This project is dedicated to a novel class of metallic materials that are called metallic glasses (MGs). Opposite to normal metallic alloys, MGs have a disordered atomic structure, which makes them more like a frozen liquid than a crystal. This change in structure brings a long a series of advantages over conventional engineering metals, such as steels. However, one problem with MGs is that their processing is very difficult. The sensitivity of the glassy structure to various processing parameters leads to a large variety of structures and therefore properties. This limits the widespread use of MGs in applications and thus the exploitation of their exceptional properties. In order to overcome this problem, the PI uses a novel route of elastic loading protocols that aim at introducing a defined and quantifiable structural state, irrespective of casting history. The goal is to achieve a structural reference state that subsequently can be relaxed via thermal processing to any desired state and its corresponding property. If successful, this project therefore provides a reversible thermo-mechanical processing method that puts an end to the ill-defined structural states and property variations originating from MG casting. Such an advance will significantly promote the usage of these novel alloys in engineering applications, enabling, for example, more energy efficient devices, novel consumer goods, high-performant medical devices, or magnetic components.
Defined thermo-mechanical protocols are a key to target specific microstructures and therefore properties. Such knowledge is used in daily industrial operations to obtain a desired mechanical performance of crystalline metallic materials. Modifying the structure, and therefore mechanical properties of disordered metallic materials, also known as metallic glasses (MGs), is much less straightforward due to the lack of well-defined structure-property relationships. Furthermore, the lack of apparent length scales in the amorphous MG makes it very difficult to identify a given structural state. Therefore, one normally uses the measure of stored excess enthalpy to characterize the structural state. In this research project, the PI addresses this shortcoming by i) homogeneous rejuvenation via stresses within the elastic regime, and ii) by demonstrating how spatial correlation lengths of property fluctuations at different length scales directly quantify a given excess enthalpy state. This is achieved by using site-specific characterization methods at the micron- and nanoscale. The experiments will reveal saturation limits of rejuvenation, from which the PI constructs a thermo-mechanical deformation map on how to prepare well-defined and quantifiable structural states. If successful, this research project introduces a novel structure-property relationship for tailoring properties of MGs.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
