Fig. 1. Macroscopic morphologies of DD6 single crystal alloys. (a) Single-channel single-layer deposition; (b) single-channel 5-layer deposition

Fig. 2. Dendrite morphologies in single-channel single-layer deposition area. (a) Schematic of area positions; (b) bottom area; (c) middle area; (d) CET area at top

Fig. 3. Orientation distribution and KAM plot of DD6 single crystal alloy after single-channel 5-layer deposition. (a) Orientation distribution; (b) KAM plot

Fig. 4. Dendrite morphologies in I‒III regions and corresponding local orientation distributions. (a) Dendrite morphologies; (b) local orientation distributions

Fig. 5. Schematic of Vickers hardness test points of DD6 single crystal alloy after directed energy deposition and hardness values.(a) Schematic of test points; (b) hardness values

Fig. 6. Typical microscopic morphology in CET region at top. (a) Microscopic topography; (b) partial enlargement

Fig. 7. Thermophysical property parameters and phase diagram. (a) Thermal conductivity; (b) specific heat capacity;(c) viscosity coefficient; (d) phase diagram

Fig. 8. Thermal history simulation during single-channel 5-layer deposition of DD6 single crystal alloys. (a) Sweep strategy, finite element model, and selection positions of measured points during single-channel 5-layer deposition; (b) temperature changes at seven measured points during deposition process; (c) temperature gradient changes at seven measured points during deposition process

Fig. 9. Formation mechanism of γ/γ′ eutectic band in CET area

Fig. 10. Contents of different elements in γ/γ' eutectic band and dendrite core. (a) Line scanning directions; (b) line scanning result of element W; (c) line scanning result of element Re; (d) line scanning result of element Mo

Fig. 11. Effects of heat flow inside molten pool on element distribution and eutectic coarsening. (a) Temperature gradient and convection morphology of molten pool during deposition of DD6 single crystal alloy; (b) element content; (c) directional coarsening of γ/γ 'eutectic due to chemical gradient

Fig. 12. Microscopic morphologies of CET area in central area. (a) Fusion zone between dendrite core and interdendrite; (b) dendrite core area; (c) interdendrite area