Microstructure, mechanical properties and phase transformations of aluminum-based metallic glasses

The microstructure, nucleation and growth of a metastable crystalline precipitate, mechanical properties and microstructure/property relationships of the newly developed aluminum based metallic glass materials have been investigated in this study. These alloys reveal unusual mechanical properties, with several compositions having fracture tensile strength over 1000MPa, greatly exceeding that of high strength aluminum alloys. Their high strength and low density makes them potential engineering materials.;Rapidly solidified aluminum alloys were found to have true amorphous structures instead of microcrystalline or microquasicrystalline structures. The microstructure of partially crystallized metallic glasses is that of tiny crystalline precipitates (5-10nm) formed homogeneously embedded in an amorphous matrix. The properties of the material are greatly affected by the interaction between these tiny crystalline precipitates and slip bands.;For the first time, the deformation induced crystallization on the slipped planes (slip bands) was discovered in metallic glass materials. The microstructure of the Slip-Band/Crystalline Precipitate (SBCP) layer, which was produced by deformation, was determined. The formation mechanism of the plastic deformation induced crystallization was discussed.;Homogeneous nucleation and growth of precipitate in aluminum based metallic glasses were studied employing X-ray diffractometry, TEM and DSC. Several nucleation and growth theories were used in the study and various thermodynamics and kinetics parameters of Al;The failure of metallic glasses was analyzed and the fracture modes were examined. A new failure model of metallic glass was established based on experimental results. The fracture tensile strength and ductility were found to be very sensitive with the changing microstructure. This was explained by the amorphous matrix embrittlement due to thermal annealing and the interaction between the slip bands and the crystalline precipitates. Several models of interaction between crystalline precipitates and slip bands were discussed.