Orientation dependence in superelastic Cu-Al-Mn-Ni micropillars

Abstract

The superelastic behavior of single crystal Cu-Al-Mn-Ni shape memory alloy micro-pillars was studied under compression as a function of crystallographic orientation. Cylindrical pillars of about 2 μm diameter were micro-machined from targeted crystal orientations. While pillars oriented close to the [001] direction showed the largest total transformation strain (~7%), plastic deformation dominate d the compressive response in the pillars milled close to the [111] direction due to their high elastic anisotropy combined with the large stresses required to induce th e transformation. Shape strain contour plots were constructed for γ’ and β’ martensites, and the martensite start stress was calculated using the Clausius-Clapeyron equation. The same general trends are observed in both the experimental and calculated results, with some exceptions: larger transformation stresses and lower transformation strains are observed in the microsized pillars.