The Structural Configurations And Elastic Properties Of Ordered And Disordered Ti Alloys From First-principles

?-type Ti alloys have been widely used in biomedical and aerospace fields as ideal Ti alloys with high strength and low modulus due to their advantages of low elastic modulus,good formability and deformation hardening.Nb is a strong?stabilizer.Thus,it is significant to study the phase stability and elastic properties of TiNb-based alloys.In this thesis,the structural properties and elastic properties of TiNb and TiNb-TM(TM=Mo,Ta,Zr)alloys have been investigated via the ordered and disordered methods based on first-principle calculation.The occupation preference of oxygen in TiNb binary alloy and the elastic properties of O-doped structures have also been studied.Binding energy calculation results showed that the increase of cell size does not improve the stability of the disordered structures.And the disordered structures get higher stability under the same 2×2×2 supercell size.In terms of TiNb-based ternary alloys,the structural stability in descending order is:Mo>Ta>Zr.The elastic calculation showed that the elastic stability in descending order is:Mo>Ta>Zr.The 3×3×3 supercell performed better than 2×2×2 supercell in elastic properties.And the transition atoms located at face-centered and body-centered sites could make ordered structures more stable.The type of alloying elements has a weak effect on the elastic modulus.In general,ordered structures with regular configurations may get lower elastic modulus.Through a symmetry-based projection technique,we established that this kind of projection approach is applicable for TiNb-based alloys and can be used to evaluate different disordered structures.Compared to disordered structures,the anisotropy of ordered structures were affected greatly by the type of alloying elements,and the TiNbZr performed most serious.It can be found that disordered structures performed well in predicting the anisotropy of TiNb and TiNb-TM alloys by analyzing the anisotropic variables along[100],[010],[001]orientations.According to the calculation results of O-doped TiNb binary alloys,oxygen atoms in TiNb binary cell tend to exist in octahedral position on the surface of the cell.Besides,the impact on (?)12 and (?)44 from different O-occupations plays an important role in the elastic stability of TiNb alloy.And doping TiNb with oxygen atoms will reduce the elastic stability of the system.The site preference of oxygen is one of the factors influencing the elastic modulus of Ti alloy.A small amount of doped oxygen atoms may reduce the elastic modulus of Ti alloy while maintaining the stability of the system.