Ultrasonic Investigation of the Elastic Properties and Liquid Fragility of Bulk Metallic Glasses in the Supercooled Liquid Region

Citation

Lind, Mary Laura (2008) Ultrasonic Investigation of the Elastic Properties and Liquid Fragility of Bulk Metallic Glasses in the Supercooled Liquid Region. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3B4B-ZV48. https://resolver.caltech.edu/CaltechETD:etd-10262007-104725

Abstract

In this thesis new methods for accessing the ultrasonic properties of supercooled liquid region in bulk metallic glass forming liquids were developed. An extensive examination of the relationship between the elastic properties of metallic glasses and liquid fragility has been undertaken. Three experimental techniques were created/modified to access the Supercooled Liquid Region of the glass: annealing relaxation measurements, delay line measurements, and long notched-rod measurements. The methods as well as the limitations are discussed.

Ultrasonic contact methods with measurement frequencies of 25MHz have been used for in situ and ex situ examination of the elastic properties of the supercooled liquid region (SCLR) in bulk metallic glasses (BMGs). Ex situ relaxation experiments in Vitreloy-4 (Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5) were performed that demonstrated that in the glassy state, the low-temperature dependence (from 78K to 298K) of the elastic modulii is linear as expected from Debye-Gruneisen theory. In the liquid state, the temperature dependence of the shear modulus was found to be stronger than that of the bulk modulus. The strong temperature dependence of G is found to be an important aspect of the recently developed Cooperative Shear Model. Additionally, this temperature dependence of the shear modulus in the liquid state was found to directly relate to the viscosity (or fragility) of the liquid. In situ experiments, utilizing delay lines and notched-rods, were performed on BMGs with a range of fragilities. Improvements to the model relating viscosity, shear modulus, and liquid fragility are presented. The results from both types of measurement (in and ex situ) compared favorably; thus supporting the claim that we are measuring the properties of the equilibrium supercooled liquid. Additionally, these results are used support the idea that the shear modulus relates to a unique potential energetic state of the glass.

Thesis Files