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采用第一原理计算方法系统地研究了Cu含量对Ni-Mn-Ga-Cu铁磁形状记忆合金的晶体结构、相稳定性和磁性能的影响。形成能的计算结果表明,在Ni2MnGa合金中,添加的第四组元Cu将优先占据Mn的亚晶格格点,从而为实验中的成分设计提供了理论依据。随着Cu含量的增加,铁磁性奥氏体的相稳定性逐渐减弱,而顺磁性奥氏体的相稳定性则逐渐增强,导致顺磁性奥氏体和铁磁性奥氏体的基态总能量之间的差值减小,这是此类合金Curie温度TC随Cu含量的增加而降低的本质原因。而实验上观察到的马氏体相变温度Tm随合金元素Cu含量的增加而升高的现象本质上是由于奥氏体与马氏体两相之间的能量差增大,从而提高了马氏体相变的驱动力所致。此外,Ni-Mn-Ga-Cu合金的磁性能随Cu含量的增加而减弱,并从电子态密度的角度阐释了磁性能降低的原因。
The influence of Cu content on the crystal structure, phase stability and magnetic properties of Ni-Mn-Ga-Cu ferromagnetic shape memory alloy has been investigated systematically using first-principle calculation method. The formation energy calculations show that in the Ni2MnGa alloy, the fourth element Cu added will preferentially occupy the subgrain lattice point of Mn, which provides a theoretical basis for the experimental composition design. With the increase of Cu content, the phase stability of ferromagnetic austenite gradually decreases and the phase stability of paramagnetic austenite gradually increases, resulting in the total ground state energy of paramagnetic austenite and ferromagnetic austenite The difference between the decrease, which is the nature of the Curie temperature TC TC with the increase of Cu content decreases. The experimentally observed martensitic transformation temperature Tm with the alloying element Cu content increased phenomenon is essentially due to the increase of the energy difference between the two phases of austenite and martensite, thereby increasing the horse The driving force of the martensitic transformation. In addition, the magnetic properties of Ni-Mn-Ga-Cu alloy decrease with the increase of Cu content, and the reasons for the decrease of magnetic properties are explained from the electronic density of states.