First-principles Study Of The Electrical,Mechanical And Thermodynamic Properties Of A Novel MAX Phase Material Hf₂PB

MAX phase material is a kind of layered compound with excellent properties of metal and ceramics simultaneously,which can be used in the extreme environment of high temperature,high pressure and high radiation.MAX phase material has been considered to be one of the candidates of structure materials working in the next generation fusion reactor.In order to ensure the service life of the fusion reactor,the MAX phase as structural materials must be able to maintain mechanical integrity and dimensional stability under extreme radiation,high temperature,high corrosion and high stress.Therefore,MAX phase material must have good physical properties of anti-radiation expansion and good mechanical properties at room temperature and high temperature.In this paper,the first principle calculation method based on density functional theory(DFT)was employed to study the new MAX phase material Hf2PB.The performance of Hf2PB improved by X-site solid solution doping,and the effects of defects and impurities on the performance of the radiation environment were studied.The main research contents and results are as follows:1 The crystal structures,electronic structures and mechanical properties of the solid solution Hf2PB1-xMx with C and N doped in B were studied.The results show that the lattice constants of solid solutions decrease with increasing C/N doping concentration.Hf2PB and its solid solutions show good metallicity properties.The elastic constants and elastic modulis of Hf2PB and its solid solutions increase with the doping concentration.As the doping concentration increases,the hardness of the solid solution first increases and then decreases.The doping concentration has little effect on the plasticity,mechanical processability,and anisotropy of the solid solutions.Thermodynamic studies have found that the Debye temepratures of Hf2PB and its solid solutions are very high,which indicates that they are very good thermal conductive materials.2 The effects of three kinds of vacancy defects on the geometry,electronic structures and mechanical properties of Hf2PB were studied.The results show that three kinds of point defects reduce the volume of Hf2PB.The Hf2PB with vacancy defects is judged to be more metallic in view of the values of DOS at Fermi level.All kinds of vacancy defect cause Hf2PB elastic constants,elastic moduli and hardness to decrease,but have little effect on plasticity and anisotropy.3 The influence of impurity H atom on the geometry,electronic structure and mechanical properties of Hf2PB was studied.H acting as an impurity instead of P and B reduces the elastic constants,elastic modulus,and hardness of Hf2PB,but enhances its plasticity,while H-substituted Hf impurities cause Young’s modulus E and shear modulus G to increase,and plasticity decreases.Point defects can reduce the mechanical properties of Hf2PB,but they played a positive role on its metallicity.