Wang, Tianyao (2020-08). Radiation Responses of Bulk Metallic Glasses: Fundamental and Application Studies. Doctoral Dissertation.
Amorphous metallic glasses (MGs) convert to crystalline solids upon annealing at a temperature greater than their glass transition temperature. Such a phase change, however, does not occur in the presence of local melting caused by damage cascades introduced by ion irradiation. Although the resulting thermal spikes can reach temperatures greater than 1000 K, the quenching rate of the local melting zone is several orders of magnitude higher than the critical cooling rate for MG formation. Thus, the amorphous structure is sustained. This mechanism increases the highest temperature at which irradiated MG sustains the amorphous phase. If MG is pre-annealed to form a polycrystalline structure, irradiation can locally convert this crystalline phase to an amorphous phase if the grains are nanometers in size and comparable to the damage cascade volume size. For larger grain sizes, the amorphization by ion irradiation does not occur. Combining pre-annealing and site-selective ion irradiation, patterned crystalline-amorphous heterogeneous structures have been fabricated, and demonstrate the capability to arrest cracks at amorphous-crystalline interfaces. This finding opens new doors for various applications from data storage to radiation detection.