29th Magnetic Materials Center Seminar
November 13, 2006, 10:30
7th floor seminar room, Sengen
Nanocrystallization and plastic deformation in metallic glass
K. Mondal
The relation between nanocrystallization and plastic deformation of bulk metallic glass (BMG) is still not fully understood. There are some reports that show large plastic strain in uniaxial compression due to nanoscale crystallites forming along the shear bands or due to the hindrance from existing nanocrystals to the plastic flow along the single shear band, which helps in multiplication of shear bands. Recent studies in Cu-based and Ti based BMGs show that there is direct relation between nanocrystal formed during processing steps with plastic deformability of metallic glass. It is shown that there is some optimum level of nanocrystals which, in fact, imparts large plastic deformation. However, present emphatic results obtained from two newly engineered Zr-based BMGs, which indicate great enhancement of plastic deformability because of optimum level of nanocrystallization, strengthen the above concept.

Effect of micro alloying additions on the hardening response and precipitate microstructures of Mg-2.3at%Zn alloy
C. Mendis
Mg-Zn alloys such as ZK60 (Mg-2.3at%Zn-0.11at%Zr) are used in wrought alloy applications. Precipitation hardening following mechanical processing of an alloy could potentially increase the strength of an alloy significantly as evidenced by majority of the heat treatable Al alloys used everyday. However, these alloys are not precipitation hardened following extrusion or rolling operations due to very small age hardening response exhibited by Mg-Zn alloys. The low precipitation hardening response has been attributed to the low number density of precipitates found in Mg-Zn alloys at the peak hardening condition. Micro alloying additions is an effective method to increase the number density of precipitates and refine the precipitate sizes resulting in increase in hardening response without resorting to additional heat treatments. In this presentation, an attempt at increasing the peak hardness, through refinement of precipitates through addition of various micro alloying additions will be discussed.