Abstract Ni-Co-Mn-Sn Heusler alloys possess attractive multifunctional properties, owing to the unique metamagnetic shape memory effect. However, the intrinsic high brittleness limits their applications. In this work, we studied the effects of Fe doping and heat treatment on the microstructures, mechanical properties, martensitic transformation and magnetic behaviours of Ni-Co-Mn-Sn-Fe Heusler alloys. A eutectic dual-phase was successfully introduced in Ni48Co4Mn39-xSn9Fex (x = 3, 4, 5, 6, 7 and 8) alloys by doping Fe for Mn. The engineering strength and ductility increased almost by twofold in a eutectic dual-phase alloy compared to the single-phase alloy. Such microstructure also shows a large quasilinear pseudoelasticity of 4.3% with a very small stress hysteresis and good cyclic stability. After the heat treatment, the γ phase lamellae was much coarsened which resulted in decrease of strength and ductility by ~20%. The magnitude of pseudoelasticity decreased to 2.6% and worse cyclic stability occurred because of the grain coarsening. The metamagnetic transformation was obtained when Fe content is between 2.5 at% and 6.5 at%, with Fe3 alloy showing a A(ferro) ⇔ M(para) type and Fe4-Fe6 alloys showing a A(ferro) ⇔ M(ferro) one.

中文翻译：

---

双相Ni-Co-Mn-Sn-Fe铁磁形状记忆合金的马氏体相变行为和力学性能

摘要 Ni-Co-Mn-Sn Heusler 合金由于具有独特的变磁形状记忆效应而具有吸引人的多功能特性。然而，固有的高脆性限制了它们的应用。在这项工作中，我们研究了 Fe 掺杂和热处理对 Ni-Co-Mn-Sn-Fe Heusler 合金的显微组织、力学性能、马氏体转变和磁行为的影响。通过为 Mn 掺杂 Fe，成功地在 Ni48Co4Mn39-xSn9Fex（x = 3、4、5、6、7 和 8）合金中引入了共晶双相。与单相合金相比，共晶双相合金的工程强度和延展性几乎增加了两倍。这种微观结构还显示出 4.3% 的大拟线性伪弹性，具有非常小的应力滞后和良好的循环稳定性。热处理后，γ 相片晶粗化很多，导致强度和延展性降低约 20%。由于晶粒粗化，伪弹性的大小下降到 2.6%，循环稳定性变差。当 Fe 含量在 2.5 at% 和 6.5 at% 之间时，发生变磁转变，Fe3 合金显示 A(ferro) ⇔ M(para) 型，Fe4-Fe6 合金显示 A(ferro) ⇔ M(ferro) 1 .