Nanoscale compression testing inside a TEM

The technique of micro-pillar compression testing is quickly becoming a new paradigm for small-scale mechanical testing (1). In particular, micro-pillar compression testing is an effective technique for examining size effects at small length scales and investigating materials that are difficult to make in bulk quantities. Through quantitative in situ nano-compression tests in a transmission electron microscope (TEM) we can directly correlate the dynamic deformation mechanisms in submicron pillars with simultaneous measurement of the imposed stresses. This talk will demonstrate this capability through the in situ compression of focused ion beam (FIB) machined metallic pillars with diameters between 150 and 400 nanometers. In pure, single crystal Ni pillars, the phenomenon of source-limited deformation is evident where plasticity is derived from single or very few active slip systems(2). In a second example we have systematically investigated two AA6063 alloys with identical compositions, one as-extruded and the other heat-treated to increase the solute concentrations in the matrix. In the annealed AA6063 pillars, the deformation is more complicated and cross-slip can result in a three-dimensional dislocation network that leads to a rotation of the pillar structure under compression. We also found that the annealed sample exhibited a higher yield stress and greater deformability as compared to the as-extruded sample, similar to data from bulk mechanical tests of the same alloys. Furthermore, our dynamic observations and comparison of the two alloys demonstrate that the dislocation plasticity behavior is quite different for the two samples. Our results will show that the nanoscale plasticity behavior seen during in situ deformation relates directly to the bulk ductility of these alloys. All of these results will be shown in relation to the size effects seen in ex situ pillar compression tests where a direct relationship between the yield stress and the diameter of pillar structures has been observed.