Tech Briefs

Scientists employ focused ion beam milling to prepare micron-size single-crystal test specimens and use a nanoindenter device to record stress-strain curves.

Scientists from AFRL, Pratt & Whitney Aircraft, and General Electric Aircraft Engines, working under the Defense Advanced Research Projects Agency's Accelerated Insertion of Materials (AIM) program, have invented a new method for characterizing the single-crystal properties of aerospace alloys using micron-size test samples. The research team based the new characterization method on focused ion beam (FIB) microscopy and a commercially available nanoindentation-based test instrument. Further development of these methodologies, in conjunction with their continued integration with simulation methods devised under the AIM program, will enable engineers to consider local changes in material microstructure and their effect on properties in the design process. The integration of advanced mechanical property measurements, materials representation, and simulation methods will dramatically decrease the time required for new materials insertion and will transform microstructure into a design variable for engineered systems. These advancements will directly benefit combat systems and readiness.

A deformed single crystal of pure nickel after measurement of critical resolved shear stress under single-slip conditions
A primary challenge to the rapid insertion of new materials into the design cycle is the need to understand both the intrinsic properties of an engineering material at the microscopic level and the influence of defects on these properties at the macroscopic level. Historically, scientists have been unable to develop model parameters or validate continuum materials behavior models that are based upon discrete microstructural information. Continuum crystal plasticity models are at the frontier of techniques that incorporate direct microstructural information. However, a major deficiency of these models is the need to obtain required input information: the single-crystal mechanical properties of individual grains, or microconstituents. Acquiring this information is particularly difficult when such parameters must reflect the subtleties of material process history or the local influence of material defects.