Stretching the Limits in Thermoplastic Forming of Bulk Metallic Glasses

Rodrigo Miguel Ojeda Mota, Yale University Graduate School of Arts and Sciences


Metallic glasses (MG) suggest that superb mechanical properties can be paired with plastic-like processing. Their high strength and elasticity are often paired with fracture toughness. Their supercooled liquid region gives rise to plastic-like processing and suggests parts and shapes that can otherwise not be obtained for crystalline metals. However, current processing techniques only allow for limited options in terms of geometry, thicknesses uniformity, and shape complexity. In the first part of my thesis, I introduce the form-giving aspect of metallic glass thermoforming, by introducing stretch blow molding, to expand the geometries that can be fabricated with metallic glasses. For this I developed a model, which allows to quantify stretch blow molding and provides insight into its potential use and limitations. We demonstrate that with stretch blow molding overall strains exceeding 2000% are achievable, significantly higher than the previously reported ~150% of blow molding. In the second part of my thesis, I focused on the effect of the processing on metallic glasses properties. This is motivated by the current understanding that most metallic glasses lack sufficient ductility or toughness when fabricated under conditions resulting in bulk glass formation. To address this shortcoming, I used strain rate to excite the liquid while simultaneously cooling it to freeze the excited liquid into a glass with a higher fictive temperature. Microscopically, straining causes the structure to dilate, hence “pulls” the structure energetically up the potential energy landscape. Upon further cooling, the resulting excited liquid freezes into an excited glass that exhibits enhanced ductility. I used Zr44Ti11Cu10Ni10Be25 as an example to pull metallic glasses through this excited liquid cooling method, which can lead to the tripling of bending ductility.