Investigation On Structures And Physicalproperties Of Zrand Rh-Zr Intermetallics Based On First-principle Calculation

This dissertation is devoted to the exploration of the structures and properties of thetransitional metal Zirconium and Rh-Zr intermetallics through first-principle calculationsbased on density functional theory. The performance of materials determines its capability,thus on the designing and application of Zr and Zr alloys, it is of great significance tosystematically, clearly and accurately describe the characteristic and explore themicroscopic nature.Firstly, three phases of Zr are modeled and optimized, the equilibrium geometry, totalenergy and elastic moduli are obtained. In the thermodynamic point of view, the stabilityof each phase is analyzed and the transition pressures are calculated. Furthermore, thereason of phase transition is discussed in the sight of electronic structure, and the pressurerange where the phase being stable is given. In this part, we get the experimental trend of acrystallographic sequence and the transition pressure agreed qualitatively withexperiments, and point out that phase transition has much relation with the density ofstates at Fermi level. The dependence of electron populations with pressure is obtained.Having the equilibrium structures, we then take the environment factor intoconsideration. The emphasis is put on the mechanical properties of Zr under hypostaticpressure and homogeneous deformation, and the effection of temperature and/or pressureon thermodynamics. The main contents are the followings: the variation with pressure ofstructure, elastic constants, elastic modulus, sound velocity, elastic anisotropy,ductility/brittleness; the ideal tensile/compressive/shear strength and the correspondingstrain; the dependence with pressure and temperature of the thermodynamc parametersincluding reduced volume, bulk modulus, heat capacity, Debye temperature and thermalexpansion coefficient; and the comparasion of the performance between different phasesand analyzing the underlying reason. This work presents lots of data for Zr, shows the highelastic moduli, low elastic anisotropy and high ideal strength of omega Zr to the hcp Zr,and finds out the fundamental cause in different properties of various crystal phases. Theendings provide references for application for Zr and guidelines to design Zr alloys. Combining the advantages of Rh and Zr with the demand of industry, one cansuppose Rh-Zr system will play an important role in superalloy. Bearing this, we giveinvestigations on this system. Starting with the eleven RhxZrystructures reported in theliterature, we built and optimize the models. The obtained equilibrium structures are ingood agreement with available results. Furthermore, the mechanical properties and theelectronic structure are demonstrated. The major work is to analyze the stability of eachcompound from the points of thermodynamics, mechanical and electronic, then tell out thestable structures, resolving the existing contradiction on the stable RhxZryintermetallics.At last, basic investigation on exloring superalloy with Rh-Zr system is given.Considering the crucial roles of the matrix and the precipitate, i.e. fcc Rh and L12Rh3Zr,the structure, mechanical properties, electronic structures and thermodynamic propertiesare systematically studied. We pay attention to the difference of the two phases andillustrate that the affection on the alloy of the ratio between them. This work will behelpful to develop the superalloy with Rh-Zr system.