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  • Key Factors Achieving Large...
    Peng, Huabei; Chen, Jie; Wang, Yongning; Wen, Yuhua

    Advanced engineering materials, March 2018, Volume: 20, Issue: 3
    Journal Article

    Fe–Mn–Si‐based shape memory alloys are the most favorable for large‐scale applications owing to low cost, good workability, good machinability, and good weldability. However, polycrystalline Fe–Mn–Si‐based shape memory alloys have low recovery strains of only 2–3% after solution treatment, although monocrystalline ones reach a large recovery strain of ≈9%. This review gives an overview of the improvement of recovery strains for polycrystalline Fe–Mn–Si‐based shape memory alloys. It is proposed that two fundamental aspects, that is, composition design and microstructure design, shall be satisfied for obtaining large recovery strains of above 6%. Alloying compositions determining the ceiling of recovery strains shall follow three guidelines: (i) Si content is 5–6 wt%; (ii) 20 wt% ≤ Mn ≤ 32 wt%; (iii) addition of elements strongly strengthening austenite matrix. Microstructure design includes coarsening austenitic grains and reducing twin boundaries as far as possible together with introducing a high density of stacking faults and second phases of strengthening austenite. Low cost Fe–Mn–Si‐based shape memory alloys are suitable for large‐scale applications. However, their recovery strains are only 2–3% in solution‐treated polycrystalline status. This review summarizes the origin of shape memory effect and the improvement history of recovery strains. It is concluded that two fundamental aspects, that is, composition design and microstructure design, shall be followed to achieve a large recovery strain of above 6%.