Key Takeaways & Executive Findings
- •• A novel non-equiatomic Fe27Ni27Co26Cu10Ti10 HEA was developed, achieving a fcc+η structure after heat treatment, with total elongation improved from ~0.9% to 7.5%. • The needle-like η-D024 phase, often considered deleterious, was shown to provide effective precipitation strengthening while maintaining ductility, expanding reinforcing phase options for fcc HEAs. • The enhanced ductility is attributed to the strong hindering effect of needle-like η phase at grain boundaries, restricting crack propagation and dislocation movement. • This study provides valuable insights into phase transformation and the strengthening effect of the η-D024 phase, guiding future alloy design for strength-ductility synergy.
Abstract
Precipitation strengthening is an effective strengthening strategy widely utilized in high-entropy alloys (HEAs) with a single-phased face-centered cubic (fcc) structure. In recent research works, reinforcing phase adopted are mostly focused on equiaxed or nearly equiaxed structures (e.g., spherical, cubic, and rod-like), while relatively rare studies on the strengthening effects of needle-like precipitates with large aspect ratios. The η-D024 phase, like the L12 strengthening phase most commonly used in fcc-structured HEAs, features an ordered Ni3Ti-type structure and also exhibits a comparable strengthening effect. However, since the η phase often co-precipitates with other precipitates in alloy system, the strengthening effect of the sole η-D024 phase in fcc-structured alloys remains to be further explored. In this study, microstructural evolution, phase transformation, and mechanical behaviors of a non-equiatomic Fe27Ni27Co26Cu10Ti10 HEA were systematically investigated. Results show that following high-temperature heat treatment, the microstructure of the studied HEA transforms from a combination of the fcc, L12, Cu-rich, and η phases in the as-cast state to a fcc+η structure in the heat-treated state. Meanwhile, the mechanical properties of the heat-treated HEA are significantly improved, with a total elongation increasing from approximately 0.9% to 7.5%. The enhanced ductility of the heat-treated alloy can be attributed to the strong hindering effect of numerous needle-like η phase at the grain boundaries, which restricts crack propagation and dislocation movement. This study develops a novel η-strengthened FeNiCoCuTi HEA, expanding the selection of available reinforcing phases in fcc-structured alloys and providing valuable insights into the phase transformation and strengthening effect of the η-D024 phase.
1. Introduction
High-entropy alloys (HEAs) or multi-principal-element alloys (MPEAs) with various excellent properties and unique characteristics have become one of the hot research topics in metal materials [1, 2]. Face-centered cubic (fcc) structured HEAs are particularly notable for their high ductility, outstanding impact toughness, attractive strain hardening capacity, and good corrosion resistance [3-5]. However, due to the inherent feature of the crystal structure, the yield strength of fcc-structured HEAs, especially polycrystalline HEAs, is usually unsatisfactory, making it challenging to meet industrial demands [6, 7]. Plentiful studies have focused on improving the moderate strength of the fcc-structured HEAs, with commonly used strengthening strategies including solid solution strengthening, grain refinement strengthening, precipitation strengthening, and heterogeneous strengthening [8-11].
Precipitation strengthening stands out among multiple strengthening mechanisms by its remarkable strengthening effect and adjustable performance, achievable through simplified alloying and heat treatment processes [12, 13]. Numerous reinforcing phases can be introduced into single-phase fcc matrix, including ordered fcc-structured L12, disordered body-centered cubic (bcc), ordered bcc-structured B2, topological closed packed (tcp) structured σ, μ, and Laves, ordered hexagonal close-packed (hcp) structured η-D024, and so on [14-18]. Among them, ordered L12 phase is the most widely used strengthening phase in fcc-structured HEAs, which can significantly improve strength without a substantial loss in ductility [19, 20]. For instance, Yang et al. [14] reported a L12-strengthened Ni-30Co-13Fe-15Cr-6Al-6Ti-0.1B HEA by duplex-aging treatment, achieving a remarkable improvement of strength and ductility. Conversely, the ordered η-D024 phase, which shares the same Ni3Ti-type structure as the L12 phase, is generally considered deleterious in fcc-structured alloys [21]. In fact, the η-D024 phase with proper distribution and volume fraction can also enhance strength under the premise of limited ductility reduction [22]. The morphologies of L12 or B2 phases typically exhibit equiaxed or near-equiaxed characteristics (e.g., spherical, cubic, and rod-like), whereas needle-like η phase, distinctively, has a significantly larger aspect ratio with pronounced anisotropy. This morphological difference results in needle-like η phase having a stronger ability to impede dislocation movement than L12 or B2 phases, leading to a superior strengthening effect. Since the η-D024 phase typically occurs in conjunction with other precipitates, its sole strengthening effect remains to be explored.
Loading authentic research manuscript (Pages 1–5)...
Li-ran Huang, Zhi-ming Li, Wei-ping Chen, Zhi-qiang Fu (2026). Tuning needle-like precipitation for enhanced strength-ductility synergy in a non-equiatomic FeNiCoCuTi high-entropy alloy. China Foundry. https://doi.org/10.1007/s41230-025-5127-5
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the main finding of this study?
The study demonstrates that a non-equiatomic Fe27Ni27Co26Cu10Ti10 high-entropy alloy can be strengthened by needle-like η-D024 precipitates, achieving a significant improvement in ductility (from ~0.9% to 7.5% total elongation) while maintaining strength, contrary to the common belief that η phase is detrimental.
How does the η-D024 phase contribute to strengthening?
