Designing in situ and ex situ bulk metallic glass composites via spark plasma sintering in the super cooled liquid state

• Coupling a fast heating rate with dynamic pressing is shown to enhance density of an iron-based BMG by 20%.
• This strategy can be used to achieve full density of marginal glass formers without having to increase the applied stress during processing.
• The strategy presented decouples the densification and devitrification processes so that they can be independently controlled.
• Independent control of densification and devitrification enables systematic design of dense composites with controlled microstructure.

Crystallization inhibits metallic glass forming in the super cooled liquid state and can be avoided if sufficiently fast heating rates can be obtained, but becomes increasingly difficult for marginal glass formers. We propose that dynamic pressing can enhance formability, and demonstrate that density of an iron-based marginal glass forming alloy (Fe49.7Cr17.1Mn1.9Mo7.4W1.6B15.2C3.8Si2.4) can be enhanced by coupling loading rate to fast heating rate during spark plasma sintering. We also describe the transformation kinetics for devitrification in a time–temperature–crystallinity diagram. The combination of coupled loading/fast heating and the time–temperature–crystallinity diagram define the processing requirements for obtaining a dense X-ray amorphous structure and can also be used to design a wide variety of dense in situ composites. Finally, we demonstrate that the design approach also applies to ex situ composites by adding microcrystalline W or Ta, enabling systematic control of atomic-, nano-, and micro-structure. This multi-scale structure control of bulk metallic glass composites has implications for developing a fundamental understanding of structure–property relationships. We expect this general approach will be applicable to other bulk metallic glass composites, and especially beneficial for marginal glass formers that are otherwise difficult to process.

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