【摘要】 运用第一性原理方法计算NiTi合金三种相结构(B2、B19’和R相)的电荷密度、态密度、Mulliken布居、弹性常数,在此基础上探究NiTi合金的键合特征、弹性性质及其内在联系。计算结果表明NiTi合金主要成键类型是金属键,其次还包括共价键和离子键。离子键主要由Ti原子向Ni原子转移少量电荷形成,共价键主要由Ni-3d和Ti-3d的轨道杂化形成,此外B19’和R相中Ni-Ni原子间存在电子云重叠也具有共价键特征。弹性性质计算表明三种相结构的NiTi合金均为延性材料,并具有不同程度的弹性各向异性特征。延性强弱顺序依次为B2>R>B19’,弹性各向异性程度的强弱顺序为B19’>B2>R。材料的延脆性和弹性各向异性主要与合金中共价键、金属键的特征和强度有关。金属键具有无方向性特征,金属键越强材料的延性性能会越强;共价键具有方向性特征,共价键越强,同时金属键越弱,则材料的弹性各向异性的程度会越高。本研究揭示了NiTi合金在B2→R→B19’马氏体相变过程中键合特征和弹性性质的变化情况,对NiTi合金器械的设计和应用具有重要的参考意义。更多还原

【Abstract】 The first principle method is applied to calculate the charge density,density of states,Mulliken population and elastic constants of three phases( B2,B19’and R phase) of NiTi alloy. Furthermore,the bonding characteristics,elastic properties and intrinsic connections of different phases are investigated. The results show that there are metal bond,covalent bond and ionic bond in the NiTi alloy,and the proportion of metal bond is the largest. Ionic bond is mainly formed by charge transfer between Ti and Ni. The covalent bond is mainly formed by orbital hybridization of Ni-3 d orbit and Ti-3 d orbit,in addition,Ni and Ni share some charges to form covalent bond in B19’and R phases. The results of elastic properties show that the three phases NiTi have ductility characteristics and different degrees of elastic anisotropy. The ductility of B2 phase is higher than R phase than B19’phase and the elastic anisotropy degree of B19’is larger than B2 phase than R phase. The ductility and elastic anisotropy are mainly related to the characteristics and strength of the covalent bond and metal bond in the alloy. Due to the non-directionality characteristics of metal bond and the directional characteristics of covalent bond,the material with strong metal bond have high ductility; the material with strong covalent bond and weak metal bond have large degree of elastic anisotropy.更多还原