Creep of micron-sized Ni3Al columns

The Strength of Submicron-Sized Materials

“…Here, the creep deformation seems to happen by viscous material flow at the pillar top, and no crystallographic features such as slip traces can be observed. Furthermore, by comparing the pillar creep rates at two applied stresses, the stress exponent was found to be close to unity 25 , in agreement with the nanoindentation results shown in fig. 5 for the smallest indents on flat surfaces.…”

“…6 shows a more direct experiment to demonstrate the creep behaviour of a submicron specimen. Here, a FIB-fabricated Ni 3 Al micro-pillar was crept by applying compressive pressure on the head of the pillar using a nanoindentation tip 25 . The pillar was initially deformed by a few cycles of load ramp to inject dislocations into the crystal, and then the load was held at a peak value for 100s to monitor the creep response.…”

The mechanical size effect as a mean-field breakdown phenomenon: Example of microscale single crystal beam bending

“…In bulk plasticity this assumption is justifiable as the Taylor stress scales with the square root of the dislocation density and so does the bow-out stress for a source when the pinning points are of the same order of magnitude as the mean dislocation spacing. However, in confined probe geometries, it is possible that multiplication rates are not high enough to maintain an imposed shear rate as the source activation stress scales inversely with size [27,[45][46][47][48]. The Orowan equation as written here, therefore, maps the kinematic necessity that an imposed velocity gradient (here in scalar formulation) must be accomplished by dislocation slip, which has to be permanently replenished by a limited set of sources in the case of small samples.…”

Novel methods for micromechanical examination of hydrogen and grain boundary effects on dislocations

“…Utilizing this simplified pillar geometry, researchers have extensively studied the size-dependent flow stress of single crystal micropillars using a flat-punch indenter as a compression testing machine [21][22][23][24]. The size effect has been investigated in numerous materials including Ni [25,26], Cu [27][28][29][30][31][32][33], Mo [34][35][36][37][38][39], NiTi shape memory alloy [40], Ni 3 Al [41], oxide dispersed alloy [42], Au [23,24,43,44], nanoporous Au [45,46], ceramics [47][48][49] and semiconductors [50][51][52][53]. However, the ease and flexibility with which micropillars can be produced provide further exciting possibilities for new studies aside from the size effect.…”