Effect of Ta on glass formation, thermal stability and mechanical properties of a Zr52.25Cu28.5Ni4.75Al9.5Ta5 bulk metallic glass

The effect of Ta on glass-forming ability, crystallization behavior and mechanical properties of Zr52.25Cu28.5Ni4.75Al9.5Ta5 bulk metallic glass (BMG) is investigated. The solubility of Ta in the Zr-base BMG alloy depends on the arc melting conditions. 3.2 at.% Ta dissolve in the alloy inducing an increase of about 20 K in both glass transition temperature and crystallization temperature of the BMG. However, Ta does not significantly change the extension of the supercooled liquid region. The remaining Ta particles in the master alloy may induce a composition-segregation layer around the particles upon subsequent casting. This further induces the crystallization of Zr2CU that deteriorates the ductility of the samples. The compressive strength and ductility of the as-cast 3 mm diameter Zr52.25Cu28.5Ni4.75Al9.5Ta5 samples are improved in comparison with the Zr55Cu30Ni5Al10 BMG alloy. The fracture plane of the present alloy has an angle of 31-33degrees with respect to the stress axis, which remarkably deviates from the maximum shear stress plane. The improvement of the mechanical properties and the peculiar fracture feature for the Zr52.25Cu28.5Ni4.75Al9.5Ta5 BMG alloy can be attributed to the effect of dispersed Ta particles. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.