Formation and thermal stability of two-phase microstructures in Al-containing refractory compositionally complex...

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• Refractory Compositionally Complex Alloys (RCCA) exhibit complex microstructures.
• Phase separation mechanisms in RCCA, particularly spinodal decomposition versus nucleation and growth, are debated.
• Understanding these mechanisms is crucial for tailoring alloy properties.

Purpose of the Study:

• To definitively determine the phase separation mechanism in a specific Ta-Mo-Ti-Cr-Al alloy.
• To investigate the kinetics of phase separation under various annealing conditions.
• To correlate microstructure evolution with alloy hardness.

Main Methods:

• Utilized atom probe tomography and electron microscopy.
• Annealed samples over a wide range of times (orders of magnitude).
• Analyzed microstructural evolution and chemical composition at phase interfaces.

Main Results:

• Confirmed phase separation occurs through nucleation and growth, not spinodal decomposition.
• Observed initial formation of 2 nm ordered clusters upon quenching.
• Microstructure coarsened but precipitates remained <100 nm even after 1000 h annealing.
• Sharp interfaces with no significant chemical transition were observed.

Conclusions:

• The phase separation mechanism in this RCCA is unequivocally nucleation and growth.
• The findings contrast with spinodal decomposition hypotheses for other RCCA systems.
• The study provides insights into precipitation and coarsening effects on alloy hardness.