Alloy Design and Development of a Novel Ni-Co-Based Superalloy GH4251

The need to develop new high-temperature materials has increased significantly in the last decade owing to the demand of higher engine operating temperature. This demand has motivated the development of a new Ni-Co-based superalloyNi-Co based superalloys GH4251 with service temperature up to 700–800 °C. Based on disk alloy U720Li, the GH4251 alloy is designed by adjusting the content of Co, Cr, Ti, Nb, and other elements. On the one hand, by increasing the Co content to 25 wt. %, the stacking fault energy is effectively reduced, which makes it easy to form nano-twins and other substructures that strengthening the alloy together with γ′ precipitates. The yield strengthsYield strength of the newly designed alloy can achieve 1100 MPa at 750 ℃ and the creepCreep-rupture life is more than 500 h at 750 ℃ under 530 MPa with fine grain sizeGrain size (ASTM 8), which is superior to U720Li. On the other hand, a certain Nb element is added to replace Ti element, which can reduce the γ′solvus temperature and its precipitating dynamics, along with a changed thermal deformation behavior caused by lower stacking fault energy, leading to a significant better hot work ability and weld ability compared with U720Li. Besides being used as disk or ring forgingsForging, this novel GH4251 alloy can also be well processed by additive manufacturingAdditive manufacturing due to its low cracking tendency.