punctate borides distribute along the grain boundary or in the interior of the grain can serve as the pinning points to slow down the dislocation movement of grain boundary, so as to improve the creep strength of brazed joint. Therefore, creep strength and toughness strengthening of the brazed joint caused by PSSHT is the synergistic action of element homogenization, borides distribution and grain size. The solid solution heat treatment time of 3 h at 1150 °C is a recommended heat treatment procedure.

Keywords

• Solid solution heat treatment
• Elements homogenization
• Borides distribution
• Creep strength and toughness
• Pinning effect