Microsegregation of a new Ni-Co-based superalloy prepared by electron beam smelting layered solidification technology and its homogenization behavior

The electron beam smelting layered solidification technology (EBS-LST) is put forward to fabricate a new Ni-Co-based superalloy with less segregation. The microstructures and homogenization behavior of the prepared ingot were studied. The experimental results show that the cross-sectional microstructure of the EBS-LST alloy consists of four typical areas, namely melted zone (MZ), partially fusion zone (PFZ), heat affected zone (HAZ), and bottom layer (BL). During the EBS-LST solidification process, the cooling rate is calculated to be 22.3 k/s according to the well-established model associated with secondary dendrite arm spacing. It can be inferred that the EBS-LST will reduce the solidification time, and thus eliminating the macrosegregation, and weaken the microsegregation of the ingot effectively. The effect of homogenization treatment on the microsegregation and microstructure evolution of the alloy is also studied. The residual segregation index equation during homogenization is constructed for the diffusion behavior of the strongly segregated elements of Ti and W. The diffusion coefficients DW and DTi are calculated as 3.9 × 10−15 m2·s−1 and 5.4 × 10−15 m2·s−1, respectively.