Studying the Fatigue Behavior of Zr-Based Bulk-Metallic Glasses and Composites

Author

Gongyao Wang, University of Tennessee - Knoxville

Date of Award

12-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Peter K. Liaw

Committee Members

Chain T. Liu, John D. Landes, Hahn Choo

Abstract

As excellent candidates for structural materials, the mechanical behavior of bulk metallic glasses (BMGs) is being widely studied. Although their fatigue behavior is very important for engineering applications, there are few studies on their fatigue behavior. Moreover, the understanding of the fatigue behavior is pretty limited.

High-cycle fatigue experiments were conducted on notched Zr-based BMGs under tension-tension loading in air and vacuum at room temperature. A sparking phenomenon was found by infrared camera at the final fracture moment of Zr₅₀Al₁₀Cu₃₀Ni₁₀ in air. The fatigue-endurance limit (983 MPa) of Zr₅₀Cu₃₇Al₁₀Pd₃ was greatest among these Zr-base BMGs in air. The fatigue lives in vacuum and air are generally similar.

LM001 and LM002 are commercial Zr-based BMGs. The X-ray diffraction results show that LM001 is a monolithic BMG and LM002 is a BMG composite containing crystalline phases. The fatigue-endurance limit (239 MPa) of LM002 was found to be significantly lower than that (567 MPa) of LM001, which indicates that the crystalline phase could degrade the resistances to fatigue.

The compression strengths of Zr-based BMGs with partial crystallization are comparable to those of their fully amorphous alloys. However, the fatigue-endurance limits of these BMGs with partial crystallization were much lower than those of their fully amorphous alloys, which suggested that the fatigue behavior of a BMG is very sensitive to the microstructure.

Fatigue cracks initiate from the outer surface of the sample, inclusions, and/or porosity. The propagation region exhibits a typical striation-type fracture. The final fast fracture region was very rough and occupied most of the fracture surface. The vein pattern and droplets with a melted indication were observed in the apparent melting region. A mechanistic understanding of the fatigue behavior of the Zr-based BMGs is suggested.

The ratio of the fatigue-endurance limit to the tensile strength seems to increase with increasing Poisson’s ratio. Moreover, The fatigue endurance limits of Zr-based, Cu-based, and Fe-based BMGs and composites were comparable to those of ductile crystalline alloys. The fatigue-endurance ratios of Zr-based BMGs were found to be comparable with those of high strength crystalline alloys.

Recommended Citation

Wang, Gongyao, "Studying the Fatigue Behavior of Zr-Based Bulk-Metallic Glasses and Composites. " PhD diss., University of Tennessee, 2006.
https://trace.tennessee.edu/utk_graddiss/2061