Abstract The effect of combined mechanical and thermal treatments in the magnetostructural properties was studied in Ni-Mn-Sn metamagnetic shape memory alloys, in which the extraordinary high stability of the L2 1 structure precludes the variation of atomic order by means of conventional thermal treatments. A Ni 50 Mn 35 Sn 15 alloy has been mechanically milled and then annealed at different temperatures in order to produce different microstructural states. The evolution of both the internal stresses and the crystallite size upon annealing has been quantified and correlated to the evolution of the martensitic transformation features and the magnetic properties. It is found that the relaxation processes brought by annealing leads to recovery of the martensitic transformation and the enhancement of the magnetism at both macroscopic and local level. In particular, the density of non-magnetic inclusions (defects) and their stress field decrease upon annealing, thus leading to an increase of the saturation magnetization and a decrease of the martensitic transformation temperature range, respectively, which results in a higher magnetocaloric effect. The obtained results confirm that, once the transition temperature has been fixed by the composition, the modification of the microstructure through thermomechanical treatments appears as the best way to tune the functional properties of these alloys.

中文翻译：

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Ni-Mn-Sn变磁形状记忆合金缺陷与磁结构性能的相关性

摘要 在 Ni-Mn-Sn 变磁形状记忆合金中研究了机械和热处理联合处理对磁结构性能的影响，其中 L2 1 结构的极高稳定性排除了通过常规热处理引起的原子序的变化。Ni 50 Mn 35 Sn 15 合金经过机械研磨，然后在不同温度下退火，以产生不同的微观结构状态。退火时内应力和微晶尺寸的演变已被量化并与马氏体转变特征和磁性的演变相关联。发现退火带来的弛豫过程导致马氏体转变的恢复和宏观和局部水平的磁性增强。特别是非磁性夹杂物（缺陷）的密度及其应力场在退火时降低，从而分别导致饱和磁化强度增加和马氏体转变温度范围减小，从而导致更高的磁热效应。获得的结果证实，一旦转变温度由成分固定，通过热机械处理改变微观结构似乎是调整这些合金功能特性的最佳方式。