||Over the past decades, bulk metallic glasses (BMGs) have attracted extensive interests|
because of their unique properties such as good corrosion resistance, large elastic limit, as
well as high strength and hardness. However, with the advent of micro-electro-mechanical
systems (MEMS) and other microscaled devices, the fundamental properties of
micrometer-sized BMGs have become increasingly more important. Thus, in this study, a
methodology for performing uniaxial compression tests on BMGs having micron-sized
dimensions is presented.
Micropillar with diameters of 3.8, 1 and 0.7 μm are fabricated successfully from the
Mg65Cu25Gd10 and Zr63.8Ni16.2Cu15Al5 BMGs using focus ion beam, and then tested in
microcompression at room temperature and strain rates from 1 x 10-4 to 1 x 10-2 s-1.
Microcompression tests on the Mg- and Zr-based BMG pillar samples have shown an
obvious sample size effect, with the yield strength increasing with decreasing sample
diameter. The strength increase can be rationalized by the Weibull statistics for brittle
materials, and the Weibull moduli of the Mg- and Zr-based BMGs are estimated to be about
35 and 60, respectively. The higher Weibull modulus of the Zr-based BMG is consistent with
the more ductile nature of this system.
In additions, high temperature microcompression tests are performed to investigate the
deformation behavior of micron-sized Au49Ag5.5Pd2.3Cu26.9Si16.3 BMG pillar samples from
room to their glass transition temperature (~400 K). For the 1 μm Au-based BMG pillars, a
transition from inhomogeneous flow to homogeneous flow is clearly observed at or near the
glass transition temperature. Specifically, the flow transition temperature is about 393 K atthe strain rate of 1 x 10-2 s-1.
For the 3.8 μm Au-based BMG pillars, in order to investigate the homogeneous
deformation behavior, microcompression tests are performed at 395.9-401.2 K. The strength
is observed to decrease with increasing temperature and decreasing strain rate. Plastic flow
behavior can be described by a shear transition zone model. The activation energy and the
size of the basic flow unit are deduced and compared favorably with the theory.