Effect of orientation and loading rate on compression behavior of small-scale Mo pillars

Recently, much work has focused on the size effect in face centered cubic (fcc) structures, however few pillar studies have focused on body centered cubic (bcc) metals. This paper explores the role of bcc crystal structure on the size effect, through compression testing of [001] and [235] Molybdenum (Mo) small-scale pillars manufactured by focused ion beam (FIB). The pillar diameters ranged from 200 nm to 5 mu m. Results show that the relationship between yield stress and diameter exhibits an inverse relationship (sigma(y) alpha d(-0.22) for [001] Mo and sigma(y) alpha d(-0.34) for [235] Mo) weaker than that observed for face centered cubic (fcc) metals (sigma(y) alpha d(-0.6 to -1.0)). Additional tests at various loading rates revealed that small-scale Mo pillars exhibit a strain rate sensitivity similar to bulk Mo. (C) 2009 Elsevier B.V. All rights reserved.