Source: Dissertation Abstracts International, Volume: 78-11(E), Section: B.

Adviser: Andre D. Taylor.

Metallic glasses (MGs) are of particular interest for various applications such as electrocatalyst, biomedical devices and etc, because oftheir merits in vast material choices, versatile formability down to nanostructures, and maintaining a homogeneous and isotropic material at atomic level without any grain boundaries or dislocations. These unique properties allow MGs exhibit physically high strength and elasticity, and electrochemically good corrosion resistance as well as potential as electrocatalysts with high activity and durability.

Bulk metallic glasses (BMGs) were shown previously to be highly active and durable electrocatalysts, as well as promising biocompatible materials. However, the limited number of good glass formers that can form BMGs hinders the development of MGs in multiple areas. Therefore, we adopt three approaches in this work to increase the competency of MGs for broader applications: 1) Bypass the limited good glass formers for BMGs by applying a combinatorial study on thin film metallic glasses (TFMGs), so as to screen the compositions that exhibit promising performance; 2) Apply both additive and subtractive modification techniques to BMGs to improve the electrocatalytic activity; 3) Use a bottom-up approach instead of the traditional top-down approach that is heavily dependent on the glass forming ability of BMGs, to synthesize metallic glass nanostructures (MGNs) as electrocatalysts.

Mg-Ca-Zn BMGs exhibit promising mechanical properties and biocompatibility. Here we synthesized thin film metallic glasses and study the corrosion characteristics on a wide composition range, Mg(35.9-63)Ca(4.1-2I)Zn(17.9-58.3), exemplified using twelve distinct compositions. The results show that the new Mg--Zn--Ca metallic glasses provide significantly more noble corrosion potentials and enhanced corrosion resistance relative to pure Mg. We find between 4 to 21 at.%, a higher initial Ca content will lead to a higher Ca loss after the polarization by plotting the delta Ca content versus initial Ca content. In addition we discover a clear relationship between Zn content and corrosion current that Mg-Ca-Zn metallic glasses with Zn content between 50 to 60 at.% should exhibit the minimum corrosion current, whereas higher and lower Zn content all increase the dissolution rate. These results showcase the benefit of evaluating a larger alloy compositional space to discover superior biocompatible materials.

We also examine the oxygen reduction reaction performance of a combinatorial Pd-AuAg-Ti thin film library using high-throughput screening and correlate the electrochemical behavior to the crystallographic properties. We find compositions of ca. 40-60 at.% Pd and 30-35 at.% Au are shown to exhibit both low overpotential of close to the value of pure Pt as well as high current density. We also observe a volcano-like relationship between the overpotential and the solid formation strain. This study provides compositional guidance towards the future synthesis ofnanostructured quaternary Pd-Au-Ag-Ti alloys and suggests.