The needle-like morphology of η-D024 phase with large aspect ratio provides a stronger hindrance to dislocation movement compared to equiaxed precipitates like L12 or B2, thereby enhancing strength. Additionally, the η phase at grain boundaries restricts crack propagation, improving ductility.
What is the novelty of this research?
This research is novel because it focuses on the strengthening effect of the sole η-D024 phase in fcc-structured high-entropy alloys, which has been rarely studied. It also develops a new alloy composition and heat treatment route to achieve a fcc+η microstructure with enhanced strength-ductility synergy.
What are the potential applications of this alloy?
The developed FeNiCoCuTi high-entropy alloy with enhanced strength and ductility could be used in structural applications requiring high performance, such as aerospace components, automotive parts, and other engineering applications where both strength and ductility are critical.
What is the significance of this study for the field of high-entropy alloys?
This study expands the selection of reinforcing phases in fcc-structured high-entropy alloys by demonstrating that η-D024 phase can be effectively used for precipitation strengthening. It provides insights into phase transformation and strengthening mechanisms, guiding future alloy design for improved mechanical properties.
Related Technical Papers & Translations
Pull-out capacity and energy absorption of cable bolts under impact loading
This study investigates the performance of high-strength cable bolts under impact loading conditions representative of rock bursts in underground environments. Although widely used, the dynamic behaviour of these cable bolts has received limited experimental attention, and their effectiveness in seismically active zones remains a subject of ongoing debate. To address this gap, a reverse pull-out test machine integrated with a drop hammer rig was employed. Tests were conducted on 70-t SUMO bulbed and non-bulbed cable bolts with encapsulation lengths of 300 and 450 mm, subjected to an impact energy of 14.52 kJ. Results indicate that non-bulbed cables, despite showing lower initial peak loads (average 218 vs. 328 kN for bulbed cables at 300 mm encapsulation), demonstrated superior energy absorption (average 11.26 vs. 8.75 kJ) and displacement capacity (average 48.40 vs. 36.25 mm). Increasing the encapsulation length for bulbed cables led to a reduction in initial peak load but improved displacement and energy absorption. The dominant failure mechanism was debonding at the cable-grout interface, characterised by frictional sliding and cable rotation. These findings provide new insights into the energy dissipation mechanisms of cables and support the development of more resilient ground support systems for dynamically active conditions.
Effect of eutectic content on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys
The 7xxx series aluminum alloys have emerged as a particularly promising class of lightweight structural materials. However, the inherent strength of these materials is primarily influenced by the content and type of alloying elements added during the manufacturing process, as well as casting defects. The present study investigated the effects of eutectics formed by solute atoms (Zn, Mg, and Cu), with equal mass ratios (Zn/Mg=2, Mg/Cu=3) but varying overall contents, on the liquid film thickness, crack propagation depth, and the mechanical properties of the Al-Zn-Mg-Cu alloy after heat treatment. The results from gravity casting indicate that the intergranular liquid film thickness increases with the increase of eutectic content. A thick intergranular liquid film in the casting can accommodate greater strain during grain contraction, thereby preventing liquid film rupture and subsequent hot tearing. Concurrently, during the solution treatment at 475 °C, the residual eutectic fraction in the Al-7Zn-3.5Mg-1.18Cu alloy diminishes from 9.1% at 10 h to 0.35% at 40 h. At 165 °C, the Al-6Zn-3.0Mg-1.0Cu alloy exhibits the optimal mechanical properties, with a peak aging tensile strength of 510 MPa and an elongation of 6.4%. The incorporation of lower concentrations of solute atoms (Zn, Mg, and Cu) serves to reduce the barrier to dislocation precipitation, thereby enhancing alloy plasticity. However, when the proportion of alloying elements exceeds the solubility limit of the α-Al matrix at specific heat treatment temperatures, coarse residual phases remain intergranular, thereby significantly impairing the mechanical properties of the alloy. This study provides a reference for the optimal addition level of the main strengthening elements in Al‑Zn‑Mg‑Cu alloys.
Achieving optimal strength-conductivity balance in cast Al-2.3Fe-Mg-Si alloys via Mg/Si ratio regulation
The Al-2.3Fe eutectic alloy is regarded as a promising substitute for Cu conductors in automotive motors owing to its excellent castability and low resistivity. However, its application is restricted by the mutually exclusive relationship between electrical conductivity and mechanical strength. The microstructure and mechanical properties of Al-2.3Fe alloy were modified through Mg/Si alloying combined with T6 heat treatment in this work, leading to the development of a high-performance cast Al-2.3Fe-Mg-Si alloy. In the Al-2.3Fe-0.40Mg-0.72Si (Mg/Si=0.56) alloy subjected to T6 treatment, an electrical conductivity of (52.5±0.6)% IACS is achieved, while the ultimate tensile strength is significantly enhanced to 309.5±5.6 MPa. The addition of Mg and Si brings about marked changes in the solidification process of the Al-2.3Fe alloy, resulting in considerable variations in both the morphology of the second phase and its phase constitution. The aging behavior of the alloy is governed by second phase and solid solubility. Through optimization of the Mg/Si ratio, the aging response can be effectively enhanced. At the ratio of Mg/Si=0.56, a balance is achieved between solid solubility and precipitation, while simultaneously minimizing the detrimental impact on electrical conductivity and reaching the best mechanical properties and electrical conductivity in peak-aged Al-2.3Fe-xMg-ySi alloy. This work providing valuable insights for developing advanced conductor materials.