Microstructure and Phase Equilibria in BCC-B2 Nb-Ti-Ru Refractory Superalloys.

Area of Science:

• Materials Science
• Metallurgy
• High-Temperature Materials

Background:

• Refractory superalloys (RSAs) are critical for high-temperature, high-strength applications.
• Two-phase RSAs, particularly those with body-centered cubic (BCC) and ordered B2 phases, are highly promising.
• Ruthenium (Ru)-based B2 precipitates offer stable microstructures above 1600 °C.

Purpose of the Study:

• To experimentally investigate the Nb-Ti-Ru ternary system as a foundational system for RSAs.
• To determine phase equilibria and properties of specific Nb-Ti-Ru alloys at elevated temperatures.
• To provide data for the development of RSAs with Ru-based B2 strengthening precipitates.

Main Methods:

• Experimental investigation of two Nb-Ti-Ru alloys: (Nb3Ti)0.85Ru0.15 and (Nb4Ti)0.85Ru0.15.
• Phase equilibria and property determination across a temperature range of 900 °C to 1300 °C.
• Analysis of elemental distribution and phase composition within the BCC and B2 phases.

Main Results:

• The B2 phase exhibited strong RuTi ordering with significant Niobium (Nb) solubility (up to 18 mol%).
• The Nb-rich BCC matrix incorporated substantial amounts of Ru (up to 15 mol%) and Titanium (Ti) (up to 20 mol%).
• A two-phase microstructure (B2 precipitates in BCC matrix) was confirmed, but with a larger-than-anticipated lattice misfit.

Conclusions:

• The Nb-Ti-Ru system provides valuable insights into phase formation for refractory superalloys.
• Understanding elemental partitioning and lattice misfit is crucial for optimizing RSA performance.
• This research supports the design of next-generation RSAs leveraging Ru-based B2 precipitates.