Improving Fracture Fatigue Resistance in Metallic Glass through Controlled Structural Evolution and Sample Architecture Design

Description

Metallic glasses are well known for their superb strength and high elastic limit;however, their fatigue resistance, in terms of fatigue endurance limit, is usually low,being less than 10% of their ultimate tensile strength according to the prior results.Aside from the lack of tensile ductility, this also hinders the use of metallic glasses as astructural material. Meanwhile, although the fracture toughness of some metallicglasses, such as Zr-, Pt- and Pd-based, is comparable to conventional alloys, thefracture toughness of some others that have important functional applications, such asFe-, Mg-, and Ca-based metallic glasses, are very limited. In order to mitigate theseproblems, metallic glasses are often being mixed with crystalline phases to formmetallic-glass matrix composites. Despite that the composite approach was effective onsome alloy compositions, however, it also destroys the overall structural amorphousnessand simultaneously reduces the alloy strength, which is not desirable in the applicationswhich prefer a full amorphous structure. By comparison, we have recently shown that, bycarefully controlling the degree of structural rejuvenation in as-cast amorphous statesthrough thermo-mechanical treatments, appreciable tensile ductility of 2-4% can beachieved even in monolithic Zr-based bulk metallic glasses without scarifying theirtensile strength. In this project, we would like to propose further research, combiningexperimental, theoretical and computational efforts, to understand the underlyingphysical mechanisms behind this phenomenon of ductility enhancement and carry out asystematic study of the various methods, including the thermo-mechanical treatmentand sample architecture design, which can enhance not only tensile ductility but alsofracture and fatigue resistance in the metallic glasses with a high economic feasibilityfor industrial applications, such as Fe- and Mg-based. The successful implementation ofthe proposal is expected to achieve the following: (1) to construct a structural evolutionmap, as related to various thermo-mechanical treatments, which enables quantitativelycontrolling the degree of rejuvenation and/or relaxation of the amorphous structure in ametallic glass, (2) to understand and model the basic micromechanical processes offracture and fatigue damage in a metallic glass and (3) to provide guidelines forimproving fracture and fatigue resistance in metallic glasses through controlledstructural evolution and sample architecture design.