Unravel the Spinodal Decomposition Kinetics in (FeCoCrNi)85(AlCu)15 Alloy through Small-Angle Neutron Scattering

doi:10.1007/s40195-024-01793-y

Abstract

Abstract:

High entropy alloys (HEAs) constituted of single solid solution phase, but remains chemical inhomogeneity in nature due to its multi-principal composition. Currently, existence of nanoscale spinodal decomposition (SD) phase in matrix was found to have significant impact on the properties of HEAs. Nevertheless, the morphology evolution and the kinetics of SD is not clear, which hinders in-depth understanding of the structure–property relationship. In this study, we examine the spinodal structures in (FeCoCrNi)85(AlCu)15 HEAs at different states using in-situ small-angle neutron scattering (SANS), in conjunction with transmission electron microscopy technique. The result demonstrates that SD occurred when aging the HEA samples at temperatures ranging from 500 to 800 °C, which leads to the phase constitution of NiAlCu-rich and FeCoCr-rich spinodal phases, L1₂ ordered phases, and FCC matrix. The characteristic wavelength of SD (${\lambda }_{\text{SD}}$) grows from 5.31 to 51.26 nm when aging temperature rises from 500 to 800 °C, which explains the enhancement of the alloy’s microhardness. The SD kinetics was unraveled by fitting the time-dependent ${\lambda }_{\text{SD}}$ through in-situ SANS measurement at 700 °C. During isothermal treatment at 700 °C, the ${\lambda }_{\text{SD}}$ increases from 10.42 to 17.43 nm with prolonged time, and SD is in the late stage from the exponential trend of the ${\lambda }_{\text{SD}}$ over time. Moreover, comparing with aging temperature, the aging time has a relatively minor impact on the coarsening of SD.

Key words: High entropy alloys, Spinodal decomposition, Small-angle neutron scattering, Kinetics

Shun-Fu Xie, Han-Qiu Jiang, Zhen-Hua Xie, Wei-Wen Zhang, Yu-Bin Ke. Unravel the Spinodal Decomposition Kinetics in (FeCoCrNi)85(AlCu)15 Alloy through Small-Angle Neutron Scattering[J]. Acta Metallurgica Sinica (English Letters), 2025, 38(1): 86-92.

Figures/Tables 8

Fig. 1 SANS curves of (AlCu)15 alloy at different states: a the in-situ 1D SANS curves during the heating process; b the ex-situ 1D SANS curves in the range of 500-800 °C

Table 1 The q0, I(q0), and λSD values at different aging temperatures

T (°C)	q₀ (Å⁻¹)	I(q₀) (cm⁻¹)	λ_SD (nm)
500	0.118	0.120	5.31
600	0.099	0.666	6.37
700	0.032	23.218	19.37
800	0.012	161.489	51.26

Fig. 2 (AlCu)15 alloy element distribution: a high-angle annular dark-field (HAADF) of 700 °C-6 h alloy and the corresponding EDX elemental maps, the images show the distribution for Fe, Co, Cr, Ni, Al, Cu compositions; b the distribution of elements corresponds to the red line in a

Fig. 3 In-situ SANS curves of (AlCu)15 alloy at 700 °C: a the in-situ 2D scattering curves, b the in-situ 1D scattering curves

Table 2 The q0, I(q0), and λSD values at 700 °C with increasing ageing period

t (h)	q₀ (Å⁻¹)	I(q₀) (cm⁻¹)	λ_SD (nm)
1	0.060	3.033	10.42
2	0.049	5.809	12.71
3	0.044	8.560	14.24
4	0.040	11.077	15.58
5	0.037	13.653	17.13
6	0.036	15.663	17.43

Fig. 4 Microstructures of the 700 °C-6 h alloy: a dark-field (DF) TEM image and corresponding selected area electron diffraction (SAED) pattern from [011] zone axis, b SAED pattern from [001] zone axis, and c the central dark field corresponding to L12 phase diffraction spot, d the high-angle annular dark-field scanning transmission electron microscopy (HADDF-STEM) image

Fig. 5 ${\lambda }_{\text{SD}}$ of the (AlCu)15 alloy evolves with time at 700 °C

Fig. 6 Microhardness of the (AlCu)15 alloy at different temperatures

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