Thermally Stable Heterogeneous-Grained Refractory High-Entropy Alloy Offering Superior Strength from 77 to 973 K

Area of Science:

• Materials Science
• Metallurgy
• Mechanical Engineering

Background:

• Refractory high-entropy alloys (RHEAs) face challenges in balancing strength and ductility over wide temperature ranges.
• Developing RHEAs with consistent mechanical properties from cryogenic to high temperatures is crucial for advanced applications.

Purpose of the Study:

• To design a cold-workable NbTaTiHf-based RHEA with a thermally stable heterogeneous grain structure.
• To achieve a robust strength-ductility balance in RHEAs across a broad temperature spectrum (77 K to 973 K).

Main Methods:

• Thermomechanical processing was employed to create a tailored, thermally stable heterogeneous grain structure.
• Mechanical testing was conducted at temperatures ranging from 77 K to 973 K to evaluate tensile strength and ductility.

Main Results:

• The designed RHEA demonstrated exceptional mechanical performance, with tensile strengths exceeding 1.8 GPa at 77 K and over 900 MPa at 973 K.
• The heterogeneous microstructure remained thermally stable at high temperatures due to concentrated refractory elements and sluggish kinetics.
• Hetero-deformation-induced (HDI) strengthening mechanisms were effectively maintained across all tested temperature regimes.

Conclusions:

• A practical design strategy for next-generation RHEAs with superior, wide-temperature mechanical properties was established.
• The thermally stable heterogeneous microstructure is key to achieving robust strength-ductility balance in RHEAs.
• This research provides a pathway for developing advanced RHEAs for demanding environments.