Microstructures and intermediate temperature brittleness of newly developed Ni-Fe based weld metal for ultra-supercritical power plants

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

“…As shown in figure 8, the creep rupture behaviors of the samples with or without boron addition were both intergranular rupture, which means that the grain boundaries were the weak area of the GH984G weld metal under the 750 °C test environment. This phenomenon is similar to that studied by Wu et al [14]. Wu et al proposed that intergranular fracture mainly took place at around 750 °C in the GH984G weld metal.…”

“…The addition of boron improved the creep resistance of the weld metal, but it did not change the main failure mechanism of intergranular fracture of weld metal at 750 °C, namely, the fact that the grain boundaries are the weak areas of the weld metal at 750 °C [14]. These results suggest that, although boron did not change the main fracture mechanism, it effectively inhibited the propagation of grain boundary cracks, thus increasing intragranular deformation, which was also the reason for the increase of elongation after the addition of boron.…”

“…As shown in figures 5(a) and (c), the width of the width of the M 23 C 6 grains is about 50 nm in both boron-free and boronbearing specimens. The spherical phase precipitated in intragranular was the γ′ phase, which is the main strengthening phase in the weld metal [14].…”

“…Therefore the weldment will be used with segregated microstructure, non-equiaxed grains, and non-equilibrium primary phases, which may cause the stress-rupture properties of the weld metal to be inferior to those of the base metal. Moreover, at the operating temperature of 700 °C ∼ 750 °C, the grain boundary becomes the weak area of this alloy [14]. Therefore, improving the stress rupture property of the weld metal is a compelling issue in the design of the welding materials.…”