Tailoring a Refractory High Entropy Alloy by Powder Metallurgy Process Optimization.

Area of Science:

• Materials Science
• Metallurgy
• Alloy Development

Background:

• Refractory high-entropy alloys (RHEAs) offer superior high-temperature properties.
• Understanding microstructural evolution is crucial for optimizing RHEA performance.
• Low-density RHEAs are of interest for applications requiring reduced weight.

Purpose of the Study:

• To investigate the effect of milling time on the microstructure and mechanical properties of Al0.3NbTa0.8Ti1.5V0.2Zr RHEA.
• To determine optimal processing conditions for densification and property enhancement.
• To correlate processing parameters with resulting material characteristics.

Main Methods:

• Mechanical alloying and spark plasma sintering (SPS) were employed for alloy preparation.
• Powder characterization included morphology, chemical homogeneity, and crystal structure analysis.
• Microstructural analysis, hardness, and elastic constant measurements were performed on sintered samples.

Main Results:

• Milling time significantly influences contamination levels, with carbide formation observed after 3 hours and oxides after 30 hours.
• Ten hours of milling achieved a balance between microstructural homogeneity, refinement, high hardness, and minimal contamination.
• CALPHAD calculations were used to predict and compare phase changes with experimental observations.

Conclusions:

• Optimizing milling duration is critical for controlling contamination and achieving desired microstructural homogeneity in RHEAs.
• A 10-hour milling period provides a favorable balance for producing high-performance AlNbTaTiZr RHEAs.
• The study highlights the importance of feedstock powder processing on the final properties of spark plasma sintered RHEAs.