Novel Technique for Assesment of Materials Behavior


	Steven J Polasik B.S.E Arizona State University (2001) M.S. The Ohio State University (in progress) polasik.1@osu.edu (614) 688-3409 Advisors: Dr. Hamish Fraser & Dr. Michael Mills
Research Assesment of Materials Behavior via FIB and MEMS-based Characterization Methods Supported by: AFRL
By utilizing novel techniques such as the Focused Ion Beam (FIB) and nanoindenter systems, we are able to perform small-scale mechanical behavior testing on individual grains within a material. Specifically, we machine and test the specimen in compression. There are various benefits to small-scale mechanical behavior testing: No need to grow single crystals Test specimen have the same impurity content, composition, and microstructure as found in the real engineering alloy

		As shown in the accompanying figure, the ability to perform mechanical behavior experiments on individual grains has the potential to provide data to predict the aggregate, or bulk, response of an alloy. Before this will be feasible, however, we must understand the size effects, if any, in our target material system.
The current material systems under investigation are: Ti-6Al, Ni₃Al (0.2Hf), Ni, and a binary Ni₃Al alloy. All of these systems are tested as single crystals (or as a single colony in the case of the binary alloy) in order to captilize on bulk single crystal compression data.
The Dual Beam FIB (DB-FIB) essentially combines a Scanning Electron Microscope (SEM) with a Focused Ion Beam (FIB) microscope, providing us with both high resolution imaging and precision micromachining. Therefore, we can ion machine micron-scale 3-D structures that serve as test specimen. On the right is an image of a typical micropillar. for this particular pillar, the diameter is 20 microns. The trench not only defines the pillar, but also allows room for the compression platen. The fiducial mark is used by the visual recognition portion of the automation process.

Six examples of typical micropillars are shown below with the respective diameters given. The length:diameter ratio is 2:1.

A standard nanoindenter system is used as the compression device. However, one important modification is the substitution of a flat tip instead of the standard Berkovitch tip. The bulk sample is aligned to the flat tip by means of a custom tilt stage within the nanoindenter enclosure. This ensures the compression axis is along the length of the micropillar. Typical results exhibiting the evidence of single slip (via slip lines) are shown below.

Presently, we are using the Transmission Electrom Microscope (TEM) to perform dislocation analysis on the compressed pillars. Further details and results coming soon. Links