Study Of Mechanical Behaviors and Structures of Bulk Metallic Glasses with High-energy Synchrotron X-Ray Diffraction

Author

Feng JiangFollow

Date of Award

8-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Peter K. Liaw

Committee Members

Hahn Choo, Takeshi Egami, John D. Landes

Abstract

This dissertation addresses two critical issues in the mechanical behaviors and structures of bulk-metallic glasses (BMGs): (1) the effect of composition, fabrication method, and pretreatment of plastic deformation on mechanical properties and structures of BMGs; (2) the mechanical response and structural evolution of BMGs in the elastic and plastic region.

(Cu₅₀Zr₅₀)₉₄Al₆ and (Cu₅₀Zr₅₀)₉₂Al₈ amorphous alloys were used to study the effect of composition on mechanical properties and structures of BMGs. The (Cu₅₀Zr₅₀)₉₄Al₆ alloy exhibits lower yield stress and Young’s modulus, higher Poisson’s ratio, worse thermal stability, and better plasticity than (Cu₅₀Zr₅₀)₉₂Al₈. Both the topological and chemical effects of Al addition account for the differences of mechanical and physical properties between them.

A Zr₅₅Ni₅Al₁₀Cu₃₀ glass-forming alloy with injection casting (the melting temperatures are 1,550 K and 1,250 K, respectively) and with suction casting was fabricated. The results indicate that despite their amorphous structures, the suction-casting samples exhibit a lower yield stress, lower Young’s modulus, and larger plastic strain than the injection-casting samples (the melting temperature is 1,550 K) due to more quenched-in free volumes in suction casting, which results from the higher cooling rate.

The inhomogeneous plastic deformation in Zr₅₀Cu₄₀Al₁₀ BMG samples was introduced by four-point-bend fatigue. There is almost no difference of the stress-strain behaviors between the deformed and undeformed samples. Elastostatic compression was used to introduce homogeneous deformation in Zr₇₀Cu₆Ni₁₆Al₈ BMG samples. The preloaded samples are softer with decreases of yield strength and Young’s moduli. Anisotropy was observed in the preloaded samples despite their small magnitudes, which even occurred at a relatively low temperature and applied stress level.

The structural evolution of Zr₇₀Cu₆Ni₁₆Al₈ BMG in the elastic region was analyzed with anisotropic pair density function. The analysis of the first shell of Zr₇₀Cu₆Ni₁₆Al₈ glass confirms the structural changes in the elastic region. The bond reorientation leads to direction dependent changes in the chemical short-range order. The structural evolution in the plastic region of Zr₇₀Cu₆Ni₁₆Al₈ BMG is investigated as well. The serrations were observed for both the stress-displacement and full width at half maximum-displacement curves. The excess free volume was measured, which increases with increasing the displacement.

Recommended Citation

Jiang, Feng, "Study Of Mechanical Behaviors and Structures of Bulk Metallic Glasses with High-energy Synchrotron X-Ray Diffraction. " PhD diss., University of Tennessee, 2011.
https://trace.tennessee.edu/utk_graddiss/1049