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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
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Critical Crystallization for Embrittlement in Metallic Glasses
Jittisa Ketkaew1, Ze Liu1,2, Wen Chen1
1Department of Mechanical Engineering & Materials Science, Yale University, New Haven, Connecticut 06511, USA.
Physical Review Letters
|January 15, 2016
Summary
Crystallization above 6% dramatically reduces metallic glass toughness. A critical threshold exists for embrittlement, crucial for designing robust metallic glass materials.
Area of Science:
- Materials Science
- Solid State Physics
Background:
- Bulk metallic glasses (BMGs) offer unique properties but can be susceptible to embrittlement.
- Crystallization is a common phenomenon during BMG processing and can significantly alter mechanical properties.
Purpose of the Study:
- To investigate the effect of controlled crystallization on the fracture toughness of specific bulk metallic glasses.
- To identify a critical crystallization threshold leading to embrittlement in metallic glasses.
Main Methods:
- Fracture toughness measurements were performed on Zr-Ti-Cu-Ni-Be and Pd-Cu-Ni-P metallic glasses.
- Controlled crystallization was induced by annealing at various times to achieve different volume fractions of crystalline phases.
Main Results:
- Fracture toughness remained unaffected up to approximately 6% crystallization by volume.
- A sharp decrease in fracture toughness was observed beyond the 6% threshold, with a 50% reduction for each additional 1% of crystallization.
- The observed embrittlement transition at ~7% crystallinity is attributed to the interaction of crystal stress fields within the amorphous matrix.
Conclusions:
- A critical crystallization volume fraction exists, above which bulk metallic glasses undergo significant embrittlement.
- Understanding this critical threshold is vital for designing tougher metallic glass composites and optimizing processing protocols to prevent embrittlement during thermoplastic forming.
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