Microstructural Characterization of Defects and Secondary Phases in (Ti, Ta)C-Type Carbides in Nickel-Based...

Area of Science:

• Materials Science
• Metallurgy
• Nanotechnology

Background:

• Metal carbides (MCs) are crucial strengthening phases in nickel-based superalloys.
• Decomposition of MCs during high-temperature creep degrades alloy properties and lifespan.
• Microscale investigations into MC decomposition mechanisms are limited.

Purpose of the Study:

• To investigate the microstructural characteristics of metal carbides (MCs) in nickel-based superalloys.
• To explore the relationship between microstructural defects and MC decomposition.
• To enhance the fundamental understanding of carbide behavior and interactions within superalloys.

Main Methods:

• Aberration-corrected scanning transmission electron microscopy (STEM) was used for high-resolution microstructural characterization.
• Detailed microstructural analysis of MCs (Ti, Ta) in a nickel-based superalloy.
• Identification and characterization of stacking faults and secondary precipitates within MCs.

Main Results:

• MCs exhibit a distinct core-shell microstructure with Ti segregation in the core and Ta enrichment in the shell.
• A high density of chromium-rich stacking faults was observed within the Ti-rich cores.
• Chromium-rich M₂₃C₆ precipitates were found at the terminations of these stacking faults, suggesting a link to MC decomposition.

Conclusions:

• The core-shell structure of MCs influences their stability and decomposition pathways.
• Stacking faults and associated M₂₃C₆ precipitates are implicated in the decomposition of MCs.
• This research provides new insights into defect-carbide interactions, crucial for designing robust superalloys.