Chemistry (intrinsic) and inclusion (extrinsic) effects on the toughness and Weibull modulus of Fe-based bulk metallic glasses

Abstract

Systematic changes in composition were employed to increase the notch toughness of a variety of Fe-based Bulk Metallic Glasses (BMGs). The Fe₅₀Mn₁₀Mo₁₄Cr₄C₁₆B₆ BMG possessed very high hardness (e.g. 12 GPa) but very low notch toughness (e.g. 5.7 MPa m^1/2) at room temperature, consistent with fracture surface observations of brittle features. Many of the other Fe-BMG variants, created to change the Poisson's ratio via systematic changes in alloy chemistry, exhibited higher toughness but more scatter in the data, reflected in a lower Weibull modulus. SEM examination revealed fracture initiation always occurred at inclusions in samples exhibiting lower toughness and/or Weibull modulus for a given chemistry. Implications of these observations on reliability of BMGs are discussed.

Keywords:

• Fe-based metallic glasses
• mechanical properties
• toughness
• Weibull modulus

Acknowledgements

The research is supported by the DARPA Structural Amorphous Metals Program under ONR Grant No. N00014-06-1-0492. Dr D.Q. Li is thanked for the SEM micrographs. The assistance of Prof. D. Schuele with elastic constants measurements at CWRU is gratefully acknowledged. The document is approved for public release, distribution unlimited.