Elastic Properties of Bulk-metallic Glasses Studied by Resonant Ultrasound Spectroscopy

Author

Zhiying Zhang, University of Tennessee - Knoxville

Date of Award

8-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Veerle Keppens

Committee Members

Takeshi Egami, Peter K. Liaw, James R. Thompson

Abstract

The elastic properties of a solid are of considerable interest to both science and technology. Not only do they contain fundamental information about the nature of the inter-atomic bonding in the material, but they also determine the mechanical behavior of solids. In the past few years, considerable effort has been devoted to the study of elastic properties of bulk metallic glasses (BMGs), a relatively new class of metallic materials that display a unique combination of mechanical and physical properties. Our research has focused on Zr-based, Cu-based and Ca-based metallic glasses. Zr-based BMGs are known to have superior glass forming ability and high strength, but their ductility is too low for wide-spread practical applications. Cu-based BMGs recently received wide interest because of their low cost and good mechanical properties. Ca-based BMGs have low glass transition temperature T_g, around 390 K, which make them very attractive to be studied near T_g.

In this work, resonant ultrasound spectroscopy (RUS) has been applied to study the elastic properties of above mentioned BMGs from 5 K to their glass transition temperature T_g. RUS is a novel technique for determining the elastic moduli of solids, based on the measurement of the resonances of a freely vibrating body. In an RUS experiment, the mechanical resonances of a freely vibrating solid of known shape are measured, and an iteration procedure is used to “match” the measured lines with the calculated spectrum. This allows determination of all elastic constant of the solid from a single frequency scan.

Below T_g, the elastic constants of the BMGs under investigation show “normal” behavior, i.e. with increasing temperature, all moduli decrease and Poisson ratio increases. Above T_g changes in the trends occur due to structural relaxation and crystallization. We confirmed the suggested link between ductility and Poisson ratio: BMGs showing good ductility display high Poisson ratio. By increasing palladium content in Zr₅₀Cu_40-xAl₁₀Pd_x alloys, BMGs with high Poisson ratio and thus good ductility have been obtained. In addition, we developed a simple model to provide fast and good estimate of the temperature dependence of elastic constants of BMGs from room temperature measurements.

Keywords: Elastic properties; Bulk metallic glasses (BMGs); Resonant ultrasound spectroscopy (RUS); Internal friction.

Recommended Citation

Zhang, Zhiying, "Elastic Properties of Bulk-metallic Glasses Studied by Resonant Ultrasound Spectroscopy. " PhD diss., University of Tennessee, 2008.
https://trace.tennessee.edu/utk_graddiss/430