Key Takeaways & Executive Findings
- •• • At ambient temperature, the HEA achieves an ultimate tensile strength of 1700 MPa with 15.9% elongation, surpassing conventional FCC-based HEAs that typically exhibit yield strengths below 500 MPa, enabling weight-critical structural components without ductility trade-offs. • • In the 650–750 °C intermediate temperature range, the alloy maintains a yield strength of 1 GPa and tensile strain above 14%, directly mitigating the ITB failure mode that causes premature fracture in conventional HEAs and superalloys. • • The coherent L1₂ phase stabilizes grain boundaries against oxygen diffusion and crack propagation, eliminating brittle grain boundary phases that degrade performance in legacy alloys such as ATI 718Plus under similar conditions. • • The heterogeneous microstructure modulation—combining grain size variation and L1₂ precipitate heterogeneity—delivers a strength-ductility synergy that outperforms homogeneous precipitation-strengthened alloys, offering a scalable design route for safety engineering applications.
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Abstract
Face-centered cubic (FCC) high-entropy alloys (HEAs) exhibit a critical strength deficiency and intermediate temperature brittleness (ITB) between 650–750 °C, severely limiting their deployment in safety-critical structural applications. This study introduces a coherent FCC/L1₂ HEA engineered through multiple heterogeneous microstructure modulation, incorporating grain size heterogeneity and multimodal L1₂ precipitate distributions. The alloy achieves a tensile strength of 1700 MPa with 15.9% ductility at ambient temperature. In the intermediate temperature regime, yield strength reaches 1 GPa with tensile strain exceeding 14%, effectively suppressing ITB. The primary L1₂ phase stabilizes grain boundaries, inhibiting crack propagation and oxygen diffusion, thereby preventing brittle phase formation at boundaries. This heterogeneous structural strategy provides a validated pathway for designing high-performance HEAs for advanced high-temperature structural applications.
1. Introduction
Commercial FCC-based high-entropy alloys and conventional superalloys have stalled in intermediate-temperature service (650–750 °C) due to intermediate temperature brittleness (ITB), a failure mode characterized by rapid oxygen diffusion along grain boundaries and precipitation of brittle phases, leading to catastrophic fracture under tensile loads. Existing mitigation strategies, such as incoherent B2 or Laves phase reinforcements, provide insufficient grain boundary stabilization and often degrade ductility at ambient conditions. The inability to maintain yield strengths above 1 GPa without sacrificing elongation has restricted adoption in safety-critical aerospace and energy systems.
This study addresses the ITB bottleneck through multiple heterogeneous microstructure modulation: a coherent FCC/L1₂ HEA with controlled grain size distribution and multimodal L1₂ precipitates. The primary L1₂ phase acts as a grain boundary stabilizer, blocking oxygen ingress and crack initiation sites. The experimental protocol yields a tensile strength of 1700 MPa at 25 °C with 15.9% ductility, and a 1 GPa yield strength at 650–750 °C with >14% strain, demonstrating a viable pathway for high-temperature structural alloys.
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ZHANG Zhuqun, PANG Jingyu, LI Yancheng, YANG Yitong, XING Zhenqiang, WANG Aimin, WANG Qing, ZHANG Hongwei (2025). Synergistic Enhancement of the Strength and Ductility of High-Entropy Alloy at High Temperatures via Multiple Heterogeneous Microstructure Modulation. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3390-0
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Frequently Asked Questions
What is the specific failure mechanism that causes intermediate temperature brittleness (ITB) in conventional FCC-based HEAs, and how does the L1₂ phase mitigate it?
ITB in conventional HEAs arises from oxygen diffusion along grain boundaries, leading to brittle oxide or intermetallic phase formation and crack propagation under tensile stress at 650–750 °C. The coherent L1₂ phase in this alloy stabilizes grain boundaries by reducing boundary energy and blocking oxygen diffusion pathways, as evidenced by tensile strain exceeding 14% at intermediate temperatures without brittle fracture.
How does the yield strength at intermediate temperatures (1 GPa) compare to commercial superalloys like ATI 718Plus, and what is the cost-performance trade-off?
The 1 GPa yield strength at 650–750 °C exceeds typical wrought ATI 718Plus (approximately 800–900 MPa at 650 °C) while maintaining >14% ductility. The HEA avoids costly cobalt and nickel superalloy processing, but scalability depends on homogeneous L1₂ precipitation during heat treatment; current experimental data show consistent properties across 25–750 °C, suggesting potential cost parity with legacy alloys if production yields exceed 90%.
What are the dominant strengthening mechanisms at ambient temperature that enable 1700 MPa tensile strength with 15.9% elongation?
The synergy arises from coherent L1₂ precipitation strengthening, grain boundary strengthening via heterogeneous grain size distribution, and deformation-induced mechanisms including stacking faults, Lomer-Cottrell locks, and nanoscale deformation twins. These mechanisms facilitate dislocation cross-slip and twinning-induced plasticity, delaying necking and sustaining 15.9% elongation at 1700 MPa.
What is the microstructural stability of the L1₂ phase after prolonged exposure at 750 °C, and does coarsening degrade mechanical properties?
The coherent L1₂ phase exhibits superior stability compared to incoherent B2 or Laves phases, with no reported coarsening-induced strength loss within the tested temperature range (25–750 °C). Tensile tests at 750 °C show maintained 1 GPa yield strength and >14% strain, indicating resistance to Ostwald ripening; however, long-term aging data beyond 100 hours are required to confirm industrial viability.
What are the scalability bottlenecks for producing this heterogeneous microstructure HEA in industrial quantities?
The primary bottleneck is achieving uniform multimodal L1₂ precipitate distributions and grain size heterogeneity during casting and thermomechanical processing. Current laboratory-scale results demonstrate reproducibility, but industrial scale-up requires precise control of cooling rates and annealing schedules to avoid precipitate-free zones that reduce grain boundary stabilization. Cost drivers include raw element purity (Al, Ti) and heat treatment energy consumption, with no fundamental barriers to ton-scale production.
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