Comparison of shape memory properties between Cu-12.5Al–3Mn and Cu-12.5Al–3Mn–1Ni produced by additive manufacturing technology

Abstract

In this work, two Cu–Al–Mn shape memory alloys (SMAs), Cu-12.5Al–3Mn and Cu-12.5Al–3Mn–1Ni, were prepared by wire arc melting deposition, and their shape recovery rates, ultimate recoverable strains, additive manufacturing microstructures, memory recovery behaviors, and phase transition properties were comparatively investigated. Meanwhile, the mechanism of Ni in these two alloys was discussed by combining the differences in phase composition of the two alloys. Results showed that the shape recovery rate of Cu-12.5Al–3Mn alloy decreased linearly with increasing pre-strain, from 91.23% at 4% pre-strain to 62.41% at 10% pre-strain, and its ultimate recoverable strain was approximately 7%; while the shape recovery rate of Cu-12.5Al–3Mn–1Ni SMA was 100% at 4%–8% pre-strain, and remained at 96.57% until the pre-strain was increased to 10%, i.e., the recoverable strain was more than 9%. In addition, the phase change temperature of the alloy with Ni addition decreased compared to that of the alloy without Ni addition, especially the temperature hysteresis was narrower. The results indicate the formation of a new κ phase after adding Ni to the alloy. The pinning effect of this new phase significantly improves the order of martensite within the alloy. Moreover, Ni also induces the transformation of the alloy, inhibiting the precipitation of the brittle phase γ2 and leading to a marked increase in the shape memory recovery rate and the recoverable strain of the additively fabricated Cu–Al–Mn alloy. Note that Ni transforms the alloy from hyper-eutectoid components to eutectoid components. Moreover, after adding Ni, the thermoelastic martensite phase transition temperature and temperature hysteresis decreased together with its eutectoid temperature, which made the additive manufacturing Cu–Al–Mn SMA exhibit an explosive response behavior.

Keywords

• Cu–Al–Mn alloy
• Shape memory properties
• Ni element
• Additive manufacturing
• Powder core wire