Critical Poisson ratio for room-temperature embrittlement of amorphous Mg₈₅Cu₅Y₁₀

Abstract

When prepared as a thin foil by rapid solidification, the Mg₈₅Cu₅Y₁₀ amorphous alloy undergoes a ‘ductile’/brittle transition upon bending after ageing at room temperature. This macroscopic behaviour arises from structural relaxation, which lowers the enthalpic content of the system and increases the elastic constants (i.e. the Young modulus and the shear modulus) as a function of ageing time. Since the shear modulus is found to increase faster than the Young modulus, the Poisson ratio decreases as the alloy ages and, at a critical value of ν ∼ 0.32, the ‘ductile’/brittle transition occurs. The results are discussed in terms of the annihilation of different types of defect, which characterize the disordered structure of a metallic glass.

Acknowledgments

The authors thank Bart Bollen and Theo Bollen for their help with measurements of the elastic moduli at the IMCE (Integrated Material Control Engineering) NV, Diepenbeek, Belgium. This work was financed by ETH Research Grant TH-21/04-2.

Notes

§Current address: NIS Centre of Excellence, Dipartimento di Chimica IFM, Università di Torino, via P. Giuria 7, I-10125 Torino, Italy.

Additional information

Notes on contributors

A. Castellero§

§Current address: NIS Centre of Excellence, Dipartimento di Chimica IFM, Università di Torino, via P. Giuria 7, I-10125 Torino, Italy.