Key Takeaways & Executive Findings
- •• A novel Ni-based superalloy with 0.1 wt.% graphene nanosheets (GNs) exhibits a 31 HV increase in hardness and 86 MPa increase in yield strength compared to the base alloy, due to synergistic strengthening from in-situ formed nano-carbides and residual GNs. • The in-situ reaction of GNs with alloy melt during laser powder bed fusion generates uniformly dispersed nano-carbides that refine the cellular structure and hinder dislocation movement, enhancing mechanical properties. • The study demonstrates the potential of using graphene as a strengthening agent in additive manufacturing, offering a promising alternative to conventional refractory element addition for high-performance superalloys. • The combination of SEM, EBSD, TEM, DSC, and SANS provides comprehensive microstructural and thermophysical characterization, confirming the presence and distribution of nano-carbides and residual GNs.
Abstract
With the increase in power of the industrial gas turbine and thrust-weight ratio of aeroengine, the conventional strengthening method of adding refractory elements into superalloys has become difficult to meet the demands for the higher mechanical properties. A novel Ni-based superalloy was designed with enhanced strength and hardness based on the graphene nanosheets (GNs) synergistic in-situ nano-carbides strengthening in the present work. Nano-carbides were induced by in-situ reaction of the GNs with alloy powders during additive manufacturing. The microstructure and thermophysical properties of different alloys with 0.1wt.% GNs and without GNs were investigated by SEM, EBSD, TEM, differential scanning calorimetry (DSC), and small angle neutron scattering (SANS). Residual GNs were also detected by SANS and DSC. The nano-carbides are uniformly distributed in the matrix and combine with residual GNs to refine the cellular structure. Compared with the original alloy (ASE100), the hardness of the alloy with 0.1wt.% GNs (ASE100-0.1GN) is increased by 31 HV (from 315 HV to 346 HV), and the yield tensile strength is increased by 86 MPa (from 756 MPa to 842 MPa). The GNs react with alloy melt in the molten pools to generate nano-carbides under the Marangoni effect during manufacturing process. The dispersion nano-carbides are distributed at both grain boundaries and within grains, effectively hindering the movement of dislocation and enhancing the strength of alloy.
1. Introduction
As the power of industry gas turbines and thrust-weight ratio of aeroengines continue to increase, superalloys with higher mechanical properties and microstructure stability are required [1,2]. The typical strengthening methods in superalloys contain solid solution strengthening and precipitation strengthening, which rely on the addition of refractory elements and the introduction of nano-precipitates. Recently, more attention has been paid to the strengthening method by introducing nanoparticles in superalloys, instead of the traditional strategy of adding more refractory elements [3,4].
As classical nanoparticles, TiC carbides have a wide range of applications in the field of superalloys in recent years [5-10]. Jiang et al. [11] introduced 0.02wt.% TiC nanoparticles into the K214 superalloy melt and fabricated the strengthened alloy by vacuum induction melting. Finer grains, coarse secondary dendrite arms, and lower micro-segregation were obtained. The ultimate tensile strength and elongation of the strengthened alloy at room temperature increased from 966 MPa and 1.5% to 1,060 MPa and 2.8%, respectively. Furthermore, Huang et al. [9] placed the Ni-Cr-W Ni-based superalloy ingots and the TiC nanoparticles package in the melting crucible of the vacuum induction melting furnace to prepare the strengthened alloy. The TiC nanoparticles mainly acted as nucleation sites for MC-type carbides and accelerated the precipitation of MC carbides, which refines the carbides and enhances the high temperature strength [9]. However, it remains challenging to control the size and distribution of TiC nanoparticles when directly introduced into the melt. Recent studies are focused on addressing this critical issue by utilizing more advanced fabrication processes or designing an effective introduction method.
Laser powder bed fusion (LPBF) is an additive manufacturing (AM) technique used for fabricating alloy components with complex geometry and internal structure [12-19]. High melt cooling rates and great temperature gradient achieved by fast laser scanning in LPBF provide a solution to the coarsening and inhomogeneous distribution of the nanoparticles [10, 20-23]. Taheri et al. [24] demonstrated that TiC nanoparticles can act as heterogeneous nucleation sites during solidification of superalloy. This refined the grains, thus reducing the strain concentration and inhibiting the cracks in GTD-111 superalloy fabricated by LPBF. Furthermore, the TiC nanoparticles were also reported to refine the grains and reduce local strain concentration in the LPBF CM247LC superalloy [25]. The uniform distribution of TiC nanoparticles can
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Shi-ling Min, Li Wang, Jia-sheng Li, Jing Liu, Dong-yan Liu, Xiang-wei Li, Zhong Chen, Jia-sheng Dong, Lang-hong Lou (2025). Ni-based superalloy synergistic strengthened by in-situ nano-carbides and residual graphene fabricated via laser powder bed fusion. China Foundry. https://doi.org/10.1007/s41230-025-5161-3
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Frequently Asked Questions
What is the main innovation of this research?
The research introduces a novel Ni-based superalloy strengthened by graphene nanosheets (GNs) that react in-situ to form nano-carbides during laser powder bed fusion, achieving synergistic strengthening and improved mechanical properties.
How does the addition of graphene nanosheets improve the superalloy's properties?
The addition of 0.1 wt.% GNs leads to the formation of uniformly distributed nano-carbides and residual GNs, which refine the cellular structure and hinder dislocation movement, resulting in increased hardness (by 31 HV) and yield strength (by 86 MPa).
What characterization techniques were used in this study?
The study employed SEM, EBSD, TEM, differential scanning calorimetry (DSC), and small angle neutron scattering (SANS) to investigate the microstructure and thermophysical properties of the alloys.
What is the significance of using laser powder bed fusion (LPBF) in this context?
LPBF provides high cooling rates and large temperature gradients that help achieve uniform distribution of nanoparticles and prevent coarsening, addressing challenges in controlling nanoparticle dispersion in superalloys.
What are the potential applications of this strengthened superalloy?
The enhanced mechanical properties make this superalloy suitable for high-temperature applications in industrial gas turbines and aeroengines, where improved strength and stability are critical.
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