The Cu47Ti34Zr11Ni8 glass-forming alloy : thermophysical properties, crystallization, and the effect of small alloying additions on the thermal stability

Author: Glade, Stephen Clarke

Year: 2001

Degree: Dissertation (Ph.D.)

Advisor: Johnson, William Lewis

Committee Members: Johnson, William Lewis; Atwater, Harry Albert; Bhattacharya, Kaushik; Haile, Sossina M.

Option: Materials Science

DOI: 10.7907/4ZJQ-RP66

Abstract

The thermophysical properties, crystallization, and the effect of small alloying additions on the thermal stability of Cu47Ti34Zr11Ni8 were investigated. The thermophysical properties studied were specific heat capacity and viscosity. From the specific heat capacity data, the differences in the thermodynamic functions between the liquid and the crystalline states of Cu47Ti34Zr11Ni8 were calculated. A lower Gibbs free energy difference between the liquid and the crystalline states generally indicates a better glass-forming ability of an alloy. A lower entropy of fusion indicates a better glass-forming ability as well. The viscosity data, using the strong/fragile classification of glasses, also give a measure of the glass-forming ability of the alloy.

The crystallization of amorphous Cu47Ti34Zr11Ni8 was studied with many experimental techniques. Similar to other metallic glass-forming alloys, Cu47Ti34Zr11Ni8 phase separates prior to crystallization. Cu47Ti34Zr11Ni8 decomposes to copper-enriched and titanium-enriched regions (the copper-enriched regions are low in titanium and vice versa). Primary crystallization of Cu47Ti34Zr11Ni8 consists of face centered cubic nanocrystals growing in an amorphous matrix.

The glass-forming ability of certain metallic glass-forming alloys has been improved with small silicon additions, which has been attributed to silicon destabilizing oxide nucleation sites. To investigate this further, a study of the effect of silicon on the crystallization of Cu47Ti34Zr11Ni8 was performed. Prior to crystallization, both Cu47Ti34Zr11Ni8 and Cu47Ti33Zr11Ni8Si1 phase separate to copper-enriched and titanium-enriched regions. A face centered cubic phase then nucleates and grows in both alloys. No change in the local composition around a silicon atom in Cu47Ti33Zr11Ni8Si1 was detected.

Small additions of magnesium and germanium were added to Cu47Ti34Zr11Ni8 to observe the effect on the thermal stability of the alloy. In contrast to the results observed with silicon, no improvement in the glass-forming ability was observed. However, there was an improvement in the thermal stability of the alloy against crystallization in the supercooled liquid regime with both the magnesium and germanium additions.

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