Structure and Mechanical Properties Control of Bulk Metallic Glasses by Electropulsing Treatment
DescriptionMany bulk metallic glasses (BMGs) are known to have attractive material characteristics such as high levels of strength-to-weight ratio and reasonable toughness, and yet being flexible. Indeed this has led to their use in a wide variety of high performance applications ranging the golf club to micromachine components. The study on their mechanical properties is currently a critical topic in BMG research. In particular, shear band formation is thought to be a universal mechanism of the deformation of metallic glasses. The formation of shear bands in BMG during deformation is actually a complex kinetic process. Because of the incomplete knowledge of BMGs structures on an atomic-level, the exact nature of local atomic motion taking place during shear transformation is not fully resolved. In the present investigation, the PI and co-workers propose to study the mechanical responses of Y54Al23Ni23, (Zr65Al10Ni10Cu15)95Nb5and Ni60Nb15Zr20Al5BMGs caused by electric pulse induced structure relaxation or transformation. The three types of BMGs are chosen to represent BMGs ranging from extremely brittle to reasonably tough. Electropulsing treatment is a relatively recent process for inducing microstructure changes or improving workability of alloys by passing current pulses of current densities larger than 1000 A/cm2. Structure relaxation, crystallization, phase transformation, etc. can take place in alloys within a few seconds of electropulsing treatment compared with hours taken for conventional thermal annealing. Under uniaxial compression, the thickness and the shape of shear bands as a function of strain rate and BMG structures will be studied using low aspect (height/diameter) ratio specimens. The structure evolutions within the shear bands will be studied using high-resolution transmission electron microscopy. The project ultimately aims to produce important evidence that will lead to a more comprehensive rationalization of the shear banding mechanism, thus enabling a practical strategy to engineer the properties of the BMGs to suit applications that are more demanding.
|Effective start/end date
|1/10/08 → 7/06/12