| Popis: |
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A new class of ductile metal reinforced bulk metallic glass matrix composite material has been prepared that demonstrates improved mechanical properties. This newly designed material exhibits both improved toughness and large plastic strain to failure. Primary dendrite growth accompanied by solute partitioning in the molten state yields an equilibrium microstructure consisting of a ductile crystalline Ti-Zr-Nb [beta] phase, with the bcc-structure, in a Zr-Ti-Nb-Cu-Ni-Be bulk metallic glass matrix processed via in situ processing. Under mechanical loading, the microstructure imposes constraints on the glassy matrix that leads to the generation of highly organized shear band patterns throughout the sample. This results in a dramatic increase in the plastic strain to failure, impact resistance, and toughness of the metallic glass. This thesis shows how microstructural inhomogeneity can be used to control the initiation and propagation of localized shear bands in metallic glasses under a variety of unconstrained loading conditions. A series of mechanical property tests were conducted on composite materials. These include quasi-static tensile and compression tests, Charpy impact, and three point bend tests on specimens prepared according to ASTM standards. Also, in situ straining transmission electron microscopy (TEM) experiments were performed to study the propagation of the shear bands in the bulk metallic glass based composite. |
