Key Takeaways & Executive Findings
- •• • The optimized (CoCrNi)90Mo10 MEA with regulated partial recrystallization achieves a wear rate at 113 K that is less than half of its as-cast and fully recrystallized counterparts, demonstrating a significant improvement in cryogenic wear resistance. • • The engineered microstructure comprises a fully recrystallized FCC phase embedded within a continuous skeleton of hard, non-recrystallized σ phase, providing a synergistic combination of structural support and strain accommodation. • • The σ skeleton distributes stress deeply, while the recrystallized FCC phase, with its high density of grain boundaries and annealing twins, suppresses interfacial cracking, addressing the fundamental trade-off between strength and damage tolerance. • • This microstructural design strategy offers a practical pathway for developing high-performance, crack-resistant dual-phase composites for extreme cryogenic environments, overcoming the limitations of conventional second-phase strengthening.
Abstract
The pursuit of advanced wear-resistant materials for cryogenic applications is often hindered by a fundamental trade-off between enhancing strength and damage tolerance. CoCrNi-based medium-entropy alloys (MEAs), while excellent in cryogenic toughness, suffer from this very limitation. Although second-phase reinforcement boosts strength, the strain incompatibility between phases inevitably triggers cracking, which is severely exacerbated at low temperatures. This work introduces a novel microstructural design strategy based on regulated partial recrystallization to overcome this long-standing challenge. By tailoring the thermomechanical processing of a (CoCrNi)90Mo10 MEA, we engineered a unique architecture where a fully recrystallized FCC phase is homogeneously embedded within a continuous skeleton of a hard, non-recrystallized σ phase. The alloy with this optimized microstructure achieved a remarkably low wear rate at 113 K that is less than half of its as-cast and fully recrystallized counterparts. The experimental and modeling results indicate the underlying synergy: the σ skeleton provides robust structural support and distributes stress deeply, while the recrystallized FCC phase, with its high density of grain boundaries and annealing twins, acts as a compliant strain-accommodating medium, effectively suppressing interfacial cracking. This combined 'skeleton effect' and 'recrystallization effect' not only delivers exceptional cryogenic wear resistance but also offers a practical strategy for designing high-performance, crack-resistant dual-phase composites for extreme environments.
1. Introduction
CoCrNi medium-entropy alloys (MEAs) are recognized for their superior cryogenic mechanical properties, including strength-ductility balance, high strain hardening rate, toughness, and damage tolerance. However, their wear resistance at cryogenic temperatures remains limited, posing a significant bottleneck for engineering applications. Conventional lubrication methods often fail under cryogenic conditions, subjecting moving components to harsh dry sliding wear, which exacerbates the wear challenge.
Second-phase strengthening has been widely applied to enhance the yield strength and wear behavior of CoCrNi-based alloys. Mo-doped CoCrNi MEAs exhibit significantly improved mechanical properties due to the introduction of the σ phase. However, damage nucleation can occur within this hard yet brittle phase, and inconsistent strain distribution between phases serves as a source of crack initiation, particularly at low temperatures. This work introduces a novel microstructural design strategy based on regulated partial recrystallization to overcome this trade-off, achieving exceptional cryogenic wear resistance by engineering a dual-phase architecture that synergistically combines a hard σ skeleton with a compliant recrystallized FCC phase.
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Yue Ren, Longhui Zhu, Yusen Li, Qing Zhou, Stefan J. Eder, Xudong Sui, Qingfeng Wu, Haifeng Wang, Zhijun Wang, Carsten Gachot, Jian Wang, Weimin Liu (2026). Cryogenic Tribological Breakthroughs in Medium-Entropy Alloy Composites via Regulated Partial Recrystallization. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-4018-6
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Frequently Asked Questions
What is the specific wear rate improvement achieved at 113 K compared to as-cast and fully recrystallized counterparts?
The optimized alloy achieved a wear rate at 113 K that is less than half of its as-cast and fully recrystallized counterparts, indicating a substantial enhancement in cryogenic wear resistance.
How does the regulated partial recrystallization strategy mitigate interfacial cracking in dual-phase composites?
The strategy creates a microstructure where a fully recrystallized FCC phase is embedded within a continuous skeleton of hard, non-recrystallized σ phase. The σ skeleton provides robust structural support and distributes stress deeply, while the recrystallized FCC phase, with its high density of grain boundaries and annealing twins, acts as a compliant strain-accommodating medium, effectively suppressing interfacial cracking.
What are the underlying mechanisms responsible for the enhanced cryogenic wear resistance?
The enhanced wear resistance is attributed to the combined 'skeleton effect' and 'recrystallization effect'. The σ skeleton offers structural support and deep stress distribution, while the recrystallized FCC phase accommodates strain and prevents crack propagation, leading to reduced wear.
What is the significance of the (CoCrNi)90Mo10 composition in this study?
The Mo addition promotes the formation of the hard σ phase, which is essential for the dual-phase architecture. The specific composition (CoCrNi)90Mo10 was tailored to achieve the desired balance between the recrystallized FCC matrix and the σ skeleton, enabling the observed improvements.
How does this approach compare to conventional second-phase strengthening in terms of damage tolerance?
Conventional second-phase strengthening often leads to strain incompatibility and cracking at phase boundaries, especially at low temperatures. The regulated partial recrystallization approach overcomes this by embedding a compliant recrystallized FCC phase within the hard skeleton, which accommodates strain and suppresses cracking, thereby improving damage tolerance and wear resistance.
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