Deformation of as-fabricated and helium implanted 100 nm-diameter iron nano-pillars

〈101〉-oriented cylindrical single crystalline Fe samples with diameters of 100. nm and heights of 1. μm were implanted with 0.36±0.06. at% helium throughout their gauge sections. Uniaxial deformation experiments revealed a 40% higher yield and ultimate strengths in tension and a 25% higher yield strength and flow stress at 10% plastic strain in compression for implanted samples compared with as-fabricated ones. Observed tension-compression asymmetry in implanted pillars was attributed to the non-planarity of screw dislocation cores and to twinning-antitwinning deformation typical of bcc metals and the interaction between dislocations and He bubbles. Compressive stress-strain data in both sets of samples had three distinct regimes: (1) elastic loading followed by (2) discrete strain bursts during plastic flow with significant hardening up to strains of 5%, and (3) "steady state" discrete plasticity characterized by nearly-constant average flow stress. Each regime is discussed and explained in terms of competition in the rates of dislocation multiplication and dislocation annihilation.