Grain-Size-Dependent Hall-Petch Relationship in CoCrFeTiNi_2.1 High-Entropy Alloys

Area of Science:

• Materials Science
• Computational Materials Science
• Alloy Design

Background:

• High-entropy alloys (HEAs) exhibit unique mechanical properties due to their complex solid-solution structures.
• Understanding the interplay between microstructure, temperature, and strain rate is crucial for designing advanced HEAs.
• Nanocrystalline materials often display size-dependent mechanical behaviors, including inverse Hall-Petch effects.

Purpose of the Study:

• To investigate the size-dependent mechanical behavior of CoCrFeTiNi2.1 high-entropy alloys using molecular dynamics simulations.
• To explore the influence of temperature and strain rate on the alloy's mechanical response.
• To elucidate the atomistic mechanisms governing the structure-property relationships in nanocrystalline HEAs.

Main Methods:

• Atomistic simulations using molecular dynamics (MD).
• Systematic variation of grain size (6-18 nm), temperature (300-1200 K), and strain rate (4 × 10^10–10 × 10^10 s^-1).
• Analysis of tensile strength, flow stress, phase transformations, and dislocation dynamics.

Main Results:

• A transition from inverse Hall-Petch (IHP) to classical Hall-Petch (HP) behavior was observed at a critical grain size of 12 nm.
• Maximum tensile strength and flow stress were achieved at the critical grain size of 12 nm.
• Elevated temperatures reduced strength by 15.67% due to phase depletion and reduced dislocation density.
• Increased strain rate enhanced strength by 18.12% via BCC/HCP transformations and dislocation proliferation.

Conclusions:

• The study establishes a clear "structure-temperature/strain rate-property" linkage in the CoCrFeTiNi2.1 HEA.
• An atomistic understanding of grain size effects under thermal and kinetic loading is provided.
• Findings offer mechanistic insights for designing nanocrystalline HEAs with tailored mechanical performance.