Date: Thursday, Jan 21st
Presenter: Bosong Li, OSU Materials Science
Bulk metallic glasses (BMGs) as one kind of relatively new amorphous materials have received much attention in recent years. Rapid cooling method from liquid state provides the possibility to bypass crystallization during solidification process. Due to the lack of crystal defects such as grain boundaries and dislocations, BMGs can have some special properties such as high yield strength and high elastic strain limit. And as an important mechanical property, fracture toughness can also provide much information for engineering design, and understanding the fracture behavior of BMGs becomes necessary for mechanical applications and material specification. In recent year studies, it shows that the fracture toughness of different BMGs varies significantly from brittle to quite high damage tolerance. However, BMGs have been reported to have large variability in mode I fracture toughness even in one type. The primary aim of this thesis project is to understand the effect of one thermomechanical method on the fracture behavior of BMGs. In this study, alternating soft and hard regions were created in a Zr52.5Ti5Cu18Ni14.5Al10 (at.%) BMG via mechanical imprinting at room temperature. The results showed that only 50% of as-cast samples demonstrated plastic deformation during mode I fracture tests, 100% of imprinted samples demonstrated measurable plasticity and the scatter in measured mode I fracture toughness was significantly reduced. Mechanical treatments show promise for improving fracture reliability of BMGs.