Microstructural Characterization of Melt Extracted High-Nb-Containing TiAl-Based Fiber

Area of Science:

• Materials Science
• Metallurgical Engineering
• Solidification Science

Background:

• Titanium-aluminum-niobium (Ti-Al-Nb) alloys are critical in high-temperature applications.
• Understanding their microstructure is key to optimizing mechanical properties.
• Melt extraction is a method for producing alloy fibers with unique characteristics.

Purpose of the Study:

• To investigate the microstructure of melt extracted Ti-44Al-8Nb-0.2W-0.2B-1.5Si alloy fibers.
• To analyze the effect of rotation speed on fiber morphology.
• To identify the phases present and understand solidification behavior.

Main Methods:

• Melt extraction process at varying rotation speeds (2000-2600 r/min).
• Microstructural analysis using microscopy techniques.
• Phase identification through analysis of solidification reactions.

Main Results:

• Uniform wire appearance without defects at higher rotation speeds.
• Microstructure composed of fine alpha-2 (α) phase dendritic crystals.
• Precipitation of Ti₅Si₃ and TiB phases from eutectic reactions.
• Formation of divorced eutectic microstructure due to low Si content and high cooling rates.
• Observed segregation of Ti, Nb, B, Si, and Al during rapid solidification.

Conclusions:

• Melt extraction at optimized speeds yields defect-free Ti-Al-Nb alloy fibers.
• The alloy's microstructure is dominated by alpha-2 phase dendrites and eutectic phases (Ti₅Si₃, TiB).
• Rapid solidification and specific alloy composition lead to divorced eutectic structures and elemental segregation.