Effects of Subsequent Heat Treatment on Microstructure and High-Temperature Mechanical Properties of Laser 3D Printed GH4099 Alloy
ZHAO Yanan, GUO Qianying, LIU Chenxi, MA Zongqing(), LIU Yongchang
School of Materials Science and Engineering, Tianjin University, Tianjin 300072, China
Cite this article:
ZHAO Yanan, GUO Qianying, LIU Chenxi, MA Zongqing, LIU Yongchang. Effects of Subsequent Heat Treatment on Microstructure and High-Temperature Mechanical Properties of Laser 3D Printed GH4099 Alloy. Acta Metall Sin, 2025, 61(1): 165-176.
The multi-dimensional, multi-scale forming characteristics of laser powder bed fusion (LPBF) 3D printing technology, combined with its complex non-equilibrium solidification process, result in multilayered microstructures that differ significantly from those produced by traditional manufacturing methods. However, it is challenging to apply existing heat treatment solutions, developed for conventional manufacturing processes, to LPBF. Therefore, a tailored heat treatment approach is required for LPBF-printed components to regulate their microstructure and properties effectively. This study investigated the modulation mechanism of subsequent heat treatment on the non-equilibrium microstructure and high-temperature mechanical properties of 3D-printed GH4099 superalloy produced via LPBF. The findings reveal that solution treatment influences the recrystallization behavior of the printed microstructure and the precipitation behavior of carbides and γ' phases, which play critical roles in determining the alloy's high-temperature elongation. The multi-scale heterogeneous structure in the LPBF-fabricated GH4099 alloy enhances its microstructural thermal stability beyond that of conventional castings and forgings. Consequently, a high solution heat treatment temperature is necessary to achieve complete recrystallization. Following solution treatment at 1150 oC for 1.5 h, the columnar grains in the GH4099 prints were transformed into equiaxed grains, and large size twins were formed. Additionally, the precipitation of M23C6 carbides at the grain boundaries was suppressed. During subsequent aging heat treatment, the recrystallization induced by the solution treatment mitigated the distortion energy stored in the 3D-printed grains, thereby suppressing γ' phase precipitation in the matrix. As a result, by optimizing the heat treatment process, a favorable balance between high-temperature strength and plasticity was achieved in the GH4099 alloy.
Fund: National Natural Science Foundation of China(U22A20172);National Natural Science Foundation of China(52122409);National Key Research and Development Program of China(2023YFB3712002)
Corresponding Authors:
MA Zongqing, professor, Tel: 13702124121, E-mail: zqma@tju.edu.cn
Table 1 Heat treatment schemes of GH4099 alloy samples fabricated by laser powder bed fusion (LPBF)
Fig.1 Original microstructures of the GH4099 alloy sample fabricated by LPBF (a-c) and EDX line-scan analysis for the cell boundary (d) (a) OM image along building direction (b) SEM image of cells (c) TEM image of cells
Fig.2 Inverse pole figures (IPFs) of GH4099 alloy sample fabricated by LPBF (a) and after S1 (b) and S2 (c) solution heat treatments, and the variations in the size of grains as well as the hardness with solution heat treatment (d) (BD—build direction)
Fig.3 SEM images and EDX analysis results (insets) of grain boundary precipitation phases in the GH4099 alloy samples fabricated by LPBF after S1 (a) and S2 (b) solution treatments (w—mass fraction, a—atomic fraction)
Fig.4 Microstructures of γ' phase in the GH4099 alloy samples fabricated by LPBF after SA1-750 (a), SA1-800 (b), SA1-850 (c), and SA2-750 (d) heat treatments
Sample
d / nm
σb / MPa
δ / %
SA1-750
21 ± 5
498 ± 12
14.4 ± 3
SA1-800
33 ± 7
456 ± 8
15.2 ± 1
SA1-850
60 ± 10
390 ± 10
18.9 ± 4
SA2-750
15 ± 4
463 ± 7
29.7 ± 2
Table 2 γ' phase sizes and mechanical properties of the GH4099 alloy samples fabricated by LPBF after different heat treatments
Fig.5 DSC curves of GH4099 alloy samples fabricated by LPBF after different heat treatments
Fig.6 Grain orientation spread (GOS) maps (a, b), GOS value statistics (c, d), and grain misorientation angle fractions (e, f) in the GH4099 alloy samples fabriated by LPBF after S1 (a, c, e) and S2 (b, d, f) heat treatments (LAGB—low angle grain boundary, TB—twin boundary)
Fig.7 Stress-strain curves of GH4099 alloy samples fabricated by LPBF after different heat treatments tested at 900 oC (a) and comparisons of tensile properties at 900 oC between this work and those of LPBF fabricated nickel-based super-alloys reported in literatures [16,39,43-45] (b)
Fig.8 SEM images of the longitudinal (a, b) and transverse (c, d) sections of the fracture in GH4099 alloy samples fabricated by LPBF after SA1-750 (a, c) and SA2-750 (b, d) heat treatments (Insets in Figs.8a and b show the M23C6 carbides at grain boundary)
Fig.9 IPF (a) and kernel average misorientation (KAM) map (b) of SA2-750 treated sample after tensile at elevated temperature; TEM images representing the interaction between dislocations and M23C6 carbides at grain boundary (c) and the interaction between dislocation and γ' phase within grains (d) (Insets in Fig.9d show the high magnification TEM image and corresponding TEM dark field image)
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