Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadía, E-31006 Pamplona, Spain.
J Phys Condens Matter. 2010 Apr 28;22(16):166001. doi: 10.1088/0953-8984/22/16/166001. Epub 2010 Apr 6.
The influence of long-range L2(1) atomic order on the martensitic and magnetic transformations of Ni-Mn-Ga shape memory alloys has been investigated. In order to correlate the structural and magnetic transformation temperatures with the atomic order, calorimetric, magnetic and neutron diffraction measurements have been performed on polycrystalline and single-crystalline alloys subjected to different thermal treatments. It is found that both transformation temperatures increase with increasing atomic order, showing exactly the same linear dependence on the degree of L2(1) atomic order. A quantitative correlation between atomic order and transformation temperatures has been established, from which the effect of atomic order on the relative stability between the structural phases has been quantified. On the other hand, the kinetics of the post-quench ordering process taking place in these alloys has been studied. It is shown that the activation energy of the ordering process agrees quite well with the activation energy of the Mn self-diffusion process.
研究了长程 L2(1)原子有序对 Ni-Mn-Ga 形状记忆合金马氏体相变和磁相变的影响。为了将结构和磁转变温度与原子有序相关联，对经过不同热处理的多晶和单晶合金进行了量热法、磁和中子衍射测量。结果发现，两种转变温度都随原子有序度的增加而升高，与 L2(1)原子有序度的程度呈完全线性关系。建立了原子有序度与转变温度之间的定量关系，由此量化了原子有序度对结构相相对稳定性的影响。另一方面，研究了这些合金中淬火后有序化过程的动力学。结果表明，有序化过程的激活能与 Mn 自扩散过程的激活能非常吻合。
