Development of Strong-yet-Ductile Nanograined Alloys with Intergranular Amorphous Films Based on Metallic-Glass Templates

Description

It is well known that nanograined metals (NMs) have a great potential as the next generation structural materials because of their high strength due to grain size refinement induced strengthening, as manifested in the Hall-Petch law. However, the abundance of grain boundaries, which are simply planar defects, could be problematic and cause issues, such as poor thermal stability and low fracture toughness, for the application of the NMs. To mitigate these issues, there was a surge of interest recently to transform a regular grain boundary into an ultra-thin amorphous film. To achieve this, the prior efforts were mainly focused on alloying a proper element into an existing NM, which could subsequently segregate into grain boundaries and cause amorphization therein. While this approach was already demonstrated to be effective on a few binary/ternary alloys, however, it is difficult to be extended to the multicomponent alloy systems with functional applications, such as Fe-based soft magnetic alloys, or the multicomponent alloy systems with economic advantage, such as Al-based alloys, owing to the increased chemical complexity in these systems. In this project, we propose several strategies to develop nanograined multicomponent alloys with an intergranular amorphous phase. In sharp contrast to the prior approach, we will start with a multicomponent metallic glass system as a template to develop the desired nanograined alloys. Through a well-designed protocol entailing ultrasonic excitation and thermal treatment, we are able to tune the properties of the intergranular amorphous phase in a systematic way, such as its thickness, composition, strength and the plastic flow ability. Once the project was funded, we will achieve the following goals through the combined efforts from experiments, theoretical modeling and atomistic simulations, which include (1) to understand the thermodynamic/microstructural mechanism for the formation of a nanograined structure in a metallic glass, (2) to understand the micromechanical mechanism to overcome the strength-plasticity trade-off in the obtained nanograined alloy, and (3) to provide the protocol that could enable people to develop the nanograined multicomponent alloy with a controlled intergranular amorphous phase and therefore desired properties. The outcome of the proposed research is expected to strengthen the position of Hong Kong as a hub in the fundamental research in metals and alloys, which could benefit the local manufacturing industries within the Guangdong-Hong Kong- Macao Greater Bay Area in the long run.