Fig. 1. (a) The samples with cube-shape and dimensions of 10 mm × 10 mm × 10 mm built on a base plate with the size of 150 mm × 150 mm × 10 mm and (b) process parameters of each sample shown in the corresponding position.

Fig. 2. Schematic diagrams of the modeling simplification for numerical simulation of thermal history: (a) the moving-spot heat source was approximated as an equivalent plane heat source; (b) the layer-by-layer building was simplified as bulk-increment.

Fig. 3. (a) EBSD phase map of vertical cross-sectional microstructure and (b, c) EBSD pole figures of selected ε grain and original γ grain at the lower part of the as-PBF-EB-built sample. The process parameter is P = 600 W, V = 300 mm/s, loff=455 μm.

Fig. 4. Selected samples exhibiting typical microstructure locates at (a) axisymmetric positions with respect to the base plate; (b) the field-of-view; (c, d) EBSD IPF maps and phase maps of vertical cross-sectional microstructure in different depicted in (b) parts along the building height. The process parameters are: P = 100 W, V = 300 mm/s, loff = 125 μm (Sample A); P = 1000 W, V = 300 mm/s, loff =750 μm (Sample B).

Fig. 5. Experimental thermal history during the PBF-EB process at the bottom center of the base plate measured by a thermo-couple equipped in the building chamber.

Fig. 6. Top view of the simulated temperature field of the base plate. The base plate was heated by an equivalent plane heat source until the temperature in the bottom center reached 1098 K.

Fig. 7. Simulated temperature fields of (a) Sample A and (b) Sample B during the building process. (c, d) The evolution of temperature at the center position in each increment of (c) Sample A and (d) Sample B.

Fig. 8. Isothermal TTT curve of the γ → ε diffusional-massive transformation. The red and green curves present the start and end of the transformation, respectively. The building period of PBF-EB was additionally annotated. The temperature ranges that Sample A and Sample B underwent during PBF-EB are annotated on the right side.

Fig. 9. EBSD pole figures taken from the γ and ε phases in the middle and lower parts of (a) Sample A and (b) Sample B.

Fig. 10. Histograms of misorientation angle between adjacent ε phase in (a) Sample A and (b) Sample B.

Fig. 11. EBSD IPF maps and phase maps of vertical cross-sectional microstructure in the sample almost without the ε phase. The process parameter is p = 1000 W, V = 100 mm/s, loff=900 μm.