Effect of Nb on Transformation Kinetics and Mechanical Properties in Zr-Al-Ni-Cu Metallic Glasses

Abstract

The effect of Nb addition on the nucleation and grain growth behaviors has been investigated in the monolithic Zr65Al7.5Ni 10Cu17.5Nb5 metallic glass. Nb has been well-known as an element for icosahedral quasicrystalline (QC) phase formation in the primary crystallization stage as well as for improving mechanical properties and corrosion resistance. The grain growth rate of the QC phase at near the crystallization temperature is 1.2×l0-9 m/s, which is approximately 10 times smaller than that of the primary fcc Zr2Ni phase in the Zr65Al7.5Ni10Cu17.5 metallic glass. In contrast, nucleation rate increases drastically by Nb addition. It can be calculated as 1.2×1021/m3 s, which is approximately 105 times larger than that of the Zr 65Al7.5Ni10Cu17.5 alloy. The results indicate that Nb is a very effective element for controlling grain growth and nucleation rates. Good plasticity is exhibited in the as-cast alloy, however, it is lost drastically even after the structural relaxation as well as the QC precipitation. Such significant change may be attributed to the local ordering and/or phase separating tendencies by a positive chemical affinity of the Zr-Nb pair. © 2010 The Japan Institute of Metals.