Investigation of the segregation mechanism and mechanical properties of laser powder bed fusioned CM247LC Ni-superalloy

Segregation plays a crucial role in crack initiation in Ni-superalloys, yet the surface segregation of Al, Hf, and Ta in these alloys has not been previously documented. This study investigates the melt pool microstructure, phase distribution, defects, and mechanical properties of CM247LC Ni-superalloys fabricated through laser-based powder bed fusion (L-PBF). The findings indicate that during solidification, misoriented columnar dendrites create segregation channels that facilitate the flow of Al and refractory elements to the melt pool surface, resulting in the formation of bubble-shaped Al2O3+Ta(Hf)O2 primary surface segregation oxide. Subsequently, the depression and Marangoni flow induced by the next laser scan transform these primary segregation oxides into line-shaped redistributed oxides. These redistributed oxides, when positioned between the scan tracks of subsequent layers, become difficult to remelt and remain as unmelted oxides within the sample, thereby compromising its high-temperature performance. By parameters optimisation, the high-temperature tensile properties of 1105 MPa tensile strength and 8.5 % elongation in the horizontal direction, and 1100 MPa, 15 % elongation in the vertical direction were achieved.