Microstructure and hot ductility behavior of Ni-based superalloy U720Li with boron addition

High-alloyed superalloy U720Li is difficult to be processed through the conventional cast and wrought route. Boron is an important strengthening element for superalloys, but the role of boron in the hot ductility of U720Li alloy is not clear. This study is focused on the effect of boron addition, in the range of < 0.0005 wt%-0.0240 wt%, on the microstructure and hot ductility behavior of superalloy U720Li. It is found that boron addition significantly increases the content of eutectic (gamma + gamma ') and greatly affects the degree of continuity of the grain boundary eutectic (gamma + gamma ') precipitation. Boron addition dramatically worsens the 1100 degrees C tensile ductility of conventional cast U720Li alloy and causes a change in tensile fracture mode from transgranular to intergranular. The eutectic (gamma + gamma ') represents the most effective site for crack initiation. Boron deteriorates the hot ductility mainly by promoting the continuous precipitation of eutectic (gamma + gamma ') along the grain boundary.