The effect of superelastic strain on the damping capacity in columnar-grained Cu-Al-Mn shape memory alloy

Abstract

Columnar-grained Cu-Al-Mn shape memory alloy (SMA) can experience high superelastic strain exceeding 7% and exhibits a nearly 100% superelastic recovery ratio due to its straight grain boundaries and strong texture along the solidification direction, which allows it to reach the strain level of a single crystalline Cu-based or Ni-Ti SMAs and possesses a potential for damping applications. In this paper, the damping capacity of Cu-Al-Mn SMA in various deformation conditions during a strain-controlled superelastic cyclic tensile process was studied. The anisotropy characteristics and the cyclic effect of damping capacity were analysed. The damping capacity of columnar-grained Cu-Al-Mn SMA increases as the loading strain increases in superelastic tensile processes, and a large damping capacity anisotropy occurs. At low loading strain (<6%), T-45° sample (45° is the angle between the loading direction and the axis of columnar grains) has the largest energy dissipation per unit recovery strain, ΔW1%, due to its high-stress level. At high loading strain (>6%), T-0° and T-15° samples can achieve a good damping capacity because of high superelasticity and plasticity. In addition, the damping capacity of columnar-grained Cu-Al-Mn SMA along the solidification direction has a significant cyclic effect. At the same loading strain (4%–10%), ΔW1%, and loss angle, ΔW/2πW first decrease to the minimum, then increase to the maximum and, finally, decreases as the number of cycles increases. The minima and maxima of ΔW1% and ΔW/2πW at different strain amplitudes correspond to the similar residual strain ratio, εr/εt. The change curves of damping capacity related to εr/εt can be divided into three stages: the stable damping capacity stage with low residual strain; the rapidly increasing damping capacity stage; the sharp cumulative stage of residual martensite with limited values of strain damping capacity.