Regulation Of TiNb Alloy Magnetism By Applied Strain And Element Doping

The metastableβTi-Nb alloy has the advantages of low elastic modulus,good corrosion resistance and biocompatibility,which shows a broad application prospect in the field of biomedical materials.As a bone implanting material,its magnetic property has an important effect on nuclear magnetic resonance imaging and the differentiation and growth of cells around the implanting material.Recently,our research group analyzed the electronic structure of Ti-Nb alloy,and found that strong magnetic coupling occurs between the Ti and Nb atoms of the two collinear bonding inβ-Ti_0.75Nb_0.25alloy,resulting in it exhibits magnetism.Moreover,the experiment measurement also confirmed the alloy was weakly magnetic.However,the magnetic intensity of the alloy measured by the experiment is much weaker than the theoretical prediction value.Therefore,in the present thesis,the origination of the magnetism ofβ-Ti_0.75Nb_0.25alloy was further investigated by using the first principle method based on density functional theory.The effects of external strain and Fe、Mo、Zr additions on the magnetic properties ofβ-Ti_0.75Nb_0.25alloy were also.Its main research contents and results are as follows:（1）All possibleβ-Ti_0.75Nb_0.25crystal structures were constructed,and their energy and magnetism were calculated and analyzed to reveal the origin ofβ-Ti_0.75Nb_0.25magnetism.It is found that,for a super crystal cell with 16 atoms,β-Ti_0.75Nb_0.25have 18 crystal structures,and four of them are of magnetism,which are in high energy status.DO₃structure has the highest magnetic moment,in which the arrangement of atoms is the most ordered.In the DO₃structure,the Ti atom collinear bonding with Nb exhibits the largest magnetic moment due to strong magnetic coupling between the two atoms,leading to the magnetism of theβ-Ti_0.75Nb_0.25.（2）The effects of the applied uniaxial tension and compression strains and hydrostatic strains on energy and magnetism ofβ-Ti_0.75Nb_0.25were analyzed using a first principles method based on density functional theory.The results show that,the application of uniaxial tension and compression strains of 1-3%to the alloy along the<100>can reduce the energy of the alloy with magnetic structure,thus increasing the probability of magnetic structure.The application of an uniaxial compression strain can reduces the overall magnetic moment of the alloy slightly,while the application of the uniaxial tension strain can promote the overall magnetic moment of the alloy.The application of hydrostatic strain has little impact on the energy of the alloy with all structures,but it can lead to a substantial decrease in the overall magnetism of the alloy.（3）The effect of Fe,Mo and Zr element additions on the energy and magnetism ofβ-Ti_0.75Nb_0.25alloy was studied by using the first principle method based on density functional theory.The results show that the additions of the three elements have no significant effect on the relative energy of the 18 structures.However,Zr additions can reduce the magnetic moment of DO₃structures and reduce the magnetic moment of the other three magnetic structures to 0.While the additions of Fe and Mo can lead to the complete disappearance of the magnetism of the 18 structures.