Structural Stability of Titanium-Based High-Entropy Alloys Assessed Based on Changes in Grain Size and Hardness

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• High-entropy alloys (HEAs) offer unique properties due to their multi-element composition.
• Understanding the thermal stability of HEAs is crucial for their application in demanding environments.
• Powder metallurgy and advanced sintering techniques like U-FAST enable the fabrication of complex HEA structures.

Purpose of the Study:

• To analyze the thermal stability of the grain structure and mechanical properties of a TiCoCrFeMn high-entropy alloy.
• To investigate the effects of long-term annealing at 1000 °C on phase composition, grain size, and microhardness.
• To determine diffusion coefficients and confirm the sluggish diffusion phenomenon in HEAs.

Main Methods:

• Powder metallurgy using the U-FAST sintering method.
• Long-term annealing at 1000 °C in an argon atmosphere for up to 1000 hours.
• Microhardness measurements (Vickers method) and microstructural analysis (grain size assessment).

Main Results:

• The TiCoCrFeMn alloy reached structural stability after 100 hours of annealing.
• Stable grain sizes were approximately 2 µm (BCC) and 0.4 µm (BCC+C14).
• Annealing up to 1000 hours resulted in grain growth (2.7 µm and 0.7 µm) and a hardness decrease from 1065 HV to 1000 HV.

Conclusions:

• The TiCoCrFeMn alloy exhibits good structural stability up to 100 hours at 1000 °C.
• Long-term exposure leads to predictable microstructural evolution and property changes.
• The determined diffusion coefficients (D_Cr = 1.28 × 10^-19 m²·s^-1, D_Ti = 1.04 × 10^-19 m²·s^-1) confirm the sluggish diffusion characteristic of high-entropy alloys.