Outstanding intrinsic two-way shape memory effect of the Ni54.71Mn22.14Ga23.15 oligocrystalline shape memory microwire

Abstract

The shape memory effect of the Ni54.71Mn22.14Ga23.15 oligocrystalline microwire was investigated. The microwire was expected to exhibit an outstanding two-way shape memory effect due to the directional internal stress induced in the preparation. The results show that the microstructure of the as-prepared Ni54.71Mn22.14Ga23.15 microwire was mainly oriented martensites at room temperature. An intrinsic two-way shape memory strain of 8.8% (±0.2%) in the as-prepared microwire was acquired in the process of cooling and heating with no applied stress. A shape memory strain of 14.4% (±0.2%) was obtained under the constant stress of 10 MPa. The isothermal tensile tests were carried out on the microwire in the temperature range of 383–463 K and the recoverable tensile strains were over 13%. The microwire after superelastic training maintained a two-way shape memory strain of 7.3% (±0.2%) and a work output of 31 J/cm3. The shape memory effect of the microwire in this work displays prominent advantages in the reported shape memory alloys, mainly in the aspects of larger intrinsic shape memory strain and higher work output under relatively lower stress with the operating window around room temperature.