Composition dependent elastic modulus and phase stability of Ni_2MnGa based ferromagnetic shape memory alloys

作     者：HU QingMiao LUO HuBin LI ChunMei VITOS Levente YANG Rui 

作者机构：Shenyang National Laboratory for Materials ScienceInstitute of Metal ResearchChinese Academy of SciencesShenyang 110016China Applied Materials PhysicsDepartment of Materials Science and EngineeringRoyal Institute of TechnologyStockholm SE-10044Sweden Condensed Matter Theory GroupPhysics DepartmentUppsala UniversityUppsala SE-75120Sweden Research Institute for Solid State Physics and OpticsP.O.Box 49Budapest H-1525Hungary 

出 版 物：《Science China(Technological Sciences)》 (中国科学（技术科学英文版）)

年 卷 期：2012年第55卷第2期

页      面：295-305页

核心收录：

学科分类：081504[工学-水利水电工程] 08[工学] 0815[工学-水利工程] 080502[工学-材料学] 0805[工学-材料科学与工程（可授工学、理学学位）] 

基　　金：supported by the MoST of China (Grant No. 2011CB606404) the National Natural Science Foundation of China (Grant No. 50871114) 

主　　题：NieMnGa martensitic transformation elastic modulus phase stability density functional theory 

摘      要：Ni2MnGa based ferromagnetic alloys are ideal candidates for applications such as actuators, magnetic refrigerators or magne-tostrictive transducers due to their attractive properties such as magnetic field induced shape memory effect and large magnetocaloric effect. The properties of these alloys （e.g., the martensitic transformation temperature TM） sensitively depend on the composition. Understanding the composition dependence of these properties so as to design the alloy as desired is one of the main research topics in this area. In recent years, we have investigated the composition dependent elastic modulus and phase stability of Ni2MnGa-based alloys by using a first-principles method, in hope of clarifying their connection to the properties of these alloys. In this article, we review the main results of our investigations. We show that the tetragonal shear modulus C＇ is a better predictor of the composition dependent TM than the number of valence electrons per atom （e/a） since the general TM-C＇ correlation works for some of the alloys for which the TM-ela correlation fails, although there exist several cases for which both the general TM-C＇ and TM-ela correlations break down. Employing the experimentally determined modulation function, the complex 5-layer modulated （5M） structure of the martensite of Ni2MnGa and the Al-doping effect on it are studied. We find that the shuffle and shear of the 5M structure are linearly coupled. The relative stability of the austenite and the marten- sites is examined by comparing their total energies. The non-modulated martensite β＇″ with the tetragonality of the unit cell c/a〉1 is shown to be globally stable whereas the 5M martensite with c/a〈1 is metastable. The critical Al atomic fraction over which the martensitic transformation between the 5M martensite and austenite cannot occur is predicted to be 0.26, in reason- able agreement with experimental findings.