Investigation of Mechanical Properties of Frontier Materials, Including Thermoelectric Materials and Metallic Glass
Date Issued
2015
Date
2015
Author(s)
Liu, Cheng-Yun
Abstract
Metallic glasses have unique properties that can be served as a diffusion barrier and can be put in thermoelectric devices. The investigation of the basic mechanical properties of both materials is implemented in this thesis for the promising combination of these two materials in the future. In the first part of this thesis, the room temperature mechanical properties of N-type ZrNiSn and P-type tetrahedrite systems were investigated. To study the mechanical properties of ZrNiSn, different powder processing methods and sintering temperatures were applied to introduce different porosities and microstructures. The elastic moduli were measured by analyzing the resonant ultrasonic spectra, and they were found to decrease exponentially as the porosity increased. Excess Ni has been characterized to cause the elevation of theoretical density of the material. The high energy ball milled specimens had higher Young’s modulus with the antisite defect introduced by this processing method. The room temperature mechanical properties of tetrahedrite system were also investigated, including natural mineral and 50-50 natural synthetic tetrahedrite. Slow crack growth behavior was monitored in this study. There was no obvious crack growth even in the high humidity environment. Experiments of adding SiC nanoparticles and graphene nanoplatelet into the tetrahedrite as promising strategies to enhance the fracture toughness were performed. However, no distinct improvement was found in this study. In the second part of this thesis, the unique deformation method, scissors cutting was applied to Fe-based metallic glass ribbon, and the corresponding shear band behavior was characterized with the aid of finite element simulations. Metallic glass alloys exhibit impressive mechanical properties including large elastic strain to failure and high tensile strength resulting from their amorphous nature that have attracted people’s attention to this new generation of material. However, their plasticity is dominated by the shear band behavior and always appears to be nearly brittle. A regular shear band patter was observed after the scissors cutting reached a steady-state. The result indicates that the shear band shows its stability under specific stress state. Furthermore, the result provides a simple and attainable way to control shear banding. The finite element analysis was performed to simulate the stress field resulting from cutting the metallic glass ribbon. The result verified that the shear band formation is controlled by the shear stress.
Subjects
thermoelectric materials
porosity
mechanical properties
metallic glass
shear band
scissors cutting
finite element simulation
Type
thesis
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