Key Takeaways & Executive Findings
- •• A novel FeCrNiAl0.1Si0.1 medium entropy alloy achieves exceptional strength-ductility synergy at intermediate temperatures (873 K) with yield strength of 693.83 MPa, ultimate tensile strength of 817.55 MPa, and uniform elongation of 18.27%. • Heterogeneous precipitation of micron-scale σ phase at grain boundaries and nanoscale B2 phase within grains enables simultaneous strengthening and toughening across a wide temperature range. • The alloy exhibits excellent cryogenic and ambient temperature mechanical properties due to dislocation shearing of B2 phases, Orowan bypass of σ phase, and high density of nano-twins and stacking faults. • The study provides a new strategy for developing precipitation-hardened Fe-Cr-Ni austenitic alloys for high-temperature applications in nuclear and aerospace industries.
Abstract
Fe–Cr–Ni austenitic alloys are extensively utilized in the hot-end components of nuclear light water reactors, turbine disks, and gas compressors. However, their low strength at elevated temperatures limits their engineering applications. In this study, a novel precipitation-strengthened alloy system is developed by incorporating Al and Si elements into a FeCrNi equiatomic alloy. The results indicate that the FeCrNiAlxSix (at%, x = 0.1, 0.2) alloys possess heterogeneous precipitation structures that feature a micron-scale σ phase at the grain boundaries and a nanoscale ordered body-centered cube (B2) phase within the grains. An exceptional strength–ductility synergy across a wide temperature range is achieved in FeCrNiAl0.1Si0.1 alloys due to grain refinement and precipitation strengthening. Notably, a yield strength of 693.83 MPa, an ultimate tensile strength of 817.55 MPa, and a uniform elongation of 18.27% are attained at 873 K. The dislocation shearing mechanism for B2 phases and the Orowan bypass mechanism for σ phase, coupled with a high density of nano-twins and stacking faults in the matrix, contribute to the excellent mechanical properties at cryogenic and ambient temperatures. Moreover, the emergence of serrated σ phase and micro-twins in the matrix plays a crucial role in the strengthening and toughening mechanisms at intermediate temperatures. This study offers a novel perspective and strategy for the development of precipitation-hardened Fe–Cr–Ni austenitic alloys with exceptional strength–ductility synergy over a broad temperature range.
1. Introduction
The search for materials with excellent mechanical properties across a wide temperature range has been a long-term goal of the materials community. Alloys with high contents of chromium (Cr), iron (Fe), and nickel (Ni) have served as engineering heat-resistant materials for over a century, primarily in the core components of nuclear light water reactors, turbine disks, and gas compressors [1–2]. The mechanical properties of these heat-resistant materials are notably affected by service temperature, posing a considerable challenge in achieving an optimal strength–toughness synergy across a wide temperature spectrum. The development of medium- and high-entropy alloys (M/HEAs) has recently introduced an innovative approach that differs from traditional alloy design [3–7]. Reports indicate that single-phase face-centered cubic (FCC) M/HEAs exhibit excellent low-temperature mechanical properties, even at 4.2 K [8], and possess the best cryogenic fracture toughness reported to date [9–12].
Numerous studies have demonstrated that nearly all single-phase FCC M/HEAs exhibit a remarkable reduction in strength at elevated temperatures [13–16]. A single-phase matrix must be strengthened by second phases and precipitates to maintain high strength [17–20]. Precipitation-reinforced microstructures are extensively employed in high-temperature materials, such as Ni–Fe-based superalloys and heat-resistant steels, where a single FCC matrix is strengthened by the L12 phase and carbides [17–21]. The primary constituent elements of these alloys are Cr, Fe, and Ni, while other solid solution elements such as V, Ti, and Nb promote the precipitation of brittle carbides, enhancing the mechanical properties of heat-resistant steel at elevated temperatures [21–22]. However, the presence of carbides within the matrix can lead to notable strain softening due to severe interface cracking during deformation at high temperatures [22], a phenomenon similar to that observed in particle-reinforced composites [23]. Additionally, the ordered L12 phase, commonly utilized in superalloys, exhibits considerable embrittlement in the intermediate temperature range, although the underlying reasons for this remain controversial [17,21]. Consequently, reinstating the NiAl-B2 phase, which was previously considered a potential high-temperature phase for high-temperature alloys, is crucial. The B2 phase features an ordered body-centered cubic (BCC) structure that has been extensively studied and introduced as a precipitating phase to enhance the mechanical properties of alloys.
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Tianxiang Bai, Tuanwei Zhang, Zhiming Jiao, Jinyao Ma, Hui Chang, Jianjun Wang, Dan Zhao, Shengguo Ma, Zhouzhu Mao, Xiaoxiao Liu, Zhihua Wang (2025). Achieving the excellent intermediate-temperature strength–ductility synergy in a fine-grained FeCrNi-based medium entropy alloy with heterogeneous precipitation. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-3034-1
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Frequently Asked Questions
What is the main achievement of this study?
The study develops a novel FeCrNiAl0.1Si0.1 medium entropy alloy that achieves excellent strength-ductility synergy at intermediate temperatures, with yield strength of 693.83 MPa, ultimate tensile strength of 817.55 MPa, and uniform elongation of 18.27% at 873 K.
What are the key microstructural features contributing to the improved properties?
The alloy exhibits heterogeneous precipitation with micron-scale σ phase at grain boundaries and nanoscale B2 phase within grains, along with high density of nano-twins and stacking faults, which together enhance strength and ductility.
How does the alloy perform at cryogenic and ambient temperatures?
At cryogenic and ambient temperatures, the alloy shows excellent mechanical properties due to dislocation shearing of B2 phases and Orowan bypass of σ phase, coupled with nano-twins and stacking faults.
What is the significance of this research for engineering applications?
This research provides a new strategy for developing precipitation-hardened Fe-Cr-Ni austenitic alloys with exceptional strength-ductility synergy over a broad temperature range, which is crucial for hot-end components in nuclear reactors, turbines, and gas compressors.
What are the mechanisms responsible for strengthening at intermediate temperatures?
At intermediate temperatures, the emergence of serrated σ phase and micro-twins in the matrix plays a crucial role in strengthening and toughening mechanisms.
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