Investigations On The Structures And Properties Of TiAl、Zr-X (X=Ru,B,Sn) Intermetallics And Zr-Nb-Si Biomedical Alloys

In this paper, the first principles calculations have been used to study the structures and properties of TiAl, ZrRu, ZrB and Zr-Sn intermetallics. The relationships between mechanical properties and microstructures of Zr-Nb-Si biomedical alloys are also investigated. The main results are listed as follows:(1) The structural, mechanical properties and Debye temperature of doped intermetallics Ti7Al8X (X=Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W) have been investigated by employing the pseudo-potential plane-wave approach based on density functional theory. The stability of calculated structures of Ti7Al8X at 0 GPa is measured by studying mechanical stability conditions and formation energy. Mechanical properties of polycrystals are computed from values of shear modulus (G), bulk modulus (B), Young’s modulus (E), Poisson’s ratio (v) and microhardness parameter (H) for Ti7Al8X. Debye temperature of TiAl calculated using elastic data of the present work, is found to be influenced by the addition of alloying elements.(2) The site preference and alloying effects of transition-mental elements TM (TM=Ti, V, Cr, Nb, Mo, Hf, Ta, W, Rh, Pd, Os, Ir and Pt) on mechanical and electronic properties of B2 ZrRu-based compounds are investigated using density functional theory. The enthalpy of formation (Hform) and ternary transfer energy (ETM Zr�'Ru) of ZrRu-TM compounds are calculated to predict the site preference of TM. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio and other mechanical related parameters are obtained. The electronic density of states and electron density difference are calculated and the results show that the elastic properties are closely connected with the bonding strength of the compounds.(3) Density functional theory combined with quasi-harmonic Debye model is applied to research structural, mechanical and thermodynamic properties of zirconium boride. The triaxial stress-strain relations of ZrB are obtained by increasing the strain of 0.01 each step until the structure collapses and the corresponding stress is treated as the ideal strength. According to the quasi-harmonic Debye model, Debye temperature, the heat capacity, thermal expansion coefficient, internal energy and entropy under temperature of 0～1500 K and pressure of 0-30 GPa are deeply investigated. Particular attention is paid to discuss the rationality of ZrB used as the reinforcement for light metal matrix composites.(4) The structural, phase stabilities, mechanical, electronic and thermodynamic properties of intermetallic phases in Zr-Sn system are investigated by using first-principles method. The configuration of Zr4Sn is measured with reasonable precision. The mechanical properties, including bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio, are calculated by Voigt-Reuss-Hill approximation and the Zr5Sn4 and Zr5Sn3 show excellent mechanical properties. Through the quasi-harmonic Debye model, the Debye temperature, heat capacity and thermal expansion coefficient under temperature of 0～300 K and pressure of 0-50 GPa for Zr5Sn3 and Zr5Sn4 are deeply investigated.(5) The phase compositons and microstructures of Zr-18Nb-xSi (x=1.5,2.0,2.5 and 3.0) are investigated by a combination of XRD and SEM, which are infected by the contents of alloying element Si. The Young’s modulus, compressive strength, plastcic strain and yield strength of the compounds are obtained by using universal testing machine. The results show that the Young’s modulus, compressive strength and yield strength increase with the increasement of Si, however, the plastcic strain decreases with the increasement of Si.