Fig. 1. Distribution of PPBs in the as-received and the pulsed samples. (a)-(c) the as-received sample. (d)-(f) the pulsed sample treated by parameter #1 (400 Hz; 45 μs; 1.14 × 108 A/m2; 10 min). (g)-(i) the pulsed sample treated by parameter #2 (400 Hz; 50 μs; 1.14 × 108 A/m2; 10 min). (j)-(l) the SEM/EDS mapping results of the typical PPBs in the as-received sample.

Fig. 2. Distribution of grain boundary carbides and γ′ phase in the as-received and the pulsed samples. (a, b) the as-received sample. (c, d) the pulsed sample treated by parameter #1 (400 Hz; 45 μs; 1.14 × 108 A/m2; 10 min). (e, f) the pulsed sample treated by parameter #2 (400 Hz; 50 μs; 1.14 × 108 A/m2; 10 min). The size and morphology of γ′ phase and grain boundary carbides unchanged under parameter #1. With the parameter higher, the volume fraction of γ′ phase and the number of grain boundary carbides decreased significantly.

Fig. 3. (a) Schematic diagram of the PPBs with chain-like structure which mainly consist of MC carbides. (b) The enlarged drawing of the spherical and ellipsoid precipitates that marked by the dashed rectangle in (a). (c)-(h) The current distribution around the precipitates with various geometric shapes and sizes: (c) r = 0.4; a = 0.4; b = 0.8, (d) r = 0.35; a = 0.35; b = 0.7, (e) r = 0.3; a = 0.3; b = 0.6, (f) r = 0.2; a = 0.2; b = 0.4, (g) r = 0.15; a = 0.15; b = 0.3, (h) r = 0.15; a = 0.15; b = 0.15. (i) The variation of the current density along the dotted line in (b) with the particle size reduction. (j) The variation of the change of the electrical free energy with the size reduction of the precipitates.

Fig. 4. (a, b) Schematic diagrams of the traditional treated and pulsed electric current assisted processes for the powder superalloys preparation, respectively. The hot extrusion and isothermal forging processes in (a) could be replaced by the pulsed electric current process in (b).