Ni-based superalloy synergistic strengthened by in-situ nano-carbides and residual graphene fabricated via laser powder bed fusion

With the increase in power of the industrial gas turbine and thrust-weight ratio of aeroengine, the conventional strengthening method of adding refractory elements into superalloys has become difficult to meet the demands for the higher mechanical properties. A novel Ni-based superalloy was designed with enhanced strength and hardness based on the graphene nanosheets (GNs) synergistic in-situ nano-carbides strengthening in the present work. Nano-carbides were induced by in-situ reaction of the GNs with alloy powders during additive manufacturing. The microstructure and thermophysical properties of different alloys with 0.1wt.% GNs and without GNs were investigated by SEM, EBSD, TEM, differential scanning calorimetry (DSC), and small angle neutron scattering (SANS). Residual GNs were also detected by SANS and DSC. The nano-carbides are uniformly distributed in the matrix and combine with residual GNs to refine the cellular structure. Compared with the original alloy (ASE100), the hardness of the alloy with 0.1wt.% GNs (ASE100-0.1GN) is increased by 31 HV (from 315 HV to 346 HV), and the yield tensile strength is increased by 86 MPa (from 756 MPa to 842 MPa). The GNs react with alloy melt in the molten pools to generate nano-carbides under the Marangoni effect during manufacturing process. The dispersion nano-carbides are distributed at both grain boundaries and within grains, effectively hindering the movement of dislocation and enhancing the strength of alloy.