Effects of boron addition on the microstructure and creep properties of a Ni-Fe-based superalloy weld metal alloy

Abstract

The role of boron in the creep properties and grain boundary characteristics in a new Ni-Fe-based weld metal suitable for advanced ultra-supercritical (A-USC) coal-fired power plant applications has been investigated. Ni-Fe-based filler wires without boron and boron-doped (50 ppm wt% boron) were prepared for this study. Boron-doped weld metals exhibited longer rupture lives and lower steady creep rates during the creep rupture tests at 750 °C / 380 MPa and 750 °C / 210 MPa. This study explains the improvement mechanism of boron on creep resistance from the perspective of the effect of boron on M _23 C _6 . Boron increased the nucleation rate of M _23 C _6 and participated in the formation of M _23 (C, B) _6 type boron-carbides. After creep deformation, boron still existed stably in the M _23 (C, B) _6 . The higher density of discrete M _23 C _6 particles due to boron addition could restrain grain boundary crack propagation and grain boundary sliding, and thereby improve the creep fracture resistance of the GH984G weld metal at 750 °C / (380/ 210 MPa).

Keywords

• superalloy
• weld metal
• creep
• boron
• M23(C
• B)6