Compressive-tensile deformation of nanocrystalline nickel at high pressure and temperature conditions

Abstract

We conducted uniaxial compressive and tensile deformation on nanocrystalline Ni at a confining pressure of 6 GPa and temperatures up to 900 °C. The determined compressive yield strength is 0.8 GPa, identical to the tensile yield strength obtained in the same deformation experiment, indicating that the Bauschinger effect is absent in nanocrystalline Ni. The yield strength obtained at 6 GPa is also comparable to that at ambient pressure, suggesting that the dislocation-mediated mechanisms are no longer activated during plastic deformation. Based on peak intensity and peak width analyses, grain rotation and grain growth are main factors underlying the plastic deformation.

Transformation from slip to plastic flow deformation mechanism during tensile deformation of zirconium nanocontacts

“…The deformation region observed in this study was smaller than several atom width and as a result, plastic flow deformation, which is different from well-known deformation observed in bulk states, such as slip, shear band in glass, and phase transformation 1 2 3 4 5 6 7 8 , was observed. Thus, the result shows that the well-known deformation mechanism is not activated due to size reduction to this size.…”

“…The average strain rate in this experiment was 1.4 × 10 −2 /s, which is 10 2 –10 3 times larger than those in the deformation tests of nanometer-grained polycrystalline metals 2 7 . However, the strain rate equipped in an immense amount of contact-retraction experiments of NCs via mechanically controllable break junction methods and scanning probing methods is furthermore at least 100 times larger than that in this experiment 34 .…”

“…As the size of metals decreases to the nanometer scale, dislocation motion is suppressed, or even absent, while applying external forces. When the grain size of polycrystalline metals is decreased to 10–100 nm, grain boundary sliding and grain rotation govern deformation instead of dislocation-mediated slip 1 2 3 4 5 6 7 . In particular, as the width of deformation region is reduced to several atoms, the deformation mechanism is transformed from dislocation-mediated slip to non-slip manners, i.e., homogeneous slip 8 9 10 11 12 .…”

High Pressure Phase-Transformation Induced Texture Evolution and Strengthening in Zirconium Metal: Experiment and Modeling

“…The methods used here for macroscopic stress analysis are similar to those described by ref. 25 , 26 , 27 . We first determine lattice strain, ε ( φ ) = [d 0 ( φ )−d( φ )]/d 0 ( φ ), where φ is the true azimuth angle, given by cos φ = cos θ cos χ (θ and χ are the diffraction angle and detector azimuth), and d 0 ( φ ) and d( φ ) are d-spacing values of a given lattice plane at the onset of deformation and at a certain stress state, respectively.…”