Microscale Testing and Characterization Techniques for Benchmarking Crystal. . .
109
that each imparts. The FIB has been demonstrated to be quite useful for machining
sensitive materials or machining at length scales of tens of microns or less with high
precision and very low damage. The femtosecond laser, though still a relatively
new machining tool, has already been applied in enough cases to demonstrate its
utility in machining samples with a thickness ranging from tens of microns to a
few hundred microns, with damage scaling with laser beam energy, but able to be
controlled to less than a micron in most cases. Although wire EDM is a technique
typically applied at the macro scale, with proper optimization it can also be applied
at a scale on the order of a few hundred micrometers up to much larger scales, with
damage on the order of single-digit microns.
Understanding the capabilities of these three techniques allows a methodology
that facilitates machining of materials at multiple length scales in order to study size
effects. It can also be applied to develop sample geometries not only for microtensile
testing but for developing other microscale samples, such as microcantilevers for
studying fatigue or microbending samples for studying fracture toughness. The true
benefit of being able to apply these complimentary techniques lies in combining the
various techniques to improve the throughput of test samples in a way that has not
been achieved previously.
Developing techniques with different material-removal rates and applicable
length scales, and optimizing these techniques, is critical to the manufacture
and testing of microtensile samples. Sample quality has a significant impact on
microtensile results, especially at smaller length scales. There is an inherent
stochasticity that arises from testing materials at smaller length scales, specifically
in the single crystal and mesoscale regimes where microstructural features give rise
to a multitude of material responses. In order to properly study these microstructural
and size-scale effects, artifacts from factors such as surface roughness must be
mitigated. Due to the variations in the scale of microstructure, it is helpful to have
a variety of techniques that can be applied over a range of length scales to provide
benchmarks and advance our understanding of microscale mechanical behavior.
4 Sample Size Effects on Strength in René 88DT
It is well known that microstructure plays a significant role in governing the
deformation of metals and determining their mechanical properties. Examining the
microstructure at different length scales reveals unique mechanisms, such as intragranular interactions of dislocations, phase morphologies at the single crystal scale,
and interactions between neighboring grains and twins at the polycrystalline scale.
The ability to measure material properties at different length scales is critical to the
development of multiscale property prediction models. In this type of modeling, the
use of a representative volume element (RVE), which can be further characterized
as a property volume element (PVE) or microstructural volume element (MVE),
is a key building block for the multiscale framework [92, 93]. These elements
represent the volume of material that must be considered to reach a convergence
109
that each imparts. The FIB has been demonstrated to be quite useful for machining
sensitive materials or machining at length scales of tens of microns or less with high
precision and very low damage. The femtosecond laser, though still a relatively
new machining tool, has already been applied in enough cases to demonstrate its
utility in machining samples with a thickness ranging from tens of microns to a
few hundred microns, with damage scaling with laser beam energy, but able to be
controlled to less than a micron in most cases. Although wire EDM is a technique
typically applied at the macro scale, with proper optimization it can also be applied
at a scale on the order of a few hundred micrometers up to much larger scales, with
damage on the order of single-digit microns.
Understanding the capabilities of these three techniques allows a methodology
that facilitates machining of materials at multiple length scales in order to study size
effects. It can also be applied to develop sample geometries not only for microtensile
testing but for developing other microscale samples, such as microcantilevers for
studying fatigue or microbending samples for studying fracture toughness. The true
benefit of being able to apply these complimentary techniques lies in combining the
various techniques to improve the throughput of test samples in a way that has not
been achieved previously.
Developing techniques with different material-removal rates and applicable
length scales, and optimizing these techniques, is critical to the manufacture
and testing of microtensile samples. Sample quality has a significant impact on
microtensile results, especially at smaller length scales. There is an inherent
stochasticity that arises from testing materials at smaller length scales, specifically
in the single crystal and mesoscale regimes where microstructural features give rise
to a multitude of material responses. In order to properly study these microstructural
and size-scale effects, artifacts from factors such as surface roughness must be
mitigated. Due to the variations in the scale of microstructure, it is helpful to have
a variety of techniques that can be applied over a range of length scales to provide
benchmarks and advance our understanding of microscale mechanical behavior.
4 Sample Size Effects on Strength in René 88DT
It is well known that microstructure plays a significant role in governing the
deformation of metals and determining their mechanical properties. Examining the
microstructure at different length scales reveals unique mechanisms, such as intragranular interactions of dislocations, phase morphologies at the single crystal scale,
and interactions between neighboring grains and twins at the polycrystalline scale.
The ability to measure material properties at different length scales is critical to the
development of multiscale property prediction models. In this type of modeling, the
use of a representative volume element (RVE), which can be further characterized
as a property volume element (PVE) or microstructural volume element (MVE),
is a key building block for the multiscale framework [92, 93]. These elements
represent the volume of material that must be considered to reach a convergence