Effect of High Density Current Pulses on Microstructure and Mechanical Properties of Dual-Phase Wrought Superalloy

doi:10.1007/s40195-021-01211-7

Abstract

Abstract:

In this study, high density electric current pulse (ECP) treatment was introduced instead of the conventional solution treatment, and the γ′ phase was completely dissolved under the ECP treatment within only several milliseconds at 1148 °C. Due to the extremely short treatment time and high cooling rate, the growth of γ-phase matrix grain and γ′ phase precipitate was effectively retarded. By comparing with the conventional heat process, the grain size of ECP treated sample was controlled to about 15 μm, the size of the re-precipitated γ′ phase reduced from 65 to 35 nm, and the number density of γ′ precipitate increased from 1.46 × 10 ⁸ to 3.03 × 10 ⁸/mm². The Vickers hardness, ultimate tensile strength and yield strength of the ECP treated sample were significantly improved. According to the theoretical derivation of kinetics, the ECP treatment introduces an extra electrical free energy which promoted the dissolution of γ′ phase. The ECP treatment may provide a new method for solution treatment of the Ni-based superalloy.

Key words: Electric current pulse, Superalloys, Precipitation, Grain size, Mechanical properties

Jun Zhang, Ji-De Liu, Xin-Fang Zhang, Chuan-Yong Cui, Jin-Guo Li, Yi-Zhou Zhou, Bao-Quan Wang, Jing-Dong Guo. Effect of High Density Current Pulses on Microstructure and Mechanical Properties of Dual-Phase Wrought Superalloy[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(12): 1635-1644.

Figures/Tables 15

Table 1 Chemical composition of the studied superalloy (wt%)

Ni	Co	Cr	Ti + Al	Mo	W	C + B + Zr
Bal.	20-26	13-15	7.72-8.40	2.4-2.8	1.1-1.3	0.04-0.11

Fig. 1 Microstructure and element distribution of the as-forged specimen

Fig. 2 a Schematic diagram of the ECP treatment, b typical waveform of the ECP

Table 2 Solution treatment parameters

Sample	Solution treatment
E1	j_max = 6.3 kA/mm²
E2	j_max = 6.7 kA/mm²
H1	1100 °C, 4 h, AC
H2	1160 °C, 4 h, AC

Fig. 3 SEM images of samples after different solution treatments: a H1, b H2, c E1 and the temperature curve, d E2 and the temperature curve

Fig. 4 γ′ phase volume ratio in different samples (d?≥?100 nm)

Fig. 5 γ′-phase particle size distribution of samples H2 and E2

Fig. 6 LSCM of samples under aging treatment after different solution treatments: a H1, b H2, c E1, d E2

Fig. 7 Average grain size of different solution treatment samples after aging treatments

Fig. 8 SEM images of sample E2 after aging treatments: b-d enlarged views of A, B, C in a

Table 3 Main element contents at marked point in sample E2 after aging treatments

Position number	Main elements (wt%)
Position number	Al	Ti	Cr	Co
1	1.24	4.55	16.53	26.54
2	1.29	5.81	14.06	25.53
3	1.51	7.47	12.8	24.37

Fig. 9 Hardness change of the samples before and after aging treatments

Fig. 10 Stress-strain curves of the samples after aging treatment

Table 4 Mechanical properties of samples after heat treatments

Sample	Ultimate tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
H1	1610.3	1204.0	21.03
H2	1044.8	898.2	8.12
E1	1590.1	1251.8	14.45
E2	1657.1	1315.6	17.23

Fig. 11 SEM images of fracture morphologies: a H1, b H2, c E1, d E2

